PhD defence A. (Amy) Hofman

Summary:

Despite the well-known health benefits of physical activity, more than a quarter of the world adult population is insufficiently active. Within this thesis, I studied the association between physical activity and mental health among middle-aged and older adults, taking into account the 24-hour window of physical activity, sedentary behavior and sleep. The studies in this thesis were performed within the framework of the Rotterdam Study, a population-based cohort of adults aged 40 years and over that originated from 1990. Our results indicated that more moderate-to-vigorous physical activity was associated with less depressive symptoms when replacing sedentary behavior or sleep. We did not find an association between physical activity and anxiety symptoms. We found that more sedentary behavior or light physical activity was associated with a poorer sleep quality when replacing sleep, but not when replacing any other activities.

Also, I explored some of the potential underlying mechanisms of the association between physical activity and mental health: the association of physical activity with brain structure, and the associations of genetic factors and inflammatory markers with mental health. We demonstrated that genetic factors identified in clinical samples, are applicable to assess genetic risk for depression in a population-based setting. Based on our studies, brain health and the immune system could not be identified as relevant mechanisms on the pathway from physical activity to mental health, however, studies with longer follow-up time and more repeated measures are needed.

Altogether, the results of this thesis emphasize the need for novel and overarching approaches to study 24-hour movement behaviors and mental health. Although effect sizes were generally small, our results may be important for prevention of physical inactivity and mental health disorders.