Although several studies have reported an association between blood folate concentrations and depressive symptoms, few studies have prospectively examined the association. This study aimed to investigate the cross-sectional and prospective associations between serum folate concentrations and depressive symptoms among Japanese. We analysed data among 545 subjects who participated in a health survey at the time of periodic check-up in 2009 for a cross-sectional association and among 272 subjects without depressive symptoms at baseline (in 2006) who responded to both baseline (2006) and follow-up (2009) surveys for prospective association. Depressive symptoms were assessed using the Center for Epidemiologic Studies Depression (CES-D) scale. In a cross-sectional analysis, serum folate concentrations were significantly associated with a decreased prevalence of depressive symptoms (CES-D scale of ≥16). Moreover, serum folate concentrations at baseline were significantly inversely associated with depressive symptoms after 3 years; the multivariate-adjusted odds ratios (95% confidence intervals) of depressive symptoms for the lowest through highest tertile categories of serum folate concentrations were 1.00 (reference), 0.66 (0.29-1.52) and 0.40 (0.16-0.99) (P for trend=0.047). Our findings suggest that a higher serum folate may be associated with decreased risk of depressive symptoms in Japanese.
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