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Responsiveness of dark-adaptation threshold to vitamin A and ß-carotene supplementation in pregnant and lactating women in Nepal^1,2,3

¹ From the Center for Human Nutrition, Department of International Health, The Johns Hopkins School of Hygiene and Public Health, Baltimore, and the Nepal Society for the Prevention of Blindness, Kathmandu, Nepal.

Background: Impaired dark adaptation occurs commonly in vitamin A deficiency.

Objective: We sought to examine the responsiveness of dark-adaptation threshold to vitamin A and ß-carotene supplementation in Nepali women.

Design: The dark-adapted pupillary response was tested in 298 pregnant women aged 15–45 y in a placebo-controlled trial of vitamin A and ß-carotene; 131 of these women were also tested at 3 mo postpartum. Results were compared 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 thresholds (-1.24 log cd/m²) than did those receiving placebo (-1.11 log cd/m²; P = 0.03) or ß-carotene (-1.13 log cd/m²; P = 0.05) (t tests with Bonferroni correction). Dark-adaptation threshold was associated with serum retinol concentration in pregnant women receiving placebo (P = 0.001) and in those receiving ß-carotene (P = 0.003) but not in those receiving vitamin A. Among women receiving placebo, mean dark-adaptation thresholds were better during the first trimester (-1.23 log cd/m²) than during the second and third trimesters (-1.03 log cd/m²; P = 0.02, t test). The mean threshold of nonpregnant US women (-1.35 log cd/m²) was better than that of all 3 Nepali groups (P < 0.001, t test, for all 3 groups).

Conclusions: During pregnancy, pupillary dark adaptation was strongly associated with serum retinol concentration and improved significantly in response to vitamin A supplementation. This noninvasive testing technique is a valid indicator of population vitamin A status in women of reproductive age.

Key Words: Vitamin A • ß-carotene • night blindness • pregnancy • lactation • pupil • dark adaptation • dark vision • night vision • Nepal • pregnant women • postpartum women

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