Cigarette smoking as a risk factor for type 2 diabetes in women compared with men: a systematic review and meta-analysis of prospective cohort studies

Background Few studies have investigated the effect of smoking on type 2 diabetes in women compared with men, even though several epidemiological studies provided a clear picture of the risk among the entire population. Methods We systematically searched PubMed and Embase up to August 2017 for prospective studies that were stratified by sex with measures of the relative risk (RR) for type 2 diabetes and current smoking compared with non-smoking. The sex-specific RRs and their ratios (RRRs), comparing women with man, were pooled using random-effects models. Results Seventeen articles were identified including 20 prospective cohorts with 5 077 289 participants and 223 084 incident cases of type 2 diabetes. The pooled RRR suggested a similar risk of type 2 diabetes associated with smoking in women compared with men (RRR: 0.98, 95% confidence interval [CI]: 0.96-1.01). Furthermore, no significant sex difference in the RR was found between former smokers and those who had never smoked (RRR: 0.98, 95% CI: 0.92-1.04). Conclusions The findings of this meta-analysis indicate that female smokers had similar risk of type 2 diabetes with male smokers.