Zinc supplementation might potentiate the effect of vitamin A in restoringnight vision in pregnant Nepalese women

Background: Zinc deficiency may result in abnormal dark adaptation or night blindness, a symptom primarily of vitamin A deficiency. During a placebo-c ontrolled trial in Nepal, weekly vitamin A supplementation of women reduced but failed to eliminate the incidence of night blindness during pregnancy, suggesting a role for zinc. Objective: The study examined the efficacy of daily zinc supplementation in restoring night vision of pregnant women who developed night blindness whi le routinely receiving either vitamin A, p-carotene, or placebo in a field trial. Design: Women (n = 202) who reported to be night blind during pregnancy wer e,randomly assigned in a double-blind manner, stratified on vitamin A, p-ca rotene, or placebo receipt, to receive 25 mg Zn or placebo daily for 3 wk. Thus, the 6 groups studied were as follows: p-carotene + zinc, P-carotene a lone, vitamin A + zinc, vitamin A alone (vitamin A + placebo), zinc alone ( zinc + placebo), and placebo (2 placebos: one for the vitamin A or p-carote ne study and one for the zinc study). Women underwent a clinic-based assess ment that included pupillary threshold testing and phlebotomy before and af ter supplementation. Supplement use and daily history of night blindness we re obtained at home twice every week. Results: Zinc treatment increased serum zinc concentrations, but alone (zin c alone group), failed to restore night vision or to improve dark adaptatio n. However, women in the vitamin A + zinc group who had baseline serum zinc concentrations <9.9 mu mol/L were 4 times more likely to have their night vision restored (95% CI: 1.1, 17.3) than were women in the placebo group an d tended to have a small improvement in pupillary threshold scores (by 0.21 log candela/m(2); P = 0.09). Conclusion: These data suggest that zinc potentiated the effect of vitamin A in restoring night vision among night-blind pregnant women with low initi al serum zinc concentrations.