Body mass index and risk of tuberculosis and death

Background: High BMI has been shown to be protective against tuberculosis (TB) among HIV-uninfected individuals, as well as against disease progression and mortality among those with HIV. We examined the effect of BMI on all-cause mortality and TB incidence among a cohort of HIV-infected adults in Soweto, South Africa. Methods: A clinical cohort of 3456 HIV-infected adults from South Africa was prospectively followed from 2003 to 2008 with regular monitoring. The primary exposure was BMI and the outcomes of interest were all-cause mortality and a newly diagnosed episode of TB. Cox proportional hazard models assessed associations with risk of mortality or incident TB. Results: Incidence rates of mortality were 10.4/100 person-years for baseline BMI of 18.5 or less, 3.6/100 person-years for baseline BMI 18.6-25, 1.7/100 person-years for baseline BMI 25.1-30, and 1.6/100 person-years for baseline BMI more than 30. Compared to those with normal BMI, overweight and obese participants had a significantly reduced risk of mortality [adjusted hazard ratio 0.59 (95% confidence interval, CI 0.40-0.87) and 0.48 (95% CI 0.29-0.80), respectively]. Incidence rates of TB by baseline BMI were 7.3/100 person-years for underweight, 6.0/100 person-years for normal, 3.2/100 person-years for overweight, and 1.9/100 person-years for obese. Compared to those with normal BMI, those with overweight and obese BMI were at a significantly reduced risk of developing TB [adjusted hazard ratio 0.56 (95% CI 0.38-0.83) and 0.33 (95% CI 0.19-0.55), respectively]. Conclusion: HIV-infected individuals with obese and overweight BMI have a significantly reduced risk of both mortality and TB, after adjusting for HAART use and CD4 cell count.