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

ObjectivesThis study aimed to describe and quantify the relationship between body mass index (BMI) and tuberculosis (TB) incidence.DesignA population-based prospective cohort study.SettingTen randomly selected communities in the southwestern mountainous region of China.ParticipantsParticipants 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.InterventionsThe 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 measuresThe study outcome was the diagnosed active TB in the second and third rounds of screening.ResultsDuring 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 R2=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.ConclusionsThe 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.