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Why does vitamin A reduce all-cause mortality of pregnant women in Nepal but not in Bangladesh?

May 19, 2011

Unlike in Nepal, vitamin A or beta-carotene supplementation has shown no effect on pregnancy-related mortality and infant mortality in Bangladesh, says a new US study.

In the randomized controlled trial, 125,257 pregnant women 13 to 45 years of age were randomly assigned to receive a weekly supplementation of either 7,000 µg vitamin A, 42 mg beta carotene, or a placebo for up to six years (1). The study results showed that vitamin A supplementation increased plasma retinol concentrations and reduced night blindness. However, supplementation did not significantly reduce all-cause maternal, fetal, or infant mortality through 12 weeks of age.

Night blindness during pregnancy, an ocular manifestation of vitamin A deficiency, is associated with increased risks of maternal anaemia, morbidity, and mortality. Preventing vitamin A deficiency (retinol concentration below 0.70 ?mol/L) could improve maternal survival. Evidence of similar effects had been reported in rural Nepal, where a randomized controlled trial demonstrated a decrease of approximately 44 percent in mortality related to pregnancy following continuous, weekly receipt of vitamin A or beta carotene during the reproductive years at dosages approximating a recommended daily allowance (2). In contrast, the trial findings for Bangladesh were neutral in that mortality was not reduced. Deficiency there was not as severe and maternal mortality risk was not so high as to be lowered further by a nutrient supplement, the researchers commented.

The scientists added that several contextual differences between the Nepalese and Bangladeshi populations studied may have been responsible for the difference in outcomes: in Bangladesh, the rate of mortality from early pregnancy through 3 months postpartum among placebo recipients was only about 30 percent of that observed among the Nepali placebo recipients. In addition, the vitamin A blood levels of Bangladeshi mothers were significantly better than those of the Nepalese women. Another key difference was that Bangladeshi mothers were more likely to have a traditional or skilled health worker attend delivery than their Nepalese counterparts.

The researchers concluded that irrespective of its effects on mortality, achieving maternal adequacy in vitamin A through diet, supplementation, or fortification is an important public health goal. For many good reasons, adequate intakes of vitamin A and its precursor beta-carotene would be essential for mother and infant.

References

  1. West K. P. et al. Effects of Vitamin A or Beta Carotene Supplementation on Pregnancy-Related Mortality and Infant Mortality in Rural Bangladesh A Cluster Randomized Trial. Journal of the American Medical Association. 2011; 305:1986–1995.
  2. West K. P. et al. Double blind, cluster randomised trial of low dose supplementation with vitamin A or
    ? carotene on mortality related to pregnancy in Nepal. BMJ. 1999; 318(7183):570–575.