title: Smoking is associated with reduced risk of autoimmune diabetes in adults contrasting with increased risk in overweight men with type 2 diabetes: a 22-year follow-up of the HUNT study.
abstract: OBJECTIVE
  To investigate the association between smoking habits and risk of autoimmune diabetes in adults and of type 2 diabetes.
  
  
  METHODS
  We used data from the three surveys of the Nord-Trøndelag Health Study, spanning 1984-2008 and including a cohort of 90,819 Norwegian men (48%) and women (52%) aged ≥20 years. Incident cases of diabetes were identified by questionnaire and classified as type 2 diabetes (n = 1,860) and autoimmune diabetes (n = 140) based on antibodies to glutamic decarboxylase (GADA) and age at onset of diabetes. Hazard ratios (HRs) adjusted for confounders were estimated by Cox proportional hazards regression models.
  
  
  RESULTS
  The risk of autoimmune diabetes was reduced by 48% (HR 0.52 [95% CI 0.30-0.89]) in current smokers and 58% in heavy smokers (0.42 [0.18-0.98]). The reduced risk was positively associated with number of pack-years. Heavy smoking was associated with lower levels of GADA (P = 0.001) and higher levels of C-peptide (964 vs. 886 pmol/L; P = 0.03). In contrast, smoking was associated with an increased risk of type 2 diabetes, restricted to overweight men (1.33 [1.10-1.61]). Attributable proportion due to an interaction between overweight and heavy smoking was estimated to 0.40 (95% CI 0.23-0.57).
  
  
  CONCLUSIONS
  In this epidemiological study, smoking is associated with a reduced risk of autoimmune diabetes, possibly linked to an inhibitory effect on the autoimmune process. An increased risk of type 2 diabetes was restricted to overweight men.
authors.affiliation: Department of Epidemiology, Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden. bahareh.rasouli@ki.se
authors.forename: Bahareh
authors.initials: B
authors.lastname: Rasouli
authors.forename: Valdemar
authors.initials: V
authors.lastname: Grill
authors.forename: Kristian
authors.initials: K
authors.lastname: Midthjell
authors.forename: Anders
authors.initials: A
authors.lastname: Ahlbom
authors.forename: Tomas
authors.initials: T
authors.lastname: Andersson
authors.forename: Sofia
authors.initials: S
authors.lastname: Carlsson
mesh_terms: D000328:Adult; D003922:Diabetes Mellitus, Type 1 / Q000453:epidemiology* / Q000209:etiology*; D003924:Diabetes Mellitus, Type 2 / Q000453:epidemiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D050177:Overweight / Q000453:epidemiology*; D012907:Smoking / Q000009:adverse effects*; D055815:Young Adult