It has been suggested that there are associations among insomnia symptoms and unhealthy behaviours. However, previous studies are sparse and mainly cross-sectional, and have not been focused on several key unhealthy behaviours. The aim of this study was to examine whether the associations are bidirectional, i.e. whether insomnia symptoms are associated with subsequent unhealthy behaviours, and whether unhealthy behaviours are associated with subsequent insomnia symptoms. The data were derived from the Helsinki Health Study prospective cohort study. The baseline data were collected in 2000-02 (n = 8960, response rate 67%) among 40-60-year-old employees of the City Helsinki, Finland. The follow-up data were collected in 2007 (n = 7332, response rate 83%). Logistic regression analysis was used to examine the associations among insomnia symptoms and unhealthy behaviours, including smoking, heavy and binge drinking, physical inactivity and unhealthy food habits. Frequent insomnia symptoms at baseline were associated with subsequent heavy drinking [odds ratio (OR): 1.34; 95% confidence interval (CI): 1.07-1.68] and physical inactivity (OR: 1.27; 95% CI: 1.08-1.48) after full adjustment for gender, age, corresponding unhealthy behaviour at baseline, marital status, occupational class, sleep duration and common mental disorders. Additionally, heavy drinking (OR: 1.48; 95% CI: 1.22-1.80) and binge drinking (OR: 1.26; 95% CI: 1.08-1.46) at baseline were associated with subsequent insomnia symptoms at follow-up after full adjustment. In conclusion, insomnia symptoms were associated with subsequent heavy drinking and physical inactivity, and heavy and binge drinking were also associated with subsequent insomnia symptoms.
