Dose–response relationship between body mass index and tuberculosis in China: a population-based cohort study

OBJECTIVES: This study aimed to describe and quantify the relationship between body mass index (BMI) and tuberculosis (TB) incidence. DESIGN: A population-based prospective cohort study. SETTING: Ten randomly selected communities in the southwestern mountainous region of China. PARTICIPANTS: Participants who had resided in study sites before screening for at least 6 months were eligible. Those who refused to participate or were temporary residents (who resided less than 6 months during three waves of screening) were excluded. The present research included 26 022 participants aged over 15 years for analyses. INTERVENTIONS: The cohort study conducted three rounds of TB screening from 2013 to 2015. Face-to-face surveys for participants were carried out. TB symptoms positivity suspects underwent chest X-ray and sputum smear test for diagnosis. PRIMARY OUTCOME MEASURES: The study outcome was the diagnosed active TB in the second and third rounds of screening. RESULTS: During the follow-up of 2.25 years, 43 cases developed TB in 44 574.4 person-years. The negative log-linear relationship between BMI and TB incidence was fitted (adjusted R(2)=0.76). Overweight or obese was associated with a lower risk of TB compared with normal weight (adjusted HR (aHR) 0.34, 95% CI 0.14 to 0.82). The inverse log-linear associations between continuous BMI and individual TB risk were evaluated. In subgroup analysis, the risk of TB reduced 78% in overweight or obese women (aHR 0.22, 95% CI 0.05 to 0.97), and a 64% reduction in the elderly (aHR 0.36, 95% CI 0.12 to 1.00) compared with those with normal weight, respectively. CONCLUSIONS: The study provided evidence for a negative association between BMI and TB development in Chinese adults. It suggests the inverse dose–response relationship between BMI and TB incidence, and implies an optimal cut-off point of BMI for screening strategy.