Vitamin D is a Major Determinant of Bone Mineral Density at School Age

Background: Vitamin D insufficiency in children may have long-term skeletal consequences as vitamin D affects calcium absorption, bone mineralization and bone mass attainment.

Methodology/principal Findings: This school-based study investigated vitamin D status and its association with vitamin D intake and bone health in 195 Finnish children and adolescents (age range 7-19 years). Clinical characteristics, physical activity and dietary vitamin D intake were evaluated. Blood and urine samples were collected for serum 25-hydroxyvitamin D (25-OHD) and other parameters of calcium homeostasis. Bone mineral density (BMD) and body composition were measured with dual-energy X-ray absorptiometry (DXA). Altogether 71% of the subjects were vitamin D insufficient (25-OHD <50 nmol/L). The median 25-OHD was 41 nmol/L for girls and 45 nmol/L for boys, and the respective median vitamin D intakes 9.1 µg/day and 10 µg/day. In regression analysis, after adjusting for relevant factors, 25-OHD concentration explained 5.6% of the variance in lumbar BMD; 25-OHD and exercise together explained 7.6% of the variance in total hip BMD and 17% of the variance in whole body BMD. S-25-OHD was an independent determinant of lumbar spine and whole body BMD and in magnitude surpassed the effects of physical activity.

Conclusions/significance: Vitamin D insufficiency was common even when vitamin D intake exceeded the recommended daily intake. Vitamin D status was a key determinant of BMD. The findings suggest urgent need to increase vitamin D intake to optimize bone health in children.