A new study from West Africa suggests that supplementing pregnant women's diets with extra calories and protein doesn't protect their kids against risk factors for heart disease once they're teenagers.
But researchers unconnected to the new work suggest that it might take more time for those extra prenatal calories to show up in the form of lower cholesterol and blood pressure among adult children.
"There's still such a big question mark" as to how well these supplementation programs work, said Marie-Jo Brion, an epidemiologist at the University of Bristol in the UK not tied to the study. "It's been a really difficult area to investigate."
The general theory is that kids born to moms with poor nutrition are more likely to be small and underweight at birth, which could have long-term health consequences such as heart risks, explained Dr. Prakesh Shah, an epidemiologist at the University of Toronto not involved in the new research.
In the latest study, researchers led by Sophie Hawkesworth of the London School of Hygiene and Tropical Medicine measured some of the early risk factors for diabetes and heart disease in about 1,300 Gambian kids aged 11 to 17. Half of the kids were born to mothers who were given food supplements equal to about 1,000 calories per day starting at their 20th week of pregnancy, the other half to mothers who acted as a comparison group.
But there were no clear differences between the two groups of adolescents in body mass index (a measure of weight in relation to height), cholesterol or blood pressure levels, or in blood glucose and insulin levels -- two indicators that can warn of diabetes.
In a separate trial also presented in the American Journal of Clinical Nutrition, the researchers reported that giving moms calcium during pregnancy wasn't linked to blood pressure levels in their kids between ages 5 and 10.
Shah said that it's possible the researchers need to follow kids for many more years to see a difference from the supplements, or that starting extra nutrition for moms-to-be in week 20 may be too late to have an effect on their kids' heart health.
Either way, "extrapolating these findings to a developed country is going to be a big, big challenge," Shah told Reuters Health.
"The underlying nutritional status of these mothers is completely different" than in places like the U.S. and Canada -- meaning pregnant women there shouldn't take these findings to mean that proper prenatal nutrition isn't important, he explained.
Another limitation of this study, Shah mentioned, is that the researchers were only able to track down about 60 percent of kids whose moms had been in the original study -- leaving questions about the health of those who were not included.
But Keith West, a child nutrition researcher at the Johns Hopkins Bloomberg School of Public Health, says that's par for the course with long-term studies in poor countries, and the lack of findings doesn't mean the nutrition supplements didn't make a difference.
"The endowment that occurs early in life though good nutrition is undeniable," West told Reuters Health -- including for development and disease resistance.
"In nutrition trials, these nutrients have many different effects and we often don't measure them all," he added. Plus, it's hard to predict the influence of these supplement programs because every population of moms is different in terms of their normal diet and other baseline health factors.
"Pinpointing nutritionally what's going on is difficult," Brion agreed.
Still, she said, "we would expect a lot of the studies that come out of more deprived populations to be the ones where we might see the effects of supplementation. It's a much more extreme environment."
West emphasized the importance of keeping these studies going for many years to get a better picture of how prenatal programs help kids as they grow up.
"Some interventions are going to stand out and have very clear and impressive effects, and others, in other populations, are not," he said. "It's a story in the making."