Results
The study participants included 574 TB patients and 582 healthy controls. The TB patient group and the healthy control group exhibited no difference in statistical significance (P > 0.05) in terms of sex, age, marital status, education background and alcohol drinking; while the difference in terms of BMI, smoking, history of BCG vaccination and cooking with solid fuel was statistically significant (P < 0.05); tea drinking has significant negative association with TB (OR = 0.650, P < 0.05) (Table 1).
To exclude possible confounding and explore all the determinants meantime, multivariate unconditioned logistic regression analysis was conducted by using sex, age, marital status, education background, BMI, and alcohol drinking as the covariates, smoking, history of BCG vaccination, cooking with solid fuel, and tea drinking as independent variables. Results show that tea drinking and History of BCG vaccination had a negative association with TB (OR = 0.583 and 0.598), smoking and cooking with solid fuel was the risk factor of TB (OR = 1.589 and 1.490) (Table 2).
The study was also conducted to ascertain the associations of different classes of tea on Tuberculosis. Tea leaves can be classified as black tea (fermented tea leaves), oolong (semi-fermented tea leaves) and green tea (unfermented tea leaves). The results indicate that drinking black tea, oolong and green tea almost had same negative associations with TB, with OR being 0.683, 0.674, and 0.534, respectively (P < 0.05). (Table 3)
Subjects who drank tea were categorized into three groups by monthly amount of tea drinking: 1–60 g group, 61–150 g group, and 151–300 g group, which would help investigate a dose–response relationship of tea consumption on TB. OR for 1–60 g group, 61–150 g group, 151–300 g group were 0.674, 0.619 and 0.564, respectively, with P < 0.05; trend χ test indicated a decreasing risk for TB with increased tea consumption, with P < 0.05, which showed significant dose–response relationship of tea consumption on TB (Table 4).