Background There is a growing interest in understanding the connection between mental illness (MI) and the onset of new physical illnesses among previously physically healthy individuals. Yet the role of gender is often forgotten in research focused on comorbidity of health problems. The objective of this study was to examine gender differences in the onset of physical illness in a cohort of respondents who met criteria for MI compared with a control cohort without mental health problems.

Methods This cohort study, conducted in Ontario, Canada, used a unique linked dataset with information from the 2000–2001 Canadian Community Health Survey and medical records (n=15 902). We used adjusted Cox proportional survival analysis to examine risk of onset of four physical health problems (chronic obstructive pulmonary disorder, asthma, hypertension and diabetes) for those with and without baseline MI across a 10-year period (2002–2011) among respondents aged 18–74 years. We controlled for socioeconomic and health indicators associated with health.

Results The incidence of physical illness in the MI cohort was 28.5% among women and 29.9% among men (p=0.85) relative to controls (23.8% and 24%, respectively; p=0.48). Women in the MI cohort developed secondary physical health problems a year earlier than their male counterparts (p=0.002). Findings from the Cox proportional survival regression showed that women were at 14% reduced risk of developing physical illness, meaning that men were more disadvantaged (HR=0.89, CI 0.80 to 0.98). Those in the MI cohort were at 10 times greater risk of developing a secondary physical illness over the 10-year period (HR=1.10, CI 0.98 to 1.21). There was no significant interaction between gender and MI cohort (HR=1.05, CI 0.85 to 1.27).

Conclusions Policy and clinical practice have to be sensitive to these complex-needs patients. Gender-specific treatment and prevention practices can be developed to target those at higher risk of multiple health conditions.