Vitamin A Deficiency: A Field Study in Newfoundland and Labrador

Abstract

The incidence of vitamin A deficiency was surveyed by visual methods in an area from which epidemic night-blindness has been reported. With a specially designed portable adaptometer, the threshold of the completely dark adapted eye was measured. Rise of this threshold above a “normal range” proved inadequate as an index of deficiency. Deficiency is indicated reliably by a vitamin A-labile threshold—one that, whatever its initial level, is lowered at least 0.3 logarithmic unit within 2 weeks of regular vitamin A supplementation. In practice a threshold which reacted to vitamin A usually did so within 1–6 hours. Vitamin A-labile thresholds were found in 9.7%, and clinical night-blindness in at most 3% of the subjects. About half the A-labile thresholds were within the “normal range”. About half were found in subjects suffering also from beriberi. Vitamin A-labile thresholds and beriberi are mutually independent. Acute beriberi may be accompanied by normal thresholds, stable to vitamin A. In subjects with both deficiencies, brewer's yeast does not lower the threshold, while vitamin A alone is as effective as vitamin A and brewer's yeast together. Both vitamin A deficiency and beriberi are most prevalent in February and March. Both (infants excluded) are found principally in adults. Vitamin A deficiency occurs in both sexes at average age about 26, beriberi primarily in males of average age about 40.