A meta-analysis of 11 randomized controlled trials was performed. The trials were conducted in India (4 trials), Thailand (2 trials), and South Africa, Indonesia, England, Croatia, and Mali (1 trial each).

In most trials, iron was given in the form of iron sulfate, providing between 2 and 60 milligrams of elemental iron. Three trials combined iron with folic acid or vitamin C, 2 trials combined iron with EPA and DHA, and 1 trial combined iron with multiple micronutrients. All but 3 trials used a placebo as the comparator. In most trials, the supplements were taken on 5 or more days per week. The intervention duration ranged from 2 to 12 months.

Iron supplementation for boosting cognitive function in school-age children Original paper