Vitamin D status and insulin requirements in children and adolescent with type 1 diabetes

Vitamin D and its active form are potent immunomodulators and are known to play an important role in the glucose/insulin metabolism. Studies on type 2 diabetes mellitus (T2DM) have shown that vitamin D increases insulin efficacy; however, there are no studies that define a similar relationship in type 1 diabetes mellitus (T1DM). The aim of this study was to investigate the relation between serum vitamin D levels and the insulin requirement used in children with T1DM.

A total of 100 patients with T1DM aged 4.7-19.9 years were included in the study. Serum calcium, phosphorus, alkaline phosphatase, parathyroid hormone, 25-hydroxyvitamin D (25OHD), and 1,25-dihydroxyvitamin D were measured. A serum 25OHD level of < 10 ng/mL was accepted as vitamin D deficiency, whereas < 20 ng/mL was accepted as vitamin D insufficiency.

We found vitamin D deficiency in 28% and vitamin D insufficiency in 43% of our patients, whereas 29% had normal serum 25OHD levels. The insulin requirement of patients with a serum 25OHD level below 10 ng/mL were significantly higher than those of patients with a serum 25OHD level above 10 ng/mL (p = 0.012). This result did not change in those with diabetes duration of over 1 year. There was weak correlation between the daily insulin requirements and serum vitamin D levels (r = -0.212, p = 0.032).

We found a significantly higher insulin requirement in T1DM children with decreased serum 25OHD levels and decreased insulin sensitivity. We recommend checking the level of serum 25OHD in children with diabetes and starting treatment if it is deficient/inadequate.