Age-gender differences in the relationships between physical and mental health*

Previous studies have identified that smoking, exercise and breadth of social interaction mediate the strong associations between physical and mental health. However, these studies have been restricted to older populations, have not explored differences by gender, and have not considered online social interaction. We explore how the effects of four mediators (exercise, smoking, in-person and online social interaction) of the two-way relationships between past and future physical and mental health vary across eight age and gender groups. We use data from a representative sample of the UK population consisting of 175,779 observations on 41,995 adults from Understanding Society (UKHLS) between 2009 and 2019. Within a mediation framework, we estimate the percentage of the total effects that can be explained by the proposed mediating factors. We show that exercise, smoking, in-person and online social interaction are significant mediators of the effect of mental health on future physical health. In-person social interaction is the largest of these, accounting for 2.3% of the total effect. Smoking, in-person and online interaction are significant mediators of the effect of physical health on future mental health. Again, in-person interaction is the largest of these, accounting for 3.0% of the total effect. The percentages of the total effects mediated by each factor differ substantially by age and gender. Seeking to avoid the harmful effects of poor physical health on future mental health should focus on increasing physical activity in older men, and on increasing in-person social interaction in both men and women. Seeking to avoid the harmful effects of poor mental health on future physical health should focus on increasing physical activity and in-person social interaction in older men and women, and on reducing smoking in younger men and women.