Swedish teenagers who consumed more folic acid got better school grades, a small study published in the journal Pediatrics has found.

But don't run out and stock up on the B vitamin with the rest of your school supplies just yet, one expert warns.

"There is very little deficiency of folic acid in North America," Deborah O'Connor, a nutrition researcher who was not involved in the study, told Reuters Health. "If you're already sufficient, there is not a lot of evidence that taking more supplements will help."

She said the teens in the study might have been deficient in folic acid, with levels a few times lower than what's typically seen in North American kids.

Because a lack of the nutrient during pregnancy can cause severe birth defects in babies, certain foods are fortified with folic acid, also called folate, in North America. Most of the population is thought to get adequate amounts for that reason.

During the study, Sweden did not fortify foods, nor did kids use a lot of supplements. Folic acid is naturally present in green, leafy vegetables and legumes.

The new study is among the first to examine whether folate is tied to school achievements, according to Dr. Torbjorn Nilsson of Orebro University Hospital and his colleagues.

The researchers looked at 386 15-year-olds who were finishing up ninth grade. When all their grades from ten core classes were added up, there was a clear difference between teens who got the most and the least folic acid in their diets.

Teens in the top third of folic acid intake, more than 253 micrograms per day for girls and 335 for boys, scored grades of 139 out of 200, on average. Those in the bottom third, less than 173 micrograms folic acid per day for girls and 227 for boys, had an average score of only 120.
The differences remained even after the researchers accounted for gender, smoking, the mothers' education and which schools the kids went to.

O'Connor, of the University of Toronto and the Hospital for Sick Children in Ontario, Canada, called the findings "pretty significant."

Still, she said, you can't be sure if the kids who performed better had a better diet in general or if some other hidden factor could explain the results.

"It's not a randomized controlled trial, so you always wonder, are there other things going on that you weren't able to control for?" she said. "Like most studies, it probably raises more questions than it answers."

In the U.S., kids aged 9 to 13 should get a total of 300 micrograms of folate a day from food and supplements according to the Institute of Medicine's "Dietary Reference Intakes." Kids 14 and older and adults are urged to get 400 micrograms a day and pregnant women should get 600 micrograms.