In this placebo controlled study the investigators aim to investigate the effects of vitamin D supplementation in subjects with new onset of type 1 diabetes on immunological, endocrine and metabolic parameters.

This is a bicentric, randomized placebo controlled, double blind study, with the aim to evaluate the effect of vitamin D supplementation in subjects with new onset of type 1 diabetes on immunological, endocrine and metabolic parameters.

The primary study goal is to evaluate the influence of vitamin D supplementation on the number and function of the master regulatory T-cells under controlled conditions within 13 months. The secondary study goals are a comprehensive immune phenotyping to determine whether Vit D produces changes consistent with a general improvement in immune homeostasis that supports ß-cell tolerating interventions, the assessment of ß-cell function in all subjects to obtain preliminary data on the effects of Vit D on ß-cell survival.

Inclusion Criteria:

• males or females > 6 years
• new onset of type 1 diabetes (3 months)

Exclusion Criteria:

• pregnancy
• hypercalcemia (>2,65 mmol/L)
• chronic disease including a long-term medication over 4 weeks per year (except type 1 diabetes)