Vitamin D deficiency has been shown to affect iron status via decreased calcitriol production translating to decreased erythropoiesis. The present study aimed to determine for the first time whether vitamin D supplementation can affect iron levels among Arab adolescents. A total of 125 out of the initial 200 Saudi adolescents with vitamin D deficiency [serum 25(OH)D <50nmol/l] were selected from the Vitamin D-School Project of King Saud University in Riyadh, Saudi Arabia. Cluster randomization was done in schools and allocated to receive either vitamin D tablets (1000IU/day) (N=53, mean age 14.1±1.0 years) or vitamin D-fortified milk (40IU/200ml) (N=72, mean age 14.8±1.4 years). Both groups received nutritional counseling. Anthropometrics, glucose, lipids, iron indices and 25(OH)D were measured at baseline and after 6 months. Within group analysis showed that post-intervention, serum 25(OH)D significantly increased by as much as 50% and a parallel decrease was observed in serum iron by -42% (p-values <0.001 and 0.002, respectively) in the tablet group. These changes were not observed in the control group. Between-group analysis showed a clinically significant increase in serum 25(OH)D (p=0.001) and decrease in iron (p<0.001) in the tablet group. The present findings suggest a possible inhibitory role of vitamin D supplementation in the iron indices of healthy adolescents whose 25(OH)D levels are sub-optimal but not severely deficient, implicating that the causal relationship between both micronutrients maybe dependent on the severity of deficiency, type of iron disorder and other vascular conditions which are known to affect hematologic indices. Well designed, randomized trials are needed to confirm present findings.

VITAMIN D SUPPLEMENTATION IMPROVES SERUM IRON LEVELS OF ARAB ADOLESCENT BOYS, NOT GIRLS