Low serum 25-hydroxyvitamin D levels are associated with depression in an adult Norwegian population.

Observational and intervention studies have suggested an association between low levels of 25-hydroxyvitamin D (25(OH)D) and depressive symptoms in several subgroups of disease and age. This study tests the hypothesis in a general population. Our data are based on 10,086 persons who participated in the sixth Tromsø study carried out in 2007-2008. Depressive symptoms were evaluated using the Hopkins Symptoms Check List 10 (SCL-10) based on answers from a questionnaire. Results were adjusted for known confounders such as age, gender, body-mass index, physical exercise, alcohol, education, marital status, kidney function and chronic disease. Results are presented for smokers (N=1966) and non-smokers (N=8120) separately as our immunoassay seems to overestimate 25(OH)D levels for smokers. Low serum 25(OH)D levels were found to be a significant predictor of depressive symptoms in both smokers and non-smokers. The association seemed to be stronger in women. The odds ratios for depression in the highest 25(OH)D quartile were 0.59 (0.39-0.89) in smokers and 0.74 (0.58-0.95) in non-smokers compared with the lowest quartile. However, no conclusions with regard to causality can be drawn due to the cross-sectional design of the study.