title: Lower risk of tuberculosis in obesity.
abstract: BACKGROUND
  Obesity is increasingly prevalent in both developed and developing areas. Although undernutrition is well associated with tuberculosis, few studies have systematically examined the association with obesity. Method A cohort of 42 116 individuals 65 years or older enrolled at 18 health centers for elderly patients in Hong Kong, China (which has a tuberculosis incidence of approximately 90 per 100,000 population), in 2000 were followed up prospectively through the territory-wide tuberculosis registry for the development of active tuberculosis from 3 months after enrollment until December 31, 2005, using the identity card number as the unique identifier. The association with body mass index (BMI; calculated as weight in kilograms divided by the square of height in meters), as categorized by the Asian standards, was assessed with the control of other baseline characteristics.
  
  
  RESULTS
  Obese (BMI>or=30) and overweight (BMI, 25 to <30) individuals were at significantly lower risks of developing active tuberculosis than normal-weight individuals (BMI, 18.5 to <25), with hazard ratios (95% confidence intervals) of 0.36 (0.20-0.66) and 0.55 (0.44-0.70), respectively, after adjustment for baseline demographic, social, and clinical variables. An inverse linear association was observed predominantly for pulmonary but not extrapulmonary tuberculosis. This association persisted after controlling for potential confounders or excluding individuals with known tuberculosis risk factors.
  
  
  CONCLUSIONS
  Obesity is associated with a lower risk of active pulmonary tuberculosis in the older population of Hong Kong. The presence of such a strong but selective association across the whole spectrum of BMI could have major biological, clinical, and/or epidemiological implications. Further studies are indicated to explore the underlying mechanisms, potential clinical utilities, and possible epidemiological consequences.
authors.affiliation: Tuberculosis and Chest Service, Department of Health, The University of Hong Kong, and Tuberculosis and Chest Unit, Grantham Hospital, Wanchai Chest Clinic, 99 Kennedy Rd, Wanchai, Hong Kong, China. cc_leung@dh.gov.hk
authors.forename: Chi C
authors.initials: CC
authors.lastname: Leung
authors.forename: Tai H
authors.initials: TH
authors.lastname: Lam
authors.forename: Wai M
authors.initials: WM
authors.lastname: Chan
authors.forename: Wing W
authors.initials: WW
authors.lastname: Yew
authors.forename: Kin S
authors.initials: KS
authors.lastname: Ho
authors.forename: Gabriel
authors.initials: G
authors.lastname: Leung
authors.forename: Wing S
authors.initials: WS
authors.lastname: Law
authors.forename: Cheuk M
authors.initials: CM
authors.lastname: Tam
authors.forename: Chi K
authors.initials: CK
authors.lastname: Chan
authors.forename: Kwok C
authors.initials: KC
authors.lastname: Chang
mesh_terms: D000368:Aged; D015992:Body Mass Index; D005260:Female; D005500:Follow-Up Studies; D006723:Hong Kong / Q000453:epidemiology; D006801:Humans; D015994:Incidence; D008297:Male; D009765:Obesity / Q000150:complications*; D016016:Proportional Hazards Models; D011446:Prospective Studies; D018570:Risk Assessment; D012307:Risk Factors; D017678:Sex Distribution; D015996:Survival Rate; D014376:Tuberculosis / Q000150:complications / Q000453:epidemiology*