title: Cigarette smoking and risk of total knee replacement for severe osteoarthritis among Chinese in Singapore--the Singapore Chinese health study.
abstract: OBJECTIVE
  Data on the effects of cigarette smoking with osteoarthritis (OA) are inconsistent and no study has examined the effect of smoking cessation. We examined smoking status, duration, dosage and cessation in association with risk of total knee replacement (TKR) for severe knee OA among elderly Chinese in Singapore.
  
  
  METHODS
  We used data from the Singapore Chinese Health Study, a population-based prospective cohort of 63,257 Chinese men and women aged 45-74 years during enrollment between 1993 and 1998. Detailed information on smoking, current diet and lifestyle factors were obtained through in person interviews. As of 31 December 2011, 1,973 incident TKR cases for severe knee OA had been identified via linkage with nationwide hospital discharge database. We used Cox regression methods to examine smoking in relation to TKR risk with adjustment for age, gender, education, body mass index (BMI), comorbidities and physical activity level.
  
  
  RESULTS
  Compared to never smokers, current smokers had a 51% decrease in risk of TKR [Hazards ratio (HR) = 0.49; 95% confidence interval (CI) = 0.40-0.60]. Among current smokers, there was a very strong dose-dependent association between increasing duration and dosage of smoking with decreasing risk of TKR (P for trend <0.0001). Among former smokers, there was a dose-dependent response between decrease in duration of smoking cessation and reduction in TKR risk (P for trend = 0.034).
  
  
  CONCLUSIONS
  Our findings strongly implicate smoking as a protective factor for TKR indicated for severe knee OA. This concurs with experimental data that nicotine promotes proliferation and collagen synthesis in chondrocytes.
authors.affiliation: Duke-NUS Graduate Medical School Singapore, Singapore; Department of Rheumatology and Immunology, Singapore General Hospital, Singapore. Electronic address: katyccc@hotmail.com.
authors.forename: Y Y
authors.initials: YY
authors.lastname: Leung
authors.affiliation: Epidemiology & Disease Control Division, Ministry of Health, Singapore.
authors.forename: L W
authors.initials: LW
authors.lastname: Ang
authors.affiliation: Duke-NUS Graduate Medical School Singapore, Singapore; Department of Rheumatology and Immunology, Singapore General Hospital, Singapore; Yong Loo Lin School of Medicine, National University of Singapore, Singapore.
authors.forename: J
authors.initials: J
authors.lastname: Thumboo
authors.affiliation: Division of Cancer Control and Population Sciences, University of Pittsburgh Cancer Institute, Pittsburgh, PA, USA.
authors.forename: R
authors.initials: R
authors.lastname: Wang
authors.affiliation: Division of Cancer Control and Population Sciences, University of Pittsburgh Cancer Institute, Pittsburgh, PA, USA; Department of Epidemiology, Graduate School of Public Health, University of Pittsburgh, Pittsburgh, PA, USA.
authors.forename: J M
authors.initials: JM
authors.lastname: Yuan
authors.affiliation: Duke-NUS Graduate Medical School Singapore, Singapore; Saw Swee Hock School of Public Health, National University of Singapore, Singapore.
authors.forename: W P
authors.initials: WP
authors.lastname: Koh
mesh_terms: D017677:Age Distribution; D000368:Aged; D019645:Arthroplasty, Replacement, Knee / Q000379:methods / Q000706:statistics & numerical data*; D044466:Asian People / Q000706:statistics & numerical data; D015331:Cohort Studies; D016001:Confidence Intervals; D016208:Databases, Factual; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D015994:Incidence; D008297:Male; D008875:Middle Aged; D020370:Osteoarthritis, Knee / Q000208:ethnology / Q000209:etiology* / Q000601:surgery*; D016016:Proportional Hazards Models; D011446:Prospective Studies; D012016:Reference Values; D018570:Risk Assessment; D012720:Severity of Illness Index; D017678:Sex Distribution; D012846:Singapore / Q000453:epidemiology; D012907:Smoking / Q000009:adverse effects* / Q000453:epidemiology; D016896:Treatment Outcome
keywords: Chinese; Cohort study; Knee osteoarthritis; Smoking