Association Between Tea Consumption and Depressive Symptoms in Older Chinese Adults

Abstract

Depression is a common mental illness in elderly adults that is associated with substantial disability, medical comorbidity, and suicide risk. Factors associated with risk of depression in older adults are many, but the role of dietary and nutritional factors remains relatively unexplored. Accumulating evidence suggests that certain dietary patterns and micronutrients may have important protective effects.1-3 The present study used longitudinal data from 1,615 Chinese adults aged 55 to 93 from the Singapore Longitudinal Aging Study (SLAS)4, 5 to examine the association between amount of tea drinking and incident depressive symptoms from follow-up over an average period of 18 months. It was hypothesized that higher levels of tea consumption would be associated with lower risk of depressive symptoms at follow-up. The baseline recruitment and data collection in SLAS were completed from 2003 to 2005, and follow-up assessment of depressive symptoms was conducted from 2005 to 2007. The National University of Singapore institutional review board approved the study, and written informed consent was obtained from all participants. Trained research nurses administered the 15-item Geriatric Depression Scale (GDS-15)6 to measure depressive symptom severity. Depressive symptoms were defined as a GDS-15 total score of 5 or higher at follow-up assessment. Information on the consumption of green tea, Chinese oolong or black tea, and English black tea was collected at baseline (0 = never or rarely; 1 = <1 cup/wk; 2 = >1 cup/wk but < 1 cup/d; 3 = 1–2 cups/d; 4 = 3–5 cups/d; 5 = 6–9 cups/d; 6 = ≥10 cups/d). A participant was classified as a non-tea consumer if the sum of the scores of all three types of tea was 0. Low tea consumption was defined as a sum score from 1 to 2, medium consumption from 3 to 4, and high consumption 5 or more. Independent-sample t-tests and chi-square tests were used to compare differences in various characteristics of non-tea consumers and tea consumers and between participants with and without depression at follow-up. A variable was considered to be a potential confounder of the association between tea consumption and depressive symptoms if there was a statistically significant difference in both comparisons, and the variable was subsequently controlled for in multivariate analysis. Hierarchical multiple logistic regression was used to analyze the association between level of tea consumption and depressive symptoms at follow-up. All analyses were performed with SPSS version 19.0 (SPSS, Inc., Chicago, IL). Seventy-three participants had depressive symptoms at follow-up assessment. The proportion of participants with depression at follow-up decreased with increasing tea consumption (6.6%, 5.3%, 3.2%, and 1.8%, respectively). This linear association between tea consumption and depression was confirmed in multivariate analysis. In fully adjusted model (Table 1), the odds ratio of depressive symptoms at follow-up for participants with low, medium, and high tea consumption was 1.15, 0.55, and 0.37, respectively (P for linear trend = .01). The results remained essentially the same when all participants with cognitive impairment at baseline were excluded from the analysis. A similar linear trend of association between level of tea consumption and depressive symptoms at follow-up was observed in participants who were and were not depressed at baseline, although given small number of depression cases in each of the four categories of tea consumption, further multivariate analysis was not performed. This study provides the first evidence of a longitudinal association between tea consumption and clinically meaningful depressive symptoms in older adults. The results are consistent with an earlier report on the association between tea consumption and lower prevalence of depressive symptoms in community-living elderly adults3 and several studies that were conducted in study populations other than older adults.7, 8 These results support a cause-and-effect relationship between tea consumption and low risk of subsequent depressive symptoms. The underlying mechanisms may involve the antioxidant, anti-inflammatory, cerebrovascular protective, and antidepressant effects of bioactive compounds in tea leaves.9, 10 The role of tea consumption and tea bioactive compounds in the prevention of late-life depression deserves further study. SLAS was supported by research grants 03/1/21/17/214 and 08/1/21/19/567 from the Biomedical Research Council, Agency for Science, Technology and Research, Singapore. Conflicts of Interest: We have no financial support or relationships that may pose a conflict of interest. Author Contributions: Lei Feng formulated the hypothesis, reviewed the literature, performed the statistical analysis, and wrote the letter. Tze-Pin Ng designed the research as the principal investigator of the SLAS project. Tze-Pin Ng, Jialiang Li, Ee-Heok Kua, Tih-Shih Lee, Keng-Bee Yap, and A. John Rush reviewed the statistical analysis and revised the article. All authors read and commented on the final manuscript. Sponsor's Role: No commercial company sponsored or played any role in the design and methods of the study, participant recruitment, data collection and analysis, or preparation of this article.