Most research into the importance of folate and B12 levels has centered on seniors, and it does seem clear now that having adequate levels of these vitamins is important for maintaining cognitive functioning as you get older. Folic acid levels are of course also regarded as crucial when the brain is developing, which is why pregnant women are urged to take supplements, and why some countries fortify their bread with it. There is less research in the extensive ground between these two end-points.
A Swedish study involving 386 15-year-olds has now found that those in the top third of folic acid intake (more than 253 micrograms per day for girls and 335 for boys) performed significantly better on their school grades compared to those in the bottom third (less than 173 micrograms folic acid per day for girls and 227 for boys).
Interestingly, while homocysteine levels in the blood were initially significant, this association disappeared after other significant predictors (gender, smoking, and SES) were controlled for. Neither was a genotype linked to higher homocysteine levels (MTHFR 677 TT homozygosity) significantly related to academic achievement. Low folate and B12 levels are associated with higher homocysteine levels in the blood, and there is evidence that it is this increase in homocysteine that is the reason for the cognitive impairment seen in age-related cognitive decline. This finding, then, suggests that this is only one part of the story.
Sweden does not fortify flour with folic acid as the United States, Canada and Australia do. Folate is a B vitamin found particularly in citrus fruit, green leafy vegetables, whole-wheat bread, and dried beans and peas; however, they are often destroyed by cooking or processing.
The sum of school grades in 10 core subjects obtained in the final semester of compulsory 9 years of schooling was used as the measure of academic achievement
(2011). High Folate Intake Is Related to Better Academic Achievement in Swedish Adolescents.