Vitamin D status and the predictors of circulating T helper 1-type immunoglobulin levels in Iranian subjects with type 1 diabetes and their siblings: a case-control study.

BACKGROUND

Vitamin D status has been linked to both T helper (Th)1/Th2 balance and susceptibility to type 1 diabetes (T1D). The present study aimed to evaluate vitamin D status and its relation to Th1/Th2 balance in subjects with T1D, their siblings and unrelated healthy controls during autumn and winter 2008-2009.

METHODS

A case-control study was conducted on subjects with T1D (n(1) = 60) and two control groups comprising nondiabetic siblings (n(2) = 60) and unrelated healthy controls (n(3) = 60). Assessments of dietary intake, anthropometry, intact parathyroid hormone (iPTH) and 25(OH)D were performed. Serum levels of immunoglobulin (Ig)G(2) and IgE, as well as the IgG2/IgE ratio, were used to evaluate Th1/Th2 balance. Vitamin D status was defined based on circulating 25(OH)D as deficiency: <27.5 nm; insufficiency 27.5 ≤ 25(OH)D <50 nm; and sufficiency ≥50 nm.

RESULTS

Vitamin D status did not differ significantly among the groups. Similarly, no significant difference in 25(OH)D, iPTH, IgG(2), IgE and IgG(2)/IgE was found. In multiple regression analysis of pooled data, PTH and body mass index were the predictors of IgG(2)/IgE. In the diabetic group, both PTH and age and, in siblings, PTH only, were the predictors of IgG(2)/IgE ratio.

CONCLUSIONS

These data suggest PTH as the major predictor of immune deviance towards the Th1 response in both type 1 diabetic subjects and their siblings. Considering that the active form of vitamin D suppresses PTH production, it is hypothesised that vitamin D replenishment of just those who are genetically prone to the disease (i.e. siblings) may be regarded as a preventive measure against T1D.