Smoking Is AssociatedWith Reduced Risk of Autoimmune Diabetes in Adults ContrastingWith Increased Risk in Overweight MenWith Type 2 Diabetes

OBJECTIVEdTo investigate the association between smoking habits and risk of autoimmune diabetes in adults and of type 2 diabetes. RESEARCH DESIGN AND METHODSdWe used data from the three surveys of the Nord-Trøndelag Health Study, spanning 1984–2008 and including a cohort of 90,819 Norwe-gian 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. RESULTSdThe 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 associatedwith number of pack-years. Heavy smoking was associatedwith 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 heav