Individual and social predictors of smoking and obesity: A panel study in Germany.

This is a longitudinal study of changes in smoking behaviour as well as becoming overweight/obese (OW/OB) and the strength of their association with personal factors such as self-control, mental health, and socioeconomic status (SES) versus their connection with the behaviour of other household members. Furthermore, we investigate that in terms of roles within a household, who is more vulnerable towards the behaviour of others. We used a hybrid model that followed individual adults (person-level fixed-effect) who participated in a national representative panel survey in Germany, SOEP, between 2008 and 2016 and answered all SF-12 items (N = 6874). The count of members in a household showing the associated adverse health behaviour was the nested random-effect. Compared with other predictors, the likelihood of a person becoming OW/OB had the strongest association with the number of cohabits who were also OW/OB and it became worse as this number increased (OR 7.18, 95% CI: 2.10-24.54 and 12.44, 95% CI: 1.53-100.85, for men and women respectively, e.g. compared with being married 2.83, 95% CI: 2.28-3.53 and 1.82, 95% CI: 1.42-2.34). However, for smoking the same rapid trend was not observed. Particularly, becoming OW/OB in female (adult) children was strongly associated with the behaviour of others (compared with household head or partner). For smoking the strongest link with others was among women who were head of the household. For both behaviours, we found neither mental health nor self-control to be strong predictors. Our findings indicate that various factors do not play equal roles in changes in health behaviour and particularly for women, becoming OW/OB is strongly connected with the behaviour of others. We further discuss the potential importance of social norms that might be helpful in developing more effective policies incorporating social connections as well as norms.