For children with low stores of two brain-power nutrients, supplements may have different, and complex, effects, a new clinical trial suggests.
Iron deficiency is the most common nutritional deficiency worldwide, affecting about 2 billion people, according to the World Health Organization.
Poor children in developing countries are at particular risk for shortfalls in iron, as well as other nutrients, including the omega-3 fats found largely in oily fish.
So the new study looked at the effects of giving 321 schoolchildren in South Africa either supplements containing iron, omega-3s or both. All of the kids had low levels of both nutrients, which are vital for children's growth and healthy brain development.
After about eight months, researchers found varied changes in the kids' memory and learning abilities.
In general, children given iron showed improvements on tests of memory and learning. That was especially true if they had outright anemia - a disorder wherein the blood's oxygen-carrying capacity is reduced, causing problems like fatigue and difficulty with concentration and memory.
For example, on a memory test, anemic kids given iron were able to recall an extra two words out of 12.
In contrast, there was no overall benefit linked to omega-3 supplements. And when the researchers zeroed in on kids with anemia, those who used omega-3s did worse than before on one test of memory.
Then there were the children with clear iron deficiency, but not anemia. Of those kids, girls who got omega-3s fared worse, while boys improved their test scores.
What it all means for kids with nutritional deficiencies is unclear, according to lead researcher Jeannine Baumgartner, of North-West University in Potchefstroom, South Africa.
One limitation of the study, she said in an email, is that the number of children in each group her team analyzed was small. There were 67 kids with anemia, for example.
Thus, "the results need to be interpreted cautiously," Baumgartner told Reuters Health in an email.
There are still a lot of questions, according to Baumgartner, whose group's findings are published in the American Journal of Clinical Nutrition.
The children in this study were 6 to 11 years old. But, Baumgartner said, animal research suggests brain deficits that take shape early in life might not be reversible.
"The question arises whether supplementation during school age might be too late to achieve beneficial effects on cognitive performance," she said.
Still, the omega-3 findings are consistent with some recent animal research. Baumgartner said her team found that in rats deficient in both iron and omega-3s, giving either supplement alone seemed to worsen the animals' memory performance. The picture was better, though, when the rats were given both iron and omega-3s.
In children, things are more complicated. Other nutritional deficiencies, as well as exposure to toxins like lead and the general effects of poverty could all dampen kids' brain development, Baumgartner pointed out.
"We believe that more research is needed to investigate the biological and functional links between nutrients essential for brain development and cognitive functioning," she said.
Since this study focused on impoverished children with low iron, and possibly other nutritional deficiencies, the results cannot be extended to children in general, according to Baumgartner.
In the U.S., recommendations call for babies to get an iron test during the first year of life to check for deficiencies. For healthy kids older than six months, the recommended iron intake varies from 7 to 15 mg of iron per day, depending on their age and sex.
There is a risk from getting too much iron and experts tell parents to ask their doctor before giving children iron supplements.
The current study was partly funded by Unilever, which makes omega-3-enriched spreads. Paul Lohmann GmbH provided the iron supplements, and Burgerstein AG provided the omega-3s.