2. Relation of Certain Food Essentials to Structure and Functions of the Body
In my first lecture I confined myself to the more general aspects of the relation of food to nutrition and of both to health and disease. To-day I propose to deal in more detail with those essentials that are needed for the efficient construction and maintenance of the fabric of the body and for the regulation of its processes. It is necessary to be aware of the different parts these substances have to play in nutrition and of the effects of their inadequate supply or inadequate utilization when supplied in sufficient quantities. For then only can it be understood how such inadequacy leads to that disturbance of structure or function of organs or parts of the body which is 'disease'.
These essentials are proteins, mineral elements and vitamins. But before dealing with them something must be said of oxygen and water.
Oxygen and Water
Strictly speaking both oxygen and water are to be regarded as foods, for of all the supplies on which the cells of the body are dependent they are the chief.
The continued and unhampered supply of oxygen -- avallable in the air we breathe -- is, as you know, essential to the continued activities of the body. Respiration depends upon it; tissue-respiration as well as respiration in its commonly understood sense. So also does combustion, both of organic materials ingested as food and of certain substances that result from cellular activity. By its means the latent chemical energy of food is converted into other forms of energy for the work -- both internal and external -- of the body, and the waste products of that work are burned up and disposed of. Thus, the non-volatile substance -- lactic acid -- produced during muscular work, is burned to the volatile carbonic acid which is carried away by the blood and exhaled through the lungs. Without the adequate supply of oxygen the body would become clogged by the accumulation of waste. It is not possible here to discuss the manifold activities of oxygen in the body nor, indeed, is it necessary to do so. It suffices to emphasize the great importance of the efficient oxygenation of the tissues in maintaining the efficiency of the function of nutrition. The proper ventilation of the lungs and the proper exercise of the body are obvious means to this end. These means are complemental to the use of properly constituted food on which, also, the adequate supply of oxygen to the tissues depends.
Water is of outstanding importance to the body, both from the point of view of structure and of function. It is the most abundant constituent of living cells. Its presence therein permits of changes in their form and of their return to their original form after alteration by movements; rapid displacements of substance and the mobility of living matter are thus rendered possible. Its conservation of the boundaries of cells and their restoration after displacements due to motion conserve in their turn the minute internal structure of cells.
Although about two-thirds of the fabric of the body are made up of water, it is not present in all tissues in the same amount. Fatty tissue and bone contain less, the grey matter of the brain, glandular organs and muscle contain more, and the body fluids (blood, etc.) most. The percentage of water is highest in those tissues wherein chemical changes are most rapid, and in tissues that are called upon to function most frequently. The great importance of an adequate supply of water for infants and growing children, in whom metabolic processes are most active, is thus made evident.
Water is the solvent of most of the constituents of protoplasm; it is the vehicle that transports nutrients to the cells, the medium wherein all chemical changes take place within them and the solvent wherein the end-products of these chemical changes are discharged from the body. The evaporation of water from the lungs and skin is one of the chief factors in the regulation of body temperature. It has, too, various mechanical functions such as in facilitating the movements of mobile parts (for example, joint surfaces and coils of intestine) one upon another. The functional efficiency of the digestive tract, the normal production of the digestive juices, the normal absorption of food and the normal action of the bowels may be cited as conspicuous examples of the need of the body for an adequate supply of water.
Water is constantly being discharged from the body by way of the skin (perspiration), lungs (exhalation), kidneys (urination) and bowel (defaecation). This loss is partly replaced by the water contained in solid food and by that produced in the chemical reactions of metabolism. But over and above this more than a quart, as such or in beverages, is needed daily to make good the loss. The need of the cells and tissues for water is expressed in that indefinite sensation which we call 'thirst'. The first rule in dietetics is to drink water in abundance.
The insufficient ingestion of water gives rise to headache, loss of appetite, disturbance of digestive functions and of the action of the bowels, nervousness and impaired capacity for work, mental or physical. In infants the loss of water consequent on diarrhoea, vomiting or excessive evaporation from the lungs may cause serious symptoms: failure of digestive processes consequent on diminished production of the digestive juices, rapid loss of weight, dry skin, exhaustion, coma and convulsions.
Proteins are the next most abundant constituents of living cells. Their chief role in the body is to provide materials for its growth and for the repair of its tissues. There is a constant utilization of proteins in these ways, a continual voiding of the waste products of their metabolism. Their continuous supply is, therefore, necessary; and this supply must be of the right kind, to furnish the requisite amino-acids from which the tissues of various parts of the body are built up. Besides their function as providers of building-materials they also furnish a certain amount of energy. They are the source from which the body elaborates certain enzymes, or ferments, such as those concerned in the digestive processes, and catalytic agents -- glutothione, thyroxine, adrenaline and insulin -- needed for the speeding up of chemical processes.
The daily requirements of the body for proteins are approximately 1.0 gramme per kilogramme of normal bodyweight; more than this is an undesirable excess. Sources of them amongst animal foods are milk, meat, glandular organs, eggs and fish; and amongst vegetable foods, legumes, whole cereal grains, seeds, nuts and green vegetables. Those derived from animal sources are, in general, more suited to the needs of the human body than those derived from vegetable sources. The former are, in consequence, sometimes spoken of as 'good', 'suitable' or 'first-class' protein, and the latter as 'second-class' protein. But it is not necessary that the protein requirements of the body should be derived chiefly from animal sources; it suffices if one-third of them be so derived. Nor is it necessary that 'good' protein be derived from 'meat'. Those of milk are amongst the best of all proteins and well able 'to leaven the whole lump' of those derived from vegetable foods. For this reason, amongst others, presently to be referred to, the use of milk and cheese as articles of diet, should be greatly extended. Much greater use should also be made of the better class vegetable proteins, such as those of soya bean, legumes and nuts, and much less use of the flesh of animals. Apart from every other consideration the use of meat as the main source of proteins is as uneconomical as it is unnecessary; but where flavour is there will desire be also.
It will be obvious from these considerations that the insufficient ingestion, absorption or assimilation of proteins, or of proteins of the right kind, will tend to degradation of vital processes; a degradation manifested in stunting of growth, poor physique, lack of energy, resource and initiative, digestive disturbances and impaired action of glandular organs. To these there may be added a lowered resistance to infection. Severe degrees of protein-starvation, associated as they often are with want of food in general, may give rise to a condition known as 'malnutritional oedema', 'war oedema' or 'famine oedema' in which the body, in part or in whole, becomes waterlogged.
The mineral constituents of food consist of some twenty elements of which eleven -- previously enumerated (Chapter 1) -- are definitely known to be essential to vital processes. They are all intimately related one to another by complex chemical combinations and interactions, so that it is difficult to separate the functions of one from those of another. In general these functions are to provide building materials for the fabric, and to regulate various functions, of the body. In fulfilment of the first function some enter into the composition of all cells while others form the major part of the skeleton and teeth. In fulfilment of their regulating functions they have various parts to play: all are concerned in controlling the normal exchanges of body-fluids and the permeability of the cell membranes; some maintain and regulate the neutrality of the blood, others the normal contractility of muscles and excitability of nerves; some enter into the composition of the digestive juices; others take part in the transport of oxygen from the lungs to the tissues and of carbon dioxide from the tissues to the lungs, thus making oxidation processes possible. Indeed, it may be said that the more the mineral constituents of food are studied, the more important is their role in nutrition found to be. It is essential to remember this importance in view of the prominence which nowadays is given to vitamins -- the one class of substances is as important as the other.
Mineral substances are continually being lost by the body by way of the excretions, and their replacement is constantly necessary. Thus, in certain circumstances, the loss of salt may be excessive and give rise, if not replaced, to distressing symptoms. Herbivorous animals, and those human beings whose food is vegetarian, require more salt than carnivora or flesh-eaters.
From the point of view of dietary construction, four of these mineral elements -- calcium, phosphorus, iron and iodine -- are of outstanding importance; not only because of their own functions but because they are those most likely to be present in the average diet in insufficient quantities. In constructing diets the amounts of these minerals should be adjusted with the same care as is given to those of proteins, carbohydrates, fats and vitamins; and, in estimating the quantities of essential components in any diet, the calculations should always include these four elements. By making provision for their ample supply no serious deficiency of any other mineral essential is likely to arise.
Calcium. -- Calcium is one of the most important, as well as most widespread, of all constituents of the body. It is a chief constituent of the bones and of the teeth. It controls the contractility of muscle including that of involuntary muscles such as those of the gastro-intestinal tract. The rhythmic beat of the heart depends to a great extent upon it, as do the movements of cilia (vide infra). It maintains the normal response of the nerves to stimuli, preventing their hyper-irritability, preserves the clotting power of the blood, and sustains the capillary circulation. It co-ordinates the activities of certain other mineral elements.
Calcium is made use of in the body to the extent of about 0.68 gramme daily; but to allow a fair margin for waste and non-absorption the food should provide at least a gramme a day. The allowance for expectant mothers and for growing children should be even greater. The growth of the bones and teeth as well as of the body generally, menstruation, pregnancy and lactation make special demands for its abundant supply, more especially in western countries where sunshine is scanty and the intake of vitamin D -- a substance controlling the absorption and utilization of calcium -- is low.
The insufficient supply of calcium in the food is one of the commonest of all food-faults in this country. Indeed, it is difficult for the growing child, under modern conditions of life and food-supply, to obtain enough calcium unless the diet contains at least a pint of milk a day -- milk being a rich source of it. This is another cogent reason for the greater use of milk as an article of diet. The diet of pregnant women is often dangerously low in calcium. Recent researches in America have shown that such women need 1.6 grammes daily: often they do not receive more than one-half of this amount. Its deficiency leads to the imperfect building of bones and teeth, in growing children to rickets and all its attendant consequences, to malformation or mal-alignment of the vertebrae and spinal curvature, and to decay of teeth. To satisfy the urgent demands for this important element elsewhere it may be withdrawn from the bones -- its storehouse in the body. Not infrequently the normal calcium content of the blood, on which so many bodily activities rely, is being maintained at the expense of decalcification elsewhere -- of teeth, alveoli and bones. The clinical expressions of such decalcification are softening of bone, weakness of bone, increased liability to fractures, retraction of the alveoli in which the teeth are set, and dental decay. Want of calcium leads also to nervous excitability and to a condition known as tetany, to impaired muscular activity, both of voluntary and of involuntary muscles, and to disturbance of cardiac rhythm and of the neutrality of the blood; it may also be a cause of chilblains and of irritability of the skin. Foods rich in calcium are milk, cheese, turnip-top greens, black treacle, almonds, watercress, egg-yolk, peas, beans and green leafy vegetables of various kinds.
Phosphorus. -- Phosphorus is an essential component of the nuclei of all cells. It therefore plays a conspicuous part in all cellular activities. It enters largely into the composition of the bones and teeth, and is needed for the manufacture of the lipins which abound in all tissues, and more especially in the nervous tissues. It should be provided in the diet to the extent of about 1.5 grammes daily -- alike for women and children as for men -- and for the same reasons as for the abundant supply of calcium. During pregnancy the amount should be increased, according to recent findings, to as much as two grammes daily.
Deficiency of phosphorus may lead to stunting of growth, poor bone formation, softening of bone, a certain type of rickets, tooth decay, disturbance of the normal neutrality of the blood and to depression of vital processes generally. Foods rich in phosphorus are cheese, egg-yolk, lean meat, almonds, nuts, whole wheat, liver, milk, fresh beans, spinach, brussels sprouts and potatoes.
Iron. -- Iron is an essential constituent of the nuclei of all cells, and as such it is concerned in the control of all cellular activities. It is an essential constituent of the red pigment -- haemoglobin -- of the blood. Haemoglobin is the carrier of oxygen from the lungs to the tissue-cells; it is obvious, therefore, that iron in this, if in no other, capacity plays a vital part in the economy of the body. The daily loss of iron is from seven to eight milligrammes by way of the faeces and about one milligramme by way of the kidneys. In all there are lost about ten milligrammes daily, or about one-three hundredth part of the total haemoglobin-iron in the body. It has been estimated that the iron content of the average diet in this country is rarely more than ten milligrammes, while it is frequently as low as five. In these circumstances, ill health is likely to arise. This takes the form of anaemia, which, as is now known, is a common ailment, especially in infants and in women of the childbearing period of life; in the former, because of the paucity of iron in the mother's or in cow's milk; in the latter, because of its insufficient ingestion or assimilation.
The diet should contain at least fifteen milligrammes of iron daily. During pregnancy this amount ought to be increased to twenty milligrammes. Foods rich in iron are lentils, egg-yolk, liver, beans, black treacle, oatmeal, whole wheat, turnip tops, spinach, prunes, dates and raisins. It is to be noted that milk is poor in iron. Nature compensates to some extent for this defect in milk by bringing the child into the world with a fair store of iron in its own tissues; but this store does not always protect the infant from anaemia when the mother's milk is poor in iron or when the child is fed on cow's milk.
Iodine. -- Iodine is an essential constituent of the thyroid gland -- its chief storehouse in the body -- and of the active principle of the gland, thyroxine. It is necessary for the normal functional activity of this important organ whose action is to the oxidation processes of the body not unlike that of the bellows to the fire -- thyroxine speeds up the rate of these processes. In normal circumstances, the daily requirements of iodine are about fifty gamma (1-1000th of a milligramme). Growing children, pregnant and lactating women, need more of it than others. More also is needed when the diet is rich in fats or contains an excess of lime, and more in some conditions of insanitation, of infection as of the intestinal tract and, indeed, of infections generally. Its deficiency in the diet admits of the operation of certain agents causing goitre: a malady likely to give rise to cretinism, deaf-mutism and idiocy in the offspring of goitrous women. In regions where goitre is endemic, the iodine-content of water-supplies and locally produced foodstuffs is low. Rich sources of iodine are sea-foods and cod-liver oil.
Other important mineral elements are magnesium, copper, chlorine. fluorine and sulphur. The first has important physiological functions, particularly in relation to the movements of body-fluids. The second is invariably present in the brain and has a relation to the blood, being complemental to iron in the prevention of anaemia. The third (chlorine) plays a leading part in the alkali chlorides of the blood and tissues and in the hydrochloric acid of the gastric juice. The fourth (fluorine) is a normal constituent of bones and teeth; it is not devoid of significance in the formation of these tissues. The fifth (sulphur) in the form of the complex amino-acid, cystine, is essential for growth, is a constituent of certain catalytic agents, and has a relation to the nutrition of joints.
It is commonly believed that if the foodstuffs of which a diet is composed be varied enough, there is little likelihood of deficiency of any important mineral elements. This is no doubt true; but the variety is often not sufficiently great nor of a kind to ensure an adequate supply of them. In this connection I quote the following from the British Medical Journal of 29th December 1934: 'The average diet in this country contains from 5 to 10 mg. of iron.' It is apparent, therefore, that the average diet is not varied enough to provide a sufficiency of this most important element, nor is it always varied enough to provide a sufficient amount of lime. The truth is that the common belief -- safety in variety -- is likely to be misleading; for, as McCollum showed years ago, one can ring the changes on a great variety of foodstuffs -- muscle meats, cereal grains, tubers, roots, potatoes, peas and beans -- and yet have failure of nutrition unless the diet contains a sufficiency of the protective foods -- milk and green leafy vegetables. This applies to vitamins as well as to mineral elements.
The vitamins, according to present knowledge, are of five classes, designated by the letters of the alphabet: A, B, C, D, and E. Each has its own part to play in nutrition -- a part that cannot be taken by any other.
Vitamin A. -- Vitamin A is essential to growth and development of the young and 'to the orderly progression of nutritional processes at all ages' (Sherman). It is essential to the young in the way that without a sufficient supply of it pathological states are likely to arise and to interfere with growth and development. It is a promoter of vigour and stamina, and plays a part in maintaining the structure and function of the nervous system. It is one of the most important of the food essentials concerned in the efficiency of the function of reproduction and the rearing of the young; hence the importance of its adequate supply to pregnant and nursing women. It is a potent factor in maintaining the resistance of the body to infection. This it effects by its specific relation to epithelia throughout the body: that of the skin, of the mucous membranes (particularly of the respiratory and the alimentary tracts), of the glands of external secretion and their ducts, of the thyroid, the interior of the eye, the lungs, the kidneys, the bladder and all passages leading to the exterior of the body. Its deficiency gives rise to structural changes in epithelium which impair its functions and lower the local defences against infection. In this sense, and in this sense only, it is anti-infective. Diminished resistance to local infection may be the first evidence of its deficiency, and the pathological state resulting therefrom the first clinical evidence that nutrition is at fault. Much more of it is needed for the prevention of infection than for growth. Let me draw your attention to the kind of change that is brought about in epithelium by lack of this vitamin. (Pictures showing in cross-section the mucous membrane of the upper respiratory passages of rats were here exhibited.) (Fig. 4) This membrane is covered by tall epithelial cells, each of which has a fringe of cilia. A function of these cells is to secrete mucus which not only traps bacteria but permits the cilia to perform their movements -- this they can only do when the membrane they fringe is moist and the moisture contains calcium. The function of the cilia is, by their rapid movements in waves, to propel bacteria or foreign particles, as of dust, towards the exterior of the body, whence, in normal circumstances, they are ejected. It has been estimated that the cilia move at the rate of about 600 times a minute. Now when the food is deficient in vitamin A the cilia slough off and the cells themselves lose their secretory character, becoming horny or keratinized, as it is called. Figure to yourselves what this means: no longer is this trapping, this propelling of harmful particles, whether of dust or bacteria or both, possible in the areas so affected. For, unless the deficiency be very grave, it is only at certain places that these changes occur. Where they do occur the local defences are broken down and bacteria are free to implant themselves in the soil thus made ready for them and to invade the tissues. And it is a curious fact that, in these circumstances, bacteria that may otherwise exist as harmless saprophytes often take on pathogenic properties and become disease-producing. Mark how serious a view the body takes of these events: at once it sends up defence forces in the form of round cells to man the breach, and these may accumulate to such an extent as actually to form adenoid-like outgrowths.
Section of mucous membrane through upper part of trachea of well-fed rat receiving adequate supplies of vitamin A in the diet. Note normal appearance of the columnar epithelium, the fringe of cilia and the normal number of round cells beneath the epithelium.
Section of mucous membrane through upper part of trachea of rat whose diet was deficient in vitamin A. Note disappearance of cilia, keratinization of epithelium, flaking of same and increasing numbers of round cells beneath the epithelium. Similar changes occur in epithelial structures generally (conjunctiva, bladder, vagina, etc.)
Section of mucous membrane through upper part of trachea of rat whose diet was deficient in vitamin A, showing a later stage of the process seen in previous figure. The keratinization process is more advanced and round cells have accumulated beneath the keratinized epithelium in greater numbers.
Section of mucous membrane through upper part of trachea of rat whose diet was deficient in vitamin A. Note normal appearance of mucous membrane except limited area where the process shown in previous figures has occurred. A notable feature of this process is its frequently patchy character.
The maladies resulting from deficiency of vitamin A are, with the exception of night-blindness, usually the result of superimposed infection. They involve, singly or in combination, many systems of the body: ocular, nervous, cutaneous, buccal, dental, gastro-intestinal, urinary and reproductive. Such diverse conditions as xerophthalmia, pneumonia, colitis, stomatitis, gastric ulcer, one form of goitre and stone-in-the-bladder may arise in consequence of its inadequate supply in the food of rats. Some of these conditions, such as xerophthalmia, night-blindness, stomatitis, catarrhs of all sorts, and certain skin affections are definitely known to occur also in man from this cause; and, for my own part, I do not doubt but that the future will reveal a number of others that are due also to this cause in man: disease of the respiratory and gastro-intestinal tracts in particular. It is to be emphasized that many of the local maladies brought about by deficiency of this vitamin are often, because of the local infection associated with it, not readily curable by the provision of the vitamin; the reason no doubt being that pathogenic organisms, once they have taken root, are difficult to eradicate, especially in parts of the body where structural and functional changes have taken place. The fact that the administration of the vitamin by the mouth may not cure a certain condition is, therefore, no sufficient reason for the supposition that its deficiency may not have been a cause of it. Sub-optimum supply of vitamin A may be associated with no clinical signs of disease, depending on the degree of the deficiency, the age of the subject and the absence of infection. It may, indeed, be only by the sense of well-being, resulting from its more abundant provision, that its sub-optimum supply becomes apparent. As Sherman says of it: 'Its bountiful supply is a bulwark against disease of many kinds, a promoter of vigour, stamina, and that condition of body and its various parts and functions which conduces to efficient and prolonged life.'
Rich sources of Vitamin A or of its precursor (carotene) are animal fats, cod liver oil, milk, butter, liver, eggs, herrings, carrots and fresh, green vegetables.
Vitamin B. -- Vitamin B is a complex, said to consist of some five or six fractions, each having its own particular function. Their separation is largely a laboratory manoeuvre -- a feat rarely indulged in by Nature, though some foodstuffs contain more of one fraction of the complex than of others. It is enough for the layman to know what are the chief functions of two of its principal parts: vitamin B1 and vitamin B2 (the latter itself a complex). Both are essential for growth (Fig. 5); one (B1) is destroyed by heat; the other (B2) is not.
Figure 5. Effect on the growth and mortality of young rats of adding vitamins to a basal diet devoid of them but otherwise complete.
Vitamin B1 is intimately concerned with the maintenance of neuromuscular efficiency throughout the body, such, for instance, as that of the stomach, the colon and the heart. Within an hour of the administration of a dose of the International Standard Preparation of the vitamin to a person whose diet is low in this factor, but who may show no obvious sign of its lowness, the heart's action is markedly improved and remains so for approximately four hours, when the good effect wears off. If, however, the same dose be given to a person whose diet contains enough of it, no effect on the heart is observable on electro-cardiographic examination. In animals (pigeons and rats), under experimental conditions, its deficiency gives rise to marked slowing of the heart's action (bradycardia) amounting sometimes to 'heart-block'. It causes also a slowing down of respiration and a fall in body temperature and in blood pressure. Its deficiency has a specific effect on the adrenal glands (causing them to undergo hypertrophy) and through them, as well as more directly, on the sympathetic nervous system. Appetite is dependent in great measure, on an adequate supply of it -- appetite for water as well as for food. It has an important influence on the secretory activity of the stomach, its deficiency greatly impairing the production of gastric juices. In its absence or inadequate supply the muscular movements of the stomach and of the lower bowel are much impaired. This impairment of the secretory and motor functions of the stomach deranges the function of nutrition at its very outset. It also influences nutrition in a number of other ways. Thus it promotes the assimilation of food and the multiplication of cells (growth). An interesting example of the latter is afforded by the developing chick's intestine when grown in vitro. Explanted, about the eighteenth day of development, in normal fowl plasma, it grows profusely; but when explanted in plasma from a fowl fed on polished rice -- which is deficient in this vitamin -- growth is scanty or altogether inhibited. Further, if the vigorously growing tissue be transferred from the normal to the deficient plasma, growth immediately ceases and the young cells undergo rapid disintegration. It is notable that intestinal tissue is particularly sensitive in this respect -- a fact which can scarcely be without significance in relation to the immature gastro-intestinal tract of infants.
Amongst other effects of want of this vitamin are degeneration of lymphatic tissue, atrophic changes in the spleen and sex glands, disturbance of carbohydrate metabolism, reduction of the glycogen normally stored in the liver and the accumulation of a toxic substance (lactic acid) in certain tissues which may cause functional paralysis and convulsive seizures. Beri-beri is always associated with deficiency of this vitamin, though the vitamin deficiency is not always followed by beri-beri; the deficiency is not the only factor concerned in its causation. Beri-beri is rarely encountered in this country; but it is not unlikely that other forms of neuritis, such, for instance, as alcoholic neuritis, may be due as much to inadequate absorption of vitamin B1 consequent on derangement of digestive processes, as to toxic action.
The insufficient ingestion of vitamin B1 is a common food fault, due mainly to the extensive use of vitamin-poor or vitamin-less carbohydrate foods, such as polished rice, white flour and sugar. It has to be remembered in this connection that the more carbohydrate eaten the more vitamin B1 is required. The effects of its inadequate provision are loss of appetite, impaired digestion, decreased motility of the stomach, sluggish bowel action, impaired growth of the young during the lactating period consequent on deficiency in the mother's milk, deranged function of the adrenal glands (possibly a cause of distressing dreams), nervousness, loss of weight and vigour, and fatigue. In infants there may be stiffness of the arms and legs, rigidity of the neck, restlessness, fretfulness and pallor. This vitamin has an important relation to the secretion of milk, much more of it being needed during the lactation period than at other times. Its abundant provision during pregnancy is also of great importance. Its richest natural source is dried brewer's yeast. Rice polishings, bran and wheat-germ are all good sources of it, as are whole cereal grains. Yolk of egg, liver, kidney, heart, watercress, cabbage, spinach, lettuce, carrots and tomatoes are other excellent sources. It is to be noted that milk and muscle meat are relatively poor in this vitamin, so are fruits. An important practical point is that, when vegetables are cooked in water and the water thrown away, more than half of this water-soluble vitamin is lost.
Vitamin B2 is especially concerned in maintaining the health of the skin -- both that covering the exterior of the body and that -- the mucous membrane of the alimentary tract -- lining its interior. It is concerned also in maintaining the integrity of the nervous system, and appears to have some part to play in the prevention of anaemia. It bears a quantitative relation to the fat-content of the diet: the more fat ingested the more vitamin B2 is needed -- a fact not to be forgotten when the digestion of fats is found to be poor.
Deficiency in the diet of this fraction of vitamin B gives rise to gastro-intestinal disorder (degenerative and inflammatory states, such as gastritis, enteritis and colitis), to lesions of the skin and, when the deprivation is severe, to mental derangement. It, or a fraction of it, is specifically related to the disease known as pellagra; but this relation appears to be much the same as that of iodine-deficiency to goitre or of B1-deficiency to beri-beri -- it is not the sole, nor probably the ultimate, cause. Of far greater importance is it to keep in mind that a generous provision of vitamin B2 is one of the factors on which the health of the skin, the gastro-intestinal tract and the nervous system depends. In rats under experimental conditions, cataract has been observed to result from its want.
It is not yet definitely known whether it is the B1 or the B2 fraction of the complex which contributes so markedly to the prevention of microbic invasion of the body. This is not a matter of great practical importance, so long as it is recognized that vitamin B does play a part in this connection. Many years ago I showed that, in animals fed on food deficient in vitamin B, bacteria were apt to find their way through the walls of the intestine into the blood-stream. Further, bacteria normally absent from the small intestine may migrate thereto from the colon where, normally, they are present; in the latter location they are harmless, even useful, in the former they have a noxious action.
The vitamin B-complex appears, as does vitamin C, to have some relation to the nutrition of the joints. Recent investigations in regard to rheumatism indicate the need for the adequate supply of both these vitamins in this condition.
Rich sources of vitamin B2 are dried brewer's yeast, liver, kidney, muscle meat, eggs, milk and green leafy vegetables. It is to be noted that whole cereal grains are in general poor sources of B2 though relatively rich sources of B1, that muscle meat and milk, while rich in B2 are relatively poor in B1, and that white of egg is the only known food in which vitamin B2 occurs without B1.
Vitamin C -- Vitamin C is now known to be identical with ascorbic acid -- a potent reducing agent. It is thought that the biological activity of ascorbic acid may depend on its double function of oxidation and reduction. If this be so its deficiency in the diet would involve the depression of oxidation processes. Vitamin C has a specific relation to the supporting tissues of the body, 'enabling the cells to produce and to conserve inter-cellular substances that cause setting of the matrix in which the cells lie and are supported' -- an enlightening observation which we owe to two American observers. It is as if the bricks of which a house is built were to produce substances that caused the mortar supporting them to set, and went on doing so to prevent its upsetting. This function has a particular concern for the blood capillaries; the cells comprising which may become loosened in their settings for want of it and blood extrude between them into the tissues.
Deficiency of vitamin C may lead to haemorrhages in various parts of the body, to sallowness and other affections of the skin, to fragility of bones, swelling of joints, imperfections in the teeth, unhealthy gums, congestion of the bladder, changes in the bone-marrow, gastro-intestinal disorder (such as duodenal ulcer -- in guinea-pigs), and to latent or manifest scurvy. Like vitamin B it has a specific relation to the adrenal glands -- its chief storehouse in the body -- which undergo enlargement when it is deficient in the diet. This observation, which I made in 1919, calls to mind the enlargement of the thyroid gland -- the chief storehouse of iodine in the body -- which results from deficiency of iodine. Like proteins and vitamins A and B, but in its own particular way, vitamin C has an anti-infective action. It has, for instance, recently been shown that guinea-pigs, fed on diets poor in vitamin C but not sufficiently lacking in it to cause manifest scurvy, develop the symptoms characteristic of rheumatic fever when streptococci, isolated from cases of this disease in human beings, are administered to them; guinea-pigs receiving diets rich in vitamin C do not, or only in relatively few cases, develop these symptoms when similarly treated. The same appears to be true of intestinal tuberculosis: a high proportion of those receiving too little vitamin C develop tuberculous ulceration of the intestine when virulent tubercle bacilli are administered to them by the mouth, while only a small proportion of those receiving abundance of vitamin C develop this condition when similarly treated. These observations in guinea-pigs may prove to be of significance in regard to rheumatism and intestinal tuberculosis in man; for man resembles the guinea-pig in that he is equally sensitive to want of vitamin C.
Rich sources of vitamin C are parsley, orange peel, green chillies, cabbage, orange juice, lemon juice, brussels sprouts, caulifower and other green leafy vegetables. It is to be remembered that leafy vegetables rapidly lose a great part of their content of this vitamin as their freshness diminishes.
Vitamin D. -- The function of this vitamin is to promote the absorption of calcium from the intestine and to assist in maintaining its normal level in the blood. It is a chief regulator of calcium and phosphorus metabolism and the fixer of calcium in the bones and teeth. Through this regulation it serves to ensure and to maintain the normal structure of the bony framework of the body and of the teeth. It is associated, in the control of calcium metabolism, with the parathyroid glands whose secretion is a mobilizer of calcium, releasing it as occasion demands or as exceptional circumstances determine from the bony structures of the body. The metabolism of calcium is thus controlled by a substance derived from food as well as by a substance manufactured by the body itself. The deposition of lime and phosphorus in growing bones is also related to a ferment -- phosphatase -- which is normally present in them.
This vitamin has an important relation to the bone marrow, helping to ensure the normal proportions of its cellular constituents. Its deficiency in the diet leads to mal-absorption of calcium from the intestine, to shortage of calcium in the blood, to the imperfect deposition of lime and phosphorus in the bones, and to the occurrence of rickets. The structure of teeth is similarly impaired by its want, with resultant dental decay. Enlargement of lymphatic glands in various parts of the body -- neck, groin and axilla -- may also result from its inadequate supply. Another malady to the causation of which deficiency of vitamin D contributes is osteomalacia; a condition in which great deformity of bones occurs. This malady is common in certain parts of India and China and is usually confined to women. A very important consequence of deformities of bone brought about in these ways is alteration in contour of the pelvis; it is one that may give rise to serious difficulties during childbirth. Chilblains may be caused by partial deficiency of this vitamin in association with calcium-insufficiency.
It is not known whether vitamin D has any special anti-infective action, though sufferers from rickets are very prone to certain infections, especially of the respiratory tract. Rickets of severe type is, happily, much less common in this country than formerly, although, as recently as 1928, it was stated that 90 per cent of elementary schoolchildren in London suffered from minor degrees of it.
The animal organism is endowed with the capacity to manufacture its own vitamin D following exposure of the body to the ultra-violet rays of the sun. Foods may also be activated in the same way or by artificial ultra-violet irradiation. Vitamin D is nowadays manufactured synthetically by the ultra-violet irradiation of ergosterol. The product is known as calciferol and is potent in very small dosage.
The sources of this vitamin are relatively scanty: cod liver oil, halibut and other fish oils, liver, kidney, butter and yolk of egg are the chief. It is, indeed, difficult in countries where sunshine is scanty for children to obtain enough of it unless the diet is fortified by the addition to it of cod liver oil or of calciferol. In the administration of the latter great care must be taken to avoid overdosage, the effects of which may be serious. Rickets is by no means unknown in the tropics, usually occurring in those castes observing the Purdah system.
Vitamin E. -- Vitamin E is concerned in the maintenance of the functional efficiency of the reproductive system: a concern which it shares with protein, and with vitamins A and B. It is not yet clear that it has any very important part to play in this regard in human beings. It is widely distributed amongst foodstuffs; occurring in wheat germ, eggs, milk, meat, lettuce, spinach, watercress, coconut oil, cotton seed and a number of others.
Vitamins in General
It will be apparent from the foregoing facts that each vitamin has specific relations to certain structures of the body: vitamin A to epithelium and nerve; vitamin B to the gastro-intestinal tract, nervous system and skin; vitamin C to the cement substance that binds the cells of the body together; vitamin D to the bones and teeth; and vitamin E to the reproductive system. Their relations are not, however, confined to these: thus, one may support another in maintaining the health of the skin, the teeth, the bones, the gastro-intestinal tract, or the nervous system; and all are closely intertwined in their action with other essential constituents of the food. Consider, for example, the factors concerned in maintaining the structure and health of the teeth. There are, to begin with, the minerals -- calcium and phosphorus -- of which the teeth are mainly composed and of which an adequate supply must not only be provided in the food but adequately absorbed from the intestinal tract. There is the vitamin D needed to ensure both the proper absorption of calcium and its proper deposition -- together with phosphorus -- in the teeth. There is the vitamin C required to maintain the matrix in which the cells of the teeth lie. There are the vitamins A, C and B2 needed for the maintenance of the health of the gums and alveoli in which the teeth are set. All of these are essential to the normal structure and health of the teeth, and deficiency of any one of them may give rise to dental decay. The dietetic causes of dental caries are, therefore, multiple (and not the least of these is the excessive use of sugar). The same is true of many other diseases of a degenerative kind in the causation of which malnutrition is concerned. For the maintenance of health of any organ or part of the body the adequate supply of all things needed for normal nutrition is necessary. It is true that the outstanding deficiency of one or other essential may give to the resultant disturbances of structure or function characters which we recognize as specific disease entities, but even then default of other essentials may contribute to their production.
It is during the early and growing period of life that an optimum supply of all vitamins, as well as of other essentials concerned in the maintenance of structure and function of the body, is so necessary. For the foundations of disease are often laid by their inadequate provision in early life. This is particularly true of deficiency of vitamins A and B, which may leave behind them diseased states -- as of the gastro-intestinal tract -- that subsequent administration of these vitamins by the mouth may be unable to remedy, though their parenteral administration may prove more effective. During pregnancy also -- and lactation -- an abundant supply of vitamins of every kind is needful, as well for the child as for the mother. Indeed, at all times optimum efficiency of the body and of its various functions depends, in great part, on an optimum supply of vitamins. Their function is not merely the prevention of the 'deficiency diseases' -- xerophthalmia, beri-beri, pellagra, scurvy and rickets -- with which they are usually associated by name; being called 'anti-this' or 'anti-that'. The use of these limiting descriptive terms -- 'anti-xerophthalmia', 'anti-beri-beri', 'anti-scorbutic' and so on -- however well they may have served their purpose in the past, when we were largely groping in the dark, is, as I pointed out fifteen years ago, objectionable. For they concentrate attention on particular 'deficiency diseases' and convey the impression that all the vitamins have to do is to prevent them. Attention is thus diverted from their far more important relations to structure and functions of the body as a whole. All these specific deficiency diseases are associated in their origin with severe degrees of vitamin-deprivation. But outside the laboratory these severe degrees are encountered relatively rarely. Milder degrees are much more common; and, as far as vitamins A, B and C are concerned, bacterial or other pathogenic agents may, and often do, combine with these milder degrees of vitamin-deficiency to produce illnesses differing widely from the specific deficiency diseases with which the vitamins are commonly associated in the professional and lay mind. The inadequate ingestion of vitamin A does not, for instance, always cause xerophthalmia; infections of the lungs, skin or intestinal tract are often the consequences of it. So, too, with vitamin B: poor appetite, some digestive disturbance, nervousness, feeble action of the heart, lack of vigour and fatigue may be evidences of its inadequate supply, where no signs of beri-beri exist. Similarly, in regard to insufficiency of vitamin C, there may be no manifest signs of scurvy yet it may be present in a latent form, as that great authority on the subject -- the late Alfred Hess -- assured us that it often is. No teaching could be more purblind, in the light of our present knowledge (incomplete though it be) of the important relations of the vitamins to structure and functions of the body, than that which affirms there is no insufficiency of vitamins A, B, C or D because there is no xerophthalmia, no beri-beri, no pellagra, no scurvy or no rickets. There may be no vitamin-insufficiency; on the other hand, there often is. I speak now of optimum health; not of that sub-optimal state of being which so many are content to regard as good health.
Since the year 1921 I have used every occasion to emphasize that it is the lesser degrees of vitamin-deficiency, and the less obvious manifestations of such deficiency that are of importance in Western countries. A recognition of this fact is, I believe, essential to the prevention and cure of many of the commoner sicknesses of mankind -- sicknesses to which we cannot always attach a diagnostic label. 'It is rare', as I wrote in 1921, 'that the food of human beings is totally devoid of any one vitamin; it is more usual for the deficiency to be partial, and for more than one vitamin to be partially deficient; it is more usual still for partial deficiency of vitamins to be associated with deficiency of suitable protein and inorganic salts and with an excessive richness of the food in carbohydrates. Consequently, the manifestations of disease resulting from the faulty food are compounded of the several degrees of avitaminosis on the one hand, and of ill-balance of the food on the other. Nor is this all, for pathogenic organisms present in the body, during the period of its subjection to the faulty food, contribute their share to the general morbid results. ... Other factors also, such as age, sex, individual idiosyncrasy, rate of metabolism, fatigue, cold, insanitary surroundings, overcrowding, the varying susceptibilities of different individuals, of different organs and of the same organs in different individuals, all play a determining part in the production of the morbid result of food deficiency. So it is that in practice the manifestations of deficiency disease are influenced by a number of factors apart from the actual food fault. It may be expected, therefore, that wide variations in the incidence, the time of onset, and the character of the symptoms will occur in human beings in whom the dietetic fault has been to all appearances the same. ... It is to this variety of morbid change that I desire to draw attention ... since it seems to me to impart to the term "deficiency disease" a wider significance than has been attached to it hitherto.' At the time these words were written they were received with some scepticism, yet to-day 'it is becoming generally recognized that much subnormal health and development, and even incidence of disease, are associated with a partial deficiency of one or more of the accessory substances'. (Medical Research Council's Report on Vitamins, 1932.)
If the knowledge acquired during the past quarter of a century is to yield its fullest fruit in the betterment of the national health it must be recognized that an optimum supply of all vitamins, in an otherwise well-balanced diet, is a prerequisite of optimum health; and that a minimum supply, while it may suffice for the prevention of certain specific 'deficiency diseases', creates the conditions precedent to the occurrence of a wide range of other sicknesses.
All of which, in regard to vitamins, is not to minimize the great importance of other food-essentials in maintaining nutritional harmony and this, in its turn, the melody of health.