In the small intestine, both vitamin A and carotene must combine with bile salts before they can pass into the blood. If the diet is low in fat, little or no bile reaches the intestine, and 90 per cent of both carotene and vitamin A may be lost in the feces. Not all the carotene which reaches the blood is changed into vitamin A. Unless the vitamin-E intake is adequate, any vitamin A reaching the blood is destroyed, and any already stored is quickly used up. Vitamin A cannot be stored if the B vitamin, cholin, is undersupplied. When one considers all of these points, one wonders how people have obtained enough vitamin A to stay alive. If you plan carefully, however, you can probably buy 50 times more vitamin A with the same amount of money this week than you did last; some of it will certainly be absorbed, and there may even be an excess for storage. Select your fruits and vegetables for their yellow or green color. Serve liver, kidneys, cheese dishes, or an egg souffle more often than roasts, chops, and steaks. Use storage butter and eggs rather than winter products. Grow carotene-rich vegetables in your garden and freeze them for winter. Since carotene and vitamin A dissolve in fat, and since fat can be stored in the body, this vitamin is stored, provided an excess is absorbed and not destroyed. The vitamin is stored largely in the liver; the amount can be doubled if the intake of vitamin E is adequate. This stored vitamin A can be called upon to meet your needs whenever your diet is inadequate. Experimental animals, given an excess of the vitamin A, store a hundred times more than is necessary to produce all appearances of good health. Analysis of human livers indicates that the same is true of people. Animal experiments show that a generous storage of vitamin A is advantageous during both health and disease. Toxicity to massive doses of this vitamin has been reported when halibut-liver oil has been taken by tablespoon rather than by drops. The toxic amount appears to be approximately 10,000 times the daily need. Physicians have frequently recommended curative doses of 200,000 units daily for months, and children have been given 300,000 units daily 5 over long periods without apparent harm. Even when toxic doses are taken, the damage can be prevented or corrected by an increased vitamin-C intake (ref. 2, p. 36). The only food known to contain a toxic amount of this vitamin is polar-bear liver. (If you are served polar-bear liver, watch yourself.) There is little if any evidence that vitamin-A deficiencies can be more quickly overcome by taking amounts larger than 100,000 units daily; much research indicates that no more than 50,000 units per day can be well utilized. The addition of vitamin E in amounts of 100 units (not milligrams) daily has been found to double the curative effect of vitamin A. Doses of vitamin A are also more effective if taken in small amounts twice or three times daily rather than at one time. The Council on Pharmacy and Chemistry of the American Medical Association 6 has approved the following therapeutic doses: 25,000 units three times daily for prolonged or chronic deficiency; 25,000 units twice daily for two months for general treatment. They have not approved any single dose larger than 25,000 units. The amount of vitamin A needed by healthy persons varies widely with each individual. Adults require more vitamin A than do children because the vitamin is needed in proportion to body weight; men usually require more than do women. Aged persons often utilize their food less well and therefore appear to need more of most vitamins than do younger adults. The requirements also vary with intensity of light, use of eyes, season, source, amount absorbed, and intake of vitamin E. One individual may thus require two or three times more than another of the same weight and degree of health. Moreover, when the vitamin is supplied by carotene, twice as much is needed as when it is supplied by vitamin A itself. Obviously no exact rules can be laid down. Since an excess can be stored to great advantage and only massive doses are toxic, it seems wiser to err by obtaining slightly too much rather than too little. Dr. Henry C. Sherman, when at Columbia University, carried on experiments to determine the amount of vitamin A used advantageously by animals. A certain quantity of the vitamin allowed the animals all the appearances of goqd health. When that quantity was doubled, tripled, and quadrupled, signs of greater health, greater resistance, and greater vigor were evident, and with each increase the life span was lengthened. Beyond that point, increases brought no further improvements. Based on these experiments, Dr. Sherman recommends 20,000 units of vitamin A daily for adults, or four times the amount which usually gives the appearance of good health. Considering that the vitamin-A content of foods varies widely and that the absorption is undependable, I see no way by which one can be reasonably sure his vitamin-A intake is adequate without taking a supplement. I believe that recurring symptoms of vitamin-A deficiency can be expected in the majority of persons who fail to take this precaution. Any fish-liver-oil concentrate should be taken immediately after the meal containing the largest amount of fat. Capsules of vitamin-A acetate are now available which can be absorbed without the presence of fat; these may be superior to other forms. The amount of vitamin E needed to prevent the destruction of vitamin A is not known; I have recommended 50 units of vitamin E as mixed tocopherols for each 25,000 units of vitamin A. I usually recommend capsules of fish liver-oil supplying 25,000 units each; they are economical and can be taken daily, every other day or even every fifth day, depending on the amount of vitamin needed. You alone must make the choice, depending upon how high your ideals for health are.
In many books on nutrition including my own, there are tables of food analysis, giving quantities of nutrients in standard servings. Years ago I read a criticism of such tables; the writer held that they should not be published because foods grown on different soils and under different conditions, harvested, handled, and processed by different methods contained different amounts of nutrients. At the time I disagreed violently with the writer; now I agree as violently with him. When I read the statement that apricots or other foods are rich in such nutrients as vitamin A, iron and copper, my only reaction is: Which apricot? Grown where?