Obesity is associated with lower total serum 25-hydroxycholecalciferol (S-25OHD) concentration. However, the impact of obesity on free S-25OHD is inadequately studied. A direct assay for free 25OHD was introduced recently.

The aim of the study was to evaluate differences in vitamin D metabolism between young adults with severe childhood-onset obesity and normal-weight controls. Half of the obese subjects and controls will receive placebo and the other half will receive vitamin D3 50 µg daily for 12 weeks.

Inclusion Criteria:

• weight-for-height ratio exceeding 60% before the age of 7 years, according to Finnish growth standards and persistence of severe obesity for at least three years in childhood
• referral to the Children's Hospital, Helsinki University Hospital due to severe obesity
• at the age of 7 years lived in the greater Helsinki area

Exclusion Criteria:

• endocrine or genetic disorders underlying obesity (e.g. Prader Willi syndrome, pseudohypoparathyroidism, hypothyroidism, hypercortisolism, diabetes