A new study from Bangladesh has experts concluding that most of the world's women don't need vitamin A supplements.
In the developing Asian nation, giving vitamin A supplements to pregnant women in the rural north didn't cut down on their chance of pregnancy-related death, or on infant deaths.
The researchers say making sure pregnant women get enough vitamin A through diet or supplements is still "an important public health goal" for other reasons.
But experts debate whether vitamin A supplements are helpful.
"At the moment I think there's very little evidence to support the supplementation of women with vitamin A," said Dr Anthony Costello, of the University College London Institute for Global Health.
"It seems likely that either it doesn't have an effect, or it only has an effect in populations where there are really serious levels of vitamin A deficiency," said Costello, who has studied vitamin A in the past but was not involved in the current research.
"For most women in the world, that probably doesn't apply."
In the Bangladeshi study, published online in the Journal of the American Medical Association, Dr Keith West of the Johns Hopkins Bloomberg School of Public Health in Baltimore and colleagues followed a population of close to 600,000 people for more than five years.
The research team identified every household in that region that had a married woman between age 13 and 45. Every 5 weeks, female staff members visited those households to find out, through discussion and urine tests, if any of the women were pregnant.
If they were, the staff began giving them a weekly dose of vitamin A, beta carotene, or a placebo every week until 12 weeks after they gave birth. The staff also gave all women educational materials about care and diet during pregnancy. The assignments to the various groups were done randomly, based on household location.
There were about 60,000 pregnancies during the study period, with mothers evenly distributed between the vitamin A, beta carotene, and placebo supplements.
A total of 138 women in the study died of any pregnancy-related cause. That worked out to 20 to 25 women per 10,000 pregnancies, regardless of what supplement they were taking.
Rates of stillbirths and infant deaths also did not vary based on the type of supplements pregnant women were given. Each supplement group had between 45 and 51 stillbirths for every 1,000 births, and between 65 and 70 infant deaths in the 12 weeks after birth per 1,000 live births.
Vitamin A deficiency has been linked with night blindness in pregnant women and with maternal death in some regions. The World Health Organisation says those risks are highest in the last three months of pregnancy. In the Bangladesh study, anyone with night blindness was treated with vitamin A, regardless of her assigned supplement.
Dr Costello, however, thinks vitamin A deficiency in the developing world has become less of a problem over the last 30 years, in the wake of economic and agricultural changes that also affect nutrition.
Previous studies, including those by Dr West and colleagues, looked at the effect of giving vitamin A to pregnant women in Ghana and Nepal and also found no effect on rates of stillbirth or infant mortality. The Nepal studies, however, did find that fewer pregnant women died when they were given vitamin A or beta carotene supplements.
Women in Bangladesh may already consume more foods rich in vitamin A compared to Nepalese women, Dr West says. They have a generally smaller chance of dying in pregnancy for other reasons too e.g., they may be more likely to have a health care worker present at their delivery.
Dr Costello said that while vitamin A deficiency is becoming less common, supplementation is still important, especially for warding off infection, in people who are deficient, including young children.
"I think you can still make a case for supplementing children," he said. "But we have to be aware that as the situation changes ... the benefits of supplementation programs may gradually decline."
And, Dr Costello said, "There's no need to go rushing off giving vitamin A to every woman in the world."
Dr West too believes nutrition is improving in many parts of the developing world, possibly making vitamin A supplementation less essential in some places, including rural Bangladesh.
"It's still a vital nutrient. If you don't have it along with other micronutrients, things will go wrong. But the dietary profiles are changing," Dr. West told Reuters Health. "Is that true everywhere? I would say no, but it's probably a general trend."
Still, he added, "We need to remain vigilant to the nutritional needs of the rural poor...in the developing world, and prevent deficiencies."
No magic bullet
Dr Prakesh Shah, who has also studied micronutrient supplements and pregnancy, takes a different message from the findings.
"Looking at one single micronutrient to have an effect on a mother dying or not dying is a little bit too much to expect," Dr Shah, a University of Toronto researcher who was not linked to the new study, told Reuters Health.
If women and babies are going to benefit from supplements, he continued, it's going to be from a supplement with more nutrients, including vitamin D, folic acid, and iron.
Maternal and infant death rates are still much higher in the developing world than in places like the U.S. and Canada. However, Dr Shah said, "Are we going to find one single bullet like vitamin A and that's going to cure all the problems? That's probably not going to happen."
(Reuters Health, Genevra Pittman, May 2011)