Effect of Sun Exposure on Serum 25(OH)D Concentration of Infants Aged 7–12 Months in Indonesia

Vitamin D deficiency is mainly caused by lack of sun exposure and low intake. Data on its prevalence and optimal sun exposure in Indonesian infants, particularly aged 7–12 mo, are lacking. This randomized controlled study aimed to evaluate the effect of sun exposure on serum 25(OH)D concentration in infants in Semarang, Indonesia. Conducted between February and May 2019, the study involved 109 infants who met inclusion criteria (no congenital/chronic illness, parental consent) and excluded those with moderate to severe malnutrition, non-yellow or brown skin tone, clinically significant vitamin D deficiency, or those receiving vitamin D supplements. Intervention group received sun exposure on 50% of body surface for 5 min, three times weekly between 10:00 am and 2:00 pm for 2 mo. Serum 25(OH)D concentration were measured pre- and post-intervention, and food recall was used to assess daily intake in both groups. Pre-intervention, there was no significant difference in serum 25(OH)D concentration between intervention (mean 39.1±14.9 ng/mL) and control group (mean 38.6±15.4 ng/mL). However, post-intervention results showed a statistically significant increase in serum 25(OH)D concentration in intervention group (mean 47.9±21.9 ng/mL) compared to control group (mean 36.6±13.7 ng/mL; p=0.005). Notably, there was no significant difference in dietary vitamin D intake between two groups throughout the study. This study concluded that brief and consistent sun exposure significantly increased serum 25(OH)D concentration in infants, suggesting that sun exposure is an effective natural strategy to improve vitamin D status in this age group.