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The Vitamins as Factors in Food Values
Hopkins of Cambridge University was the first to make clear that normal nutrition requires something more than proteins, fats, carbohydrates, and compounds of the mineral elements. He showed that even 90
small amounts of milk (fresh or dried, or of the alcohol-soluble organic material of milk 1) exert a very marked influence upon the growth of young animals kept on a diet of artificially purified food materials, however carefully the purified food substances were chosen to include the right kinds and amounts of proteins and of all the mineral elements required for growth.
Some of Hopkins's results are shown in the accompanying cuts. Figure 4 shows the growth curves of rats with and without
Lower curve six Upper curve six
FIG. 4. - Growth curves of rats.
a small amount of milk when the rest of the diet was of artificially purified food. Figure 5 shows the results of a similar experiment in which on the eighteenth day the milk was transferred
1 The good results obtained by Hopkins with an alcohol-extract of dry milk are attributable to the fact that alcohol dissolves both the fat-soluble and the water-soluble vitamins.
from one set of rats to the other. Note in both cases the failure of growth on the diet of artificially purified foodstuffs alone and the rapid growth when milk was fed.
The previously unknown organic substances essential to normal nutrition whose existence was thus demonstrated by
FIG. 5. - Growth curves of rats. Lower curve (up to 18th day) represents rats on purified food; upper curve similar rats having 3 cc. milk each per day in addition to this food. On the 18th day, marked by the vertical dotted line, the milk was transferred from one set to the other. Abscissæ time in days; ordinates average weight in grams. (Courtesy of Dr. F. Gowland Hopkins.)
While much that we
Hopkins are now known as the vitamins. should like to know about the vitamins is still obscure, and much that has been written about them is confusing, it can be said that all students of the subject now recognize the existence of at least three kinds of vitamins and understand in essentially
the same way the terms vitamin A, vitamin B, and vitamin C. Probably not all the effects which are attributed to vitamins are due to only three chemical substances. There are already reasons for believing that the effects which have been attributed to "vitamin A" are to be separated and assigned to two or three different substances. A similar subdivision of "vitamin B" appears also to be in progress, and we need be neither surprised nor disconcerted if the scientific study of the vitamins should result in further subdivisions. Most, if not all, of our present needs may be served, however, in terms of the threefold classification into vitamins A, B, and C. It will be convenient to consider the water-soluble vitamins B and C before the fat-soluble vitamin A.
Vitamin B is defined both as the water-soluble growth-promoting substance which McCollum called "water-soluble B " and as the antineuritic substance (so-called because it prevents the neuritis or nerve disease of beriberi), to designate which Funk coined the term "vitamine." To most writers, it has seemed probable that the same substance which prevents the neuritis, functions also in the promotion of growth, and has other functions in normal nutrition as well. The term "vitamin B" stands for the food factor which meets these nutritional needs, whether it be a single chemical substance or a group of sub
It appears to be important to appetite and digestion and to bear some relation to general nutrition as well, for it seems that in order to maintain the best condition of nutrition it is necessary to supply the body with more vitamin B than is needed to prevent beriberi, and probably more than is needed to sustain normal growth. Once the matter is understood, however, it is relatively easy to provide an abundance of vitamin B in the dietary because of its wide natural distribution among food products. Milk, eggs, and nearly all parts of plants in their natural state contain vitamin B in liberal amount. Vitamin B also as the most stable of the three vitamins is the least likely
to be destroyed by heat or by oxidation; but being readily soluble in water, much of it may be lost if one rejects the watery portions of canned vegetables or the waters in which vegetables have been cooked.
Vitamin C is called the "antiscorbutic" vitamin because it prevents scurvy, just as vitamin B prevents the neuritis of beriberi.
There is strong evidence that vitamin C not only prevents scurvy but plays an important part in normal nutrition as well, and that our food must furnish us much more vitamin C than is needed for protection from scurvy, if we are to enjoy a full measure of good health and vigor. Hess has pointed out the frequency among young children of cases in which irritability, lack of stamina, and retardation of growth can be cured by the simple addition of more antiscorbutic food to the diet, showing that the diet had been too poor in vitamin C even though no distinct symptoms of scurvy had appeared. Undoubtedly many adult dietaries also are capable of improvement by being made richer in vitamin C; for vitamin C is less widely distributed in food materials than is vitamin B, and being a less stable substance it is more likely to be destroyed in the preservation or the cooking of the food. We shall find, however, that some foods are rich sources of vitamin C and retain this property well, even when heated or stored. This is true of oranges and lemons and their properly preserved juices, and also of ordinary canned tomatoes. Cabbage and onion eaten raw are also rich sources of vitamin C. Apples, bananas, potatoes, and milk contain it in less concentration, but are important sources because of the quantities in which they may be eaten. In some of the subsequent chapters we shall have occasion to consider more fully the occurrence and properties of vitamin C because of its importance as a factor in the nutritive values of certain foods.
Vitamin A may not bear the direct controlling relation to any specific disease that vitamin B does to beriberi or vitamin C to
scurvy; but, of the three, vitamin A is probably the most important to health in America because so many of our staple foods are poor in vitamin A and because a diet poor in this vitamin seems so plainly to lower the general stamina of the body and so greatly to increase its susceptibility to several different infectious diseases. Vitamin A is therefore to be regarded as an important factor in food values.
That certain foods contain a fat-soluble substance of fundamental importance to nutrition was discovered in 1913, independently by McCollum and Davis at the University of Wisconsin and Osborne and Mendel at New Haven, through feeding experiments in which it was found that, with all other conditions the same, young animals would grow normally or fail to grow, depending upon whether the fat in their food mixture was butterfat or lard.
When growth ceases for lack of vitamin A, there also results a greatly increased susceptibility to infection. This seems to be due to a weakening of the membranes in many parts of the body, with the result that the eyes, the air passages and lungs, the skin and the bladder, and even the ear passages and frontal sinus often become affected. Hence it appears that diet poor in vitamin A leads to increased prevalence of disease due to various infections. When the diet furnishes barely enough vitamin A to permit growth and the maintenance of apparently normal health, more is really needed for full vigor, but the nature of this need is apt to go unrecognized. In experiments with laboratory animals the greater vigor conferred by a richer supply of vitamin A becomes very strikingly manifest when animals alike except for the amount of this vitamin in their diet are tested for health and vigor by subjecting them to the added nutritional demands of reproduction and the suckling of young. An individual may appear to thrive on a diet relatively poor in vitamin A, but the results are always deleterious to the offspring (if any are produced) and almost always the individuals