Association of obesity and risk of tuberculosis

A study was conducted in Shandong Province, China, to investigate the association between Body Mass Index (BMI) and primary drug-resistant tuberculosis (DR-TB) among 8,957 newly diagnosed pulmonary TB cases. This retrospective, observational analysis grouped participants into underweight, normal weight, overweight, and obese categories, then examined clinical characteristics, drug-resistance profiles, and potential risk factors associated with DR-TB.[1]

Underweight cases tended to include both younger (15–24 years) and older (>65 years) individuals, alongside higher rates of asthma and COPD but lower diabetes prevalence. Overweight and obese patients, on the other hand, were generally middle-aged (45–64 years) and displayed a heightened prevalence of diabetes, hypertension, and other comorbid conditions, such as cancer and cavities. Obese groups also showed a larger proportion of female patients.[1]

Drug-resistance patterns varied across BMI categories. While the overall proportion of DR-TB reached 18.86% in normal-weight patients, it was higher in overweight (20.38%) and obese (23.91%) individuals. Notably, obese patients showed a substantially elevated rate of MDR-TB (17.39%), compared to 11.19% in normal-weight patients. Underweight cases were especially prone to isoniazid (INH) resistance, indicating that lower BMI may be linked with selective drug-resistant patterns.[1]

Further risk analysis revealed that being overweight increased the likelihood of MDR-TB (adjusted OR ~1.54), though the effect size was borderline significant. Males and individuals with certain comorbidities emerged as important risk factors for DR-TB across multiple BMI categories, suggesting that both physiological and demographic variables could influence the development of drug-resistant strains.[1]

These findings underscore the relevance of BMI in shaping TB clinical characteristics and drug-resistance profiles. Overweight and obese patients showed notably higher proportions of both DR-TB and MDR-TB, whereas underweight patients displayed unique vulnerabilities, particularly INH resistance. By identifying the demographic and clinical risk factors most associated with DR-TB within each BMI category, the study offers valuable insights for tailoring TB control strategies and addressing specific needs among high-risk groups.[1]

Despite the recognized link between high BMI and diabetes—as well as the established role of diabetes as a risk factor for tuberculosis (TB)—epidemiological data indicate a paradoxical inverse association between obesity and TB. In study cohorts from the NHIS and NTC, individuals with higher BMI were more likely to be male, older, current users of tobacco and alcohol, have lower educational attainment, higher diabetes prevalence, and in the NHIS cohort, lower household income. Mediation analysis showed that while higher BMI significantly increased the odds of diabetes and diabetes elevated the odds of active TB, obesity itself remained directly protective: obese individuals experienced approximately a two-thirds reduction in TB risk compared to normal-weight individuals, with 71.9% reduced odds in the NHIS cohort and 67.3% in the NTC cohort. Overall, the harmful effect of high BMI mediated through diabetes was overshadowed by this strong protective effect, resulting in a net lower TB risk among obese individuals—even those who also had diabetes—compared to normal-weight peers without diabetes.[2]

These findings were robust after accounting for potential confounding factors, with baseline BMI data collection ruling out the possibility of reverse causation (in which TB-induced weight loss could falsely lower BMI). While residual confounding by socioeconomic status cannot be entirely excluded, the study results reinforce that higher BMI exerts a paradoxical yet significant protective influence against TB, counterbalancing the heightened risk posed by diabetes.[2]

References:

1. Song, W.M., Guo, J., Xu, T.T., Li, S.J., Liu, J.Y., Tao, N.N., Liu, Y., Zhang, Q.Y., Liu, S.Q., An, Q.Q. and Li, Y.F., 2021. Association between body mass index and newly diagnosed drug-resistant pulmonary tuberculosis in Shandong, China from 2004 to 2019. BMC pulmonary medicine, 21, pp.1-14.

2. Lin, H.H., Wu, C.Y., Wang, C.H., Fu, H., Lönnroth, K., Chang, Y.C. and Huang, Y.T., 2018. Association of obesity, diabetes, and risk of tuberculosis: two population-based cohorts. Clinical Infectious Diseases, 66(5), pp.699-705.