American Journal of Clinical Nutrition, Vol 3, 409-417, Copyright © 1955 by The American Society for Clinical Nutrition, Inc.

Serum Vitamin A Level: A Critique of Methods and Significance

¹ From the Nutritional Chemistry Laboratory, Nutrition Branch, U. S. Public Health Service, Department of Health, Education and Welfare, Washington, D. C.

The micromethod of Bessey et al.¹ for serum vitamin A has been shown to be subject to a number of errors. The primary difficulty arises from the fact that ultraviolet light not only destroyed vitamin A but changed other substances that absorb at 328 mµ. The results secured by the above method did not agree with those from another spectrophotometric method. The differences were especially large for those serum samples containing low levels of vitamin A.

A survey of vitamin A studies with human beings shows that the serum vitamin A level is a characteristic of the individual to a greater extent than it is a reflection of the vitamin A intake. A number of physiological alterations result in large changes in the serum vitamin A levels. Furthermore, when the vitamin A intake is reduced, changes in serum vitamin A levels occur only after the deficiency state has become very prominent. Serum carotene levels are more responsive in adults to changes in the intake of vitamin A precursors (the primary source of vitamin A in adults).

The difficulties inherent in the various analytical methods for estimating vitamin A in the serum and the poor relationship between the level of that nutrient in the serum and nutritional status of the individual make the serum vitamin A level an unreliable measure of vitamin A nutritional status of either individuals or groups. The determination of the serum carotene level appears to be the procedure of choice for vitamin A studies with human beings.