Responsiveness of dark-adaptation threshold to vitamin A and beta-carotenesupplementation in pregnant and lactating women in Nepal

Background: Impaired dark adaptation occurs commonly in vitamin A deficienc y. Objective: We sought to examine the responsiveness of dark-adaptation thres hold to vitamin A and beta-carotene supplementation in Nepali women. Design: The dark-adapted pupillary response was tested in 298 pregnant wome n aged 15-45 y in a placebo-controlled trial of vitamin A and beta-carotene ; 131 of these women were also tested at 3 mo postpartum. Results were comp ared with those for 100 nonpregnant US women of similar age. The amount of light required for pupillary constriction was recorded after bleaching and dark adaptation. Results: Pregnant women receiving vitamin A had better dark-adaptation thre sholds (-1.24 log cd/m(2)) than did those receiving placebo (-1.11 log cd/m (2): P = 0.03) or beta-carotene (-1.13 log cd/m(2); P = 0.95) (t tests with Bonferroni correction). Dark-adaptation threshold was associated with seru m retinol concentration in pregnant women receiving placebo (P = 0.001) and in those receiving beta-carotene (P = 0.003) but not in those receiving vi tamin A. Among women receiving placebo, mean dark-adaptation thresholds wer e better during the first trimester (- 1.23 log cd/m(2)) than during the se cond and third trimesters (-1.03 log cd/m(2); P = 0.02, t test). The mean t hreshold of nonpregnant US women (-1.35 log cd/m(2)) was better than that o f all 3 Nepali groups (P < 0.001, t test, for all 3 groups). Conclusions: During pregnancy, pupillary dark adaptation was strongly assoc iated with serum retinol concentration and improved significantly in respon se to vitamin A supplementation. This noninvasive testing technique is a va lid indicator of population vitamin A status in women of reproductive age.