Aims/hypothesis  

Low plasma vitamin D concentrations may promote the development of type 1 diabetes. To test this hypothesis, we measured plasma 25-hydroxyvitamin D (25OHD) in young adults with type 1 diabetes.

Methods  

The nationwide Diabetes Incidence Study in Sweden (DISS) covers 15- to 34-year-old people with newly diagnosed diabetes. Blood samples at diagnosis were collected during the 2-year period 1987/1988. Patients with islet antibodies (islet cell antibodies, GAD antibodies or tyrosine phosphatase-like protein antibodies) were defined as having autoimmune type 1 diabetes. Plasma 25OHD was measured in samples taken from 459 patients at the time of diagnosis, and in 138 of these subjects 8 years later. The results were compared with age- and sex-matched control subjects (n=208).

Results  

At diagnosis, plasma 25OHD levels were significantly lower in patients with type 1 diabetes than in control subjects (82.5±1.3 vs 96.7±2.0 nmol/l; p<0.0001). Eight years later, plasma 25OHD had decreased in patients (81.5±2.6 nmol/l; p=0.04). Plasma 25OHD levels were significantly lower in diabetic men than in diabetic women at diagnosis (77.9±1.4 vs 90.1±2.4 nmol/l; p<0.0001) and at follow-up (77.1±2.8 nmol/l vs 87.2±4.5 nmol/l; p=0.048).

Conclusions/interpretation  

The plasma 25OHD level was lower at diagnosis of autoimmune type 1 diabetes than in control subjects, and may have a role in the development of type 1 diabetes. Plasma 25OHD levels were lower in men than in women with type 1 diabetes. This difference may be relevant to the high incidence of type 1 diabetes among young adult men.