Tea, diet and ischemic stroke prevention: a case-control study in southern China

Abstract

This PhD study investigated the effects of habitual tea drinking, soy products consumption and physical activity on the risk of ischemic stroke in a population of southern China.A case-control study was conducted in southern China during 2007-2008. Patients with incident ischemic stroke and controls were recruited from three hospitals in Foshan, namely, the First People’s Hospital of Shunde, First People’s Hospital of Nanhai, and Second People’s Hospital of Foshan. Ischemic stroke cases were defined as sudden onset of a focal neurological event, with symptoms lasting for more than 24 hours and subsequent confirmation of infarction in the brain by computed tomography scan (CT) or magnetic resonance imaging (MRI), and no previous history of stroke. Controls were subjects without history or clinical evidence indicating previous stroke, and whose treatment at the outpatient department was not related to any cardiovascular disease, a malignant tumour, or diabetes. Demographic characteristics, information on frequency and duration of tea drinking, quantity of dried tea leaves and types of tea consumed, together with habitual soy food intake and other dietary intake as well as information of habitual physical activities, were obtained from participants through face-to-face interview using a structured validated and reliable questionnaire.Of the 500 eligible cases and 600 age-matched controls approached and invited to participate in the study, a total of 374 stroke patients and 464 controls were available for data analysis, representing an eventual response rate of 74.8% and 77.3%, respectively.In this study, a significant decrease in ischemic stroke risk was observed for drinking at least one cup of tea weekly (p = 0.015), when compared with infrequent or nondrinkers; the risk reduction being largest by drinking 1-2 cups of green tea or oolong tea daily. Significant inverse dose-response relationships were also found for years of drinking and the amount of dried tea leaves brewed. The adjusted odds ratios (OR) for the highest level of consumption in terms of frequency of intake, duration of drinking and average tea leaves brewed were 0.61 (95% confidence interval (CI) 0.40 to 0.94), 0.40 (95% CI 0.25 to 0.64), and 0.27 (95% CI 0.16 to 0.46), respectively.Increased consumptions of dried soybean, tofu, soymilk and total soy foods were found to be associated with reduced risks of ischemic stroke after adjusting for confounding factors. The corresponding adjusted OR (95% CI) for the highest versus lowest level (< 50 grams) of intake were 0.20 (0.09 to 0.48), 0.56 (0.36 to 0.89), 0.18 (0.06 to 0.51) and 0.23 (0.14 to 0.39), with significant dose-response relationships observed.This study also found that increased engagements in leisure time activities were associated with reduced risks of ischemic stroke after adjustment for confounding factors. A significant inverse dose-response relationship was found for total physical activity exposure, with adjusted OR 0.25 (95% CI 0.14 to 0.45) for older adults engaged in 22 or more Metabolic Equivalent Task (MET)-hours per week relative to those less than 10 MET-hours per week.The results of this PhD study suggested that long term regular tea drinking (especially drinking green tea and oolong tea), regular soy food intake and remaining physically active at old age associate with a substantially reduced risk of ischemic stroke.