Polyphenol intake and depressive symptoms in young adults: evidence from a population-based longitudinal study.

Due to the high prevalence of depression among young adults, identifying prevention strategies during young adulthood is crucial. Dietary polyphenols have been associated with depression in older cohorts; however, the association remains unclear, particularly in young adults. This study aimed to assess the prospective association between the intake of total polyphenols, polyphenol classes and polyphenol subclasses with depressive symptoms in young adults. Data from 1484 Raine Study Generation 2 participants (52·7 % female; baseline mean age (sd): 20 (0·5)) at the -20, -22, and -27 year follow-ups (n 964, 979 and 1094, respectively), with overlap across follow-ups, were used. Energy-adjusted polyphenol intake was estimated from FFQ data using our expansion of the AUSNUT 2011-13 and Phenol-Explorer to include polyphenol content data and categorised into quartiles. The primary outcome was self-reported depressive symptoms assessed via the twenty-one-item Depression, Anxiety and Stress Scale averaged across the three time points. Linear mixed-effects models were used to assess the association between the polyphenol intake exposures and depressive symptoms. Sociodemographic characteristics and lifestyle- and health-related behaviours were adjusted for. Participants in the highest quartiles for flavonol and hydroxybenzoic acid intake had lower depressive symptoms across time than participants in the lowest quartiles (flavonols (Q4 v. Q1 mean difference: -1.38; 95% CI -2.48, -0.28); hydroxybenzoic acids (Q4 v. Q1: -1.40; 95% CI -2.53, -0.27). We found no evidence of a highest v. lowest association for all other polyphenol categories. Future studies are required to investigate whether increasing polyphenol intake could protect against depression in young adults.