title: A case-control study of rheumatoid arthritis revealed abdominal obesity and environmental risk factor interactions in northern China.
abstract: BACKGROUND
  The aim of this study was to evaluate new and previously hypothesized environmental risk factors and their interaction with rheumatoid arthritis (RA).
  
  
  METHODS
  Four hundred patients recently diagnosed with RA and 400 controls frequency-matched by gender and birth year using Propensity Score Matching (PSM) were selected from northern China. Investigation was performed using self-reported data from interviewer-administered surveys. Associations between exposure variables and risk of RA were evaluated using multifactor non-conditional logistic regression.
  
  
  RESULTS
  It showed that damp localities, draft indoor, abdominal obesity (AO), and family history of RA among first-degree relatives were independent risk factors and drinking of milk was independent protective factors for RA. Besides these risk factors, in women, infrequent delivery times, early age at menopause, and late age at menarche were also independent risk factors for RA. Both the additive model and the multiplication model suggested that there was an interaction relationship between AO and damp localities (p < .001), and only the additive model suggested that there was interaction relationship between AO and no milk drinking (p < .001) in our study population. In women, there was interaction relationship between AO and damp localities (p < .001) and between AO and age at menopause (p < .001).
  
  
  CONCLUSIONS
  In northern China, damp localities, draft indoor, AO, family history of RA among first-degree relatives, and no milk drinking may be important risk factors of RA patients.
authors.affiliation: a Department of Clinical Epidemiology and Evidence-Based Medicine , The First Affiliated Hospital, China Medical University , Shenyang , China.
authors.forename: Lingyu
authors.initials: L
authors.lastname: Fu
authors.affiliation: a Department of Clinical Epidemiology and Evidence-Based Medicine , The First Affiliated Hospital, China Medical University , Shenyang , China.
authors.forename: Jianming
authors.initials: J
authors.lastname: Zhang
authors.affiliation: b Department of Internal Medicine , Shenjing Hospital, China Medical University , Shenyang , China.
authors.forename: Lei
authors.initials: L
authors.lastname: Jin
authors.affiliation: a Department of Clinical Epidemiology and Evidence-Based Medicine , The First Affiliated Hospital, China Medical University , Shenyang , China.
authors.forename: Yao
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: a Department of Clinical Epidemiology and Evidence-Based Medicine , The First Affiliated Hospital, China Medical University , Shenyang , China.
authors.forename: Saisai
authors.initials: S
authors.lastname: Cui
authors.affiliation: a Department of Clinical Epidemiology and Evidence-Based Medicine , The First Affiliated Hospital, China Medical University , Shenyang , China.
authors.forename: Meng
authors.initials: M
authors.lastname: Chen
mesh_terms: D050153:Abdominal Fat / Q000254:growth & development; D000328:Adult; D000368:Aged; D001172:Arthritis, Rheumatoid / Q000453:epidemiology*; D016022:Case-Control Studies; D002681:China; D004777:Environment; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D056128:Obesity, Abdominal / Q000453:epidemiology*
keywords: Propensity Score Matching; Rheumatoid arthritis; abdominal obesity; interaction; risk factors