The Minimum Vitamin-A Requirements of Normal Adults

Abstract

The vitamin A assay values of cooked peas and cooked spinach, as determined by the rat-growth method using U.S.P. reference cod liver oil as the vitamin A standard, were found to be in excellent agreeemnt with the carotene analysis of spinach as determined by chromatographic analysis. A daily intake of approximately 47 and 57 units of vitamin A, respectively, per kilogram of body weight was necessary for the maintenance of normal dark adaptation in two normal adults when the vitamin A value of the diet was derived almost entirely from the carotene in cooked green peas. A daily intake of approximately 77, 87 and 101 units of vitamin A, respectively, per kilogram of body weight was required for the same response in three adults when the vitamin A value of the diet was derived almost entirely from the carotene in cooked spinach. For maintenance of normal dark adaptation in adults the utilization of the vitamin A values in cooked peas and cooked spinach is intermediate between those for cod liver oil and for commercial crystalline carotene dissolved in cottonseed oil. The utilization of the vitamin A value of cooked peas was better than that of cooked spinach. A daily intake of thiamin in excess of 400 to 600 international units does not appear to improve the utilization of carotene by adults nor to diminish their minimum physiologic requirement for vitamin A. A daily intake of riboflavin in excess of about 1800 to 2400 micrograms was not accompanied by increased utilization of carotene nor by diminution of the minimum physiologic requirement for vitamin A in adults. Dietary fat in an ordinary mixed diet in excess of that which provides about 30 to 35% of the total caloric intake showed no beneficial effects upon the utilization of carotene by normal adults. A marked increase or a marked decrease in exposure of the eyes of normal adults to ordinary light sources is probably not accompanied by significantly altered requirements for vitamin A.