Association of vitamin D deficiency and type 1 diabetes mellitus: a systematic review and meta-analysis

Some studies have suggested that vitamin D deficiency may be associated with autoimmune diseases such as type 1 diabetes mellitus (T1DM). The objectives of this review were to perform a systematic review and meta-analysis and to assess the association between vitamin D deficiency and T1DM. PubMed, Web of Science, Lilacs, and Scielo databases were used to search the articles. The eligibility criteria were cohort, case-control, or cross-sectional observational studies, which assessed the association between vitamin D deficiency and T1DM, comparing T1DM patients with control group. Cross-sectional studies that compared means of vitamin D levels between T1DM patients and control group were included in the first meta-analysis, and cross-sectional studies that compared frequency of vitamin D deficiency between T1DM patients and control group were included in the second meta-analysis. Thirteen studies were included in the systematic review. Most studies (n = 12) compared vitamin D levels between T1DM patients and control group and 75% of them (n = 9) found lower vitamin D levels in T1DM patients. Over half studies (n = 8) compared vitamin D deficiency frequency between T1DM patients and control group and 50% (n = 4) of them observed a higher frequency of vitamin D deficiency in T1DM patients. Meta-analysis demonstrated a significant difference of vitamin D levels between T1DM patients and control group (difference between means = 0.739 ± 0.067, p < 0.001) and that there is a significant association of vitamin D deficiency and T1DM [OR = 1.640 (1.18–1.28), p = 0.003]. There is a significant association between vitamin D deficiency and T1DM.