AIM: To test whether a low serum 25-hydroxyvitamin D level explains the greater prevalence of depression among people with Type 2 diabetes.
METHODS: We performed a cross-sectional analysis of 527 people, aged 60-87 years, who participated in a population-based cohort study. Type 2 diabetes, impaired glucose tolerance, impaired fasting glucose and normal glucose tolerance were defined according to the 2006 WHO criteria. The Centre for Epidemiologic Studies Depression questionnaire was administered, using a cut-off score of ≥ 16 to determine clinically relevant depressive symptoms.
RESULTS: Logistic regression analysis confirmed that women with impaired glucose tolerance/impaired fasting glucose and people with Type 2 diabetes did have a higher risk of depressive symptoms [unadjusted odds ratios 3.66 (95% CI 1.59 to 8.43) and 3.04 (95% CI 1.57 to 5.88), respectively], compared with people with normal glucose tolerance. Serum 25-hydroxyvitamin D level was not a mediating factor in the association between impaired glucose tolerance/impaired fasting glucose or Type 2 diabetes and depressive symptoms [unstandardized indirect effect 0.001 (95% CI -0.063 to 0.079) and 0.004 (95% CI -0.025 to 0.094), respectively].
CONCLUSIONS: The study found no evidence that low vitamin D levels are a contributing factor to higher depression scores in people with Type 2 diabetes.