An examination of vitamin a deficiency among African natives by the visual dysadaptation test

Using a modification of the apparatus of Mutch and Griffith an investigation of the degree of visual adaptation to light has been carried out among African natives and a numerical method of recording results devised. This has been named the Dark Adaptation index (D.A. index). Poor adaptation and consequently low reserves of vitamin A were found in 93 per cent. of a group of ninety-four African natives. A higher average D.A. index and a larger proportion of normal subjects were found in pastoral and fisher tribes than in agricultural. Following the administration of vitamin A or carotene, considerable improvement was seen in the D.A. index. After treatment for a minimum of 3 weeks only 19 per cent. of the group remained subnormal while the average index rose from 15·6 to 22·4. Evidence has been produced to show that vitamin A itself exerts a more rapid and powerful action in causing the disappearance of clinical signs of vitamin A deficiency than vegetable carotene. It is suggested that vitamin A is from three to five times more potent than an oily source of carotene such as palm oil. The daily requirements of the African native have been estimated at about 3,000 i.u. of vitamin A.