Lifestyle and cancer-a joint pairwise association of lifestyle habits with subsequent cancer diagnosis.

Background: Unhealthy behaviours increase cancer risk. However, lifestyle habits co-occur and their joint association with cancer is not known.

Methods: A survey among midlife employees included data on lifestyle habits and covariates (N = 8960, response rate 67%, 80% women). The joint variables of lifestyle habits were prospectively linked with register data on cancer diagnosis (mean follow-up time 12.1 years). Cox proportional hazard model was used to calculate hazard ratios (HR), and their 95% confidence intervals.

Results: Smoking was associated with subsequent cancer risk and the association was strengthened by inactivity (HR 1.94, 1.46-2.59) and unhealthy diet (HR 1.92, 1.43-2.57). Smoking combined with both low (HR 1.70, 1.19-2.41) and moderate (HR 1.68, 1.27-2.23) alcohol consumption was also associated with increased cancer risk, as was unhealthy diet combined with moderate alcohol consumption (HR 1.55, 1.17-2.06) and inactivity (HR 1.44, 1.10-1.88). Inactivity combined with either low (HR 1.44, 1.06-1.96) or moderate (HR 1.47, 1.11-1.95) alcohol use was associated with subsequent cancer risk.

Conclusions: Key unhealthy behaviours have additive effects. Preventive measures should be targeted to especially smokers and those having several adverse lifestyle habits.