Vitamin D Stored in Fat Tissue During a 5-Year Intervention Affects Serum 25-Hydroxyvitamin D Levels the Following Year.

CONTEXT

Vitamin D and 25-hydroxyvitamin D [25(OH)D] are stored in adipose tissue, but the clinical relevance is uncertain.

OBJECTIVE

To evaluate changes in serum 25(OH)D and adipose tissue vitamin D levels after stopping vitamin D supplementation.

DESIGN

A prospective, double-blind cohort follow-up study.

SETTING

Clinical Research Unit at University Hospital of North Norway.

PATIENTS

Seventy-six subjects were included after participation in a 3- to 5-year prevention of type 2 diabetes study and were administered 20,000 IU of vitamin D or placebo per week.

INTERVENTION

During the 12-month follow-up period, blood samples were drawn at the beginning and after 1, 3, 6, 9, and 12 months. Fat biopsies were taken at the start and end.

MAIN OUTCOME MEASURES

Changes in 25(OH)D level in serum and 25(OH)D and vitamin D levels in adipose tissue.

RESULTS

Forty-one of 42 subjects who were given vitamin D and 33 of 34 subjects who were given placebo completed the study. At the inclusion, mean serum 25(OH)D levels were 122 and 71 nmol/L in the vitamin D and placebo groups, respectively. Serum 25(OH)D levels were significantly higher in the vitamin D group than in the placebo group throughout and were 84.5 and 73.1 nmol/L, respectively, after 12 months. In the vitamin D group, adipose tissue vitamin D levels decreased by 52% over 12 months.

CONCLUSION

Vitamin D and 25(OH)D stored in adipose tissue after 3 to 5 years of vitamin D supplementation may have a clinically relevant effect on serum 25(OH)D level the following year.