It's not often that health experts say the evidence on something is so good that it would be wrong to keep studying it. But that's exactly what a group of researchers who've reviewed 43 trials on vitamin A supplementation for young children in developing countries contend.
Their review showed that vitamin A supplements reduced child mortality by 24 percent in low and middle income countries by preventing measles, diarrhea, and vision problems in children.
In fact, starting any new trials to test vitamin A on kids – using a standard placebo vs. treatment trial – would be unethical for the kids getting the placebo, they say in a paper published Thursday in the British Medical Journal, because the benefits of vitamin A are so clear.
"I've never really seen something that works so clearly," Evan Mayo-Wilson, a lecturer at the Centre for Evidence-Based Intervention at the University of Oxford and an author of the study, tells Shots. "From the 1970s through today, the picture hasn't changed. It's striking because the evidence of a really big reduction in mortality is very consistent."
Some 190 million children around the world are deficient in vitamin A; usually these are kids whose families can't afford eggs and dairy products. A deficiency in the nutrient makes kids more vulnerable to a range of illnesses including diarrhea, measles, and respiratory infections, which could also kill them. Though vitamin A supplements have now been available for more than a decade in developing countries where the child mortality rate has fallen, the researchers say there hasn't been any direct proof that the supplements were responsible for it.
But despite the fact that most public health experts have rallied behind vitamin A supplements as an intervention that works, "no nutrient has been as well studied or as fraught with controversy," as Andrew Thorne-Lyman and Wafaie Fawzi of Harvard University note in an accompanying editorial.
A commentary published in a journal last year entitled "The great Vitamin A fiasco" helped fan the flames of doubt and attracted a lot of attention within the nutrition community. The author, Michael Latham of Cornell University, claimed that vitamin A supplementation programs don't work and don't save that many lives.
Whether Mayo-Wilson's paper will silence the critics is unclear. But in the meantime, he says, the World Health Organization and other groups that distribute vitamin A supplements need to focus on the logistical hurdles in the way of reaching more children who need them.
"Going forward it's important to pair vitamin A with other programs like vaccinations and zinc distribution," Mayo-Wilson says.