Once weekly is superior to daily iron supplementation on height gain but not on hematological improvement among schoolchildren in Thailand.

Randomized supplementation study in primary schoolchildren from two public schools in rural Songkhla Province, southern Thailand. Participants were approximately 6 to 13 years old and came from socioeconomically disadvantaged families; children with severe malnutrition, thalassemia, or severe iron deficiency anemia were excluded.

Oral ferrous sulfate 300 mg tablets providing 60 mg elemental iron were given for 16 weeks. The daily group received iron in all bottles, while the once-weekly group received iron in the Monday bottle and placebo in the remaining bottles.

Once-weekly iron was superior to daily iron for height gain over 16 weeks, while hematologic improvement was broadly similar between regimens. Hemoglobin increased in both groups, from 121.3 to 127.8 g/L with daily iron and from 121.2 to 126.9 g/L with weekly iron; both active regimens improved hemoglobin versus placebo, with P < 0.001 for daily and P = 0.026 for weekly. Daily iron produced a larger serum ferritin increase than weekly iron (39.8 vs 13.4, P < 0.001), but this did not translate into better hemoglobin or anemia outcomes. Height gain was greater with weekly than daily iron (2.6 vs 2.3 cm, P = 0.02), and no regimen notably affected weight gain, weight-for-age z-score, or height-for-age z-score.

The trial lasted only 16 weeks, so longer-term effects on growth and iron status are unknown. Generalizability is limited to rural Thai schoolchildren from disadvantaged families, and adverse events were not reported in the extracted data. Some outcomes showed modest differences, and the study does not show a clear advantage of daily dosing for clinically important hematologic endpoints.