Dietary seaweed intake and depressive symptoms in Japanese adults: A prospective cohort study

Background: This prospective cohort study aimed to investigate the association between daily seaweed intake and depressive symptoms. Methods: In a prospective study conducted between 2008 and 2011, 500 Japanese adult employees aged 20-74 years participated and were included in the final analysis. Consumption of seaweed was assessed using a brief self-administered diet history questionnaire, and changes in seaweed consumption were divided into three categories (decreased, unchanged, and increased). Depressive symptoms were assessed using a Japanese version of the Self-Rating Depression Scale (SDS). Depressive symptoms were defined as an SDS score of ≥50 in the present study. Results: At the 3-year follow-up, 46 participants (9.2%) showed depressive symptoms. Multivariate analysis showed that baseline seaweed intakes were not significantly associated with the incidence of depressive symptoms (p for trend = 0.501). Conversely, odds ratios (95% CI) for depressive symptoms were lower in the participants who had higher seaweed intake than in those who had lower seaweed intake (decreased, 1.00; unchanged, 0.32 [0.13-0.81]; increased, 0.34 [0.13-0.88]; p for trend = 0.032) after adjusting for confounding factors. Conclusions: This study revealed a relationship between higher seaweed intake and a lower incidence of depressive symptoms in Japanese adults.