Background: An association between vitamin B12 levels and depressive symptoms (DS) has been reported in several epidemiological studies. The purpose of this study was to evaluate vitamin B12 levels in population-based samples with melancholic or non-melancholic DS as the relationship between vitamin B12 levels and different subtypes of DS has not been evaluated in previous studies.
Methods: Subjects without previously known type 2 diabetes, aged 45-74 years were randomly selected from the National Population Register as a part of the Finnish diabetes prevention programme (FIN-D2D). The study population (N = 2806, participation rate 62%) consisted of 1328 men and 1478 women. The health examinations were carried out between October and December 2007 according to the WHO MONICA protocol. The assessment of DS was based on the Beck Depression Inventory (BDI, cut-off ≥10 points). A DSM-IV- criteria based summary score of melancholic items in the BDI was used in dividing the participants with DS (N = 429) into melancholic (N = 138) and non-melancholic DS (N = 291) subgroups. In the statistical analysis we used chi-squared test, t-test, permutation test, analysis of covariance, multivariate logistic regression analysis and multinomial regression model.
Results: The mean vitamin B12 level was 331±176 pmol/L in those without DS while the subjects with non-melancholic DS had a mean vitamin B12 level of 324 ± 135 pmol/L, and those with melancholic DS had the lowest mean vitamin B12 level of 292±112 pmol/L (p < 0.001 after adjusted for age, sex, use of antidepressive medication and chronic diseases sum index). The adjusted difference of vitamin B12 levels between the non-melancholic and the melancholic group was 33 pmol/L (95%CI 8 to 57, p = 0.008). Melancholic DS and vitamin B12 levels showed an independent linearly inverse association. The relative risk ratio (RRR) for melancholic DS was 2.75 (95%CI 1.66 to 4.56) in the lowest vitamin B12 level tertile versus the highest (p for linearity <0.001) when those without DS formed the reference group. The RRR in the non-melancholic subgroup was nonsignificant.
Conclusions: The vitamin B12 level was associated with melancholic DS but not with non-melancholic DS.