An Experimental Determination of the Minimum Vitamin A Requirements of Normal Adults

Abstract

Five adult subjects maintained on weighted diets adequate in all known food essentials except vitamin A (the average daily intake of which was not greater than 103 international units) showed unmistakable signs of impaired dark adaptation after 16, 27, 29, 39 and 124 days, respectively. Impaired dark adaptation as measured with the visual adaptometer was the earliest definite ocular abnormality observed as a result of vitamin A deficiency. The daily intake of vitamin A (in the form of cod liver oil plus the small vitamin A value supplied by the food) necessary for the maintenance of normal dark adaptation varied for the five subjects studied between the limits of 25 and 55 international units per kilogram of body weight. The daily intake of carotene (expressed in terms of international units of vitamin A) necessary for the maintenance of normal dark adaptation varied for the five subjects studied between the limits of 43 and 103 units per kilogram of body weight. The ratios of the requirements in terms of international units of carotene to the requirements in terms of international units of vitamin A in the form of cod liver oil were remarkably constant for all subjects. Unit for unit the carotene in cottonseed oil was about 50 to 60% as effective in supporting normal dark adaptation as vitamin A in the form of cod liver oil.