Wrist activity trackers used by both depressed and non-depressed individuals over two weeks highlighted the link between sunlight exposure and physical activity, as revealed by a recent study.
A recent study published on September 25, 2024, in the open-access journal PLOS Mental Health by Oleg Kovtun and Sandra Rosenthal from Vanderbilt University, explored how wrist-based activity sensors worn by people with depression and those without provided insights into the connection between daily sunlight exposure and physical activity.
Mood disorders are the top cause of disability globally. Approximately 30 percent of people with major depressive disorder and bipolar disorder show symptoms that change with the seasons, a fact now included in official diagnostic criteria. However, the effects of daylight duration (photoperiod) and sunlight intensity (solar insolation) on the seasonal variations of these disorders are not well understood.
In their study, Kovtun and Rosenthal employed a quantitative method to analyze how sunlight levels relate to more objectively measured physical activity patterns. They gathered motor activity data through accelerometers from 23 participants with unipolar or bipolar depression and 32 participants without depression, all recruited from the University of Bergen in Norway.
The results highlighted significant correlations between daytime physical activity, depressive state, photoperiod, and solar insolation. Notably, individuals experiencing more severe depression reported lower levels of daytime activity. Conversely, increased daytime activity was linked to greater photoperiod and solar insolation. Additionally, the research indicates that the effect of solar insolation on physical activity may differ between those with depression and those without. This suggests a possible disruption in how depressed individuals physiologically connect energy intake from sunlight to their levels of physical activity. Alternatively, it may reflect that increased inactivity leads to less time spent outdoors, preventing depressed individuals from benefiting from sunlight exposure.
The authors state that the study employs a broadly applicable strategy to explore the intricate relationship between sunlight, physical activity, and depressive states using accessible digital resources. Identifying mood disorders, especially in those prone to seasonal fluctuations, through passive digital biomarkers could play a key role in developing advanced predictive and personalized mental health diagnostics.
In fact, a digital biomarker such as activity patterns derived from accelerometers could help form an early warning system for clinicians to provide timely interventions. Utilizing markers for objectively measured sunlight exposure, like NASA’s solar insolation data or accelerometer-recorded light exposure, could enhance the accuracy of these predictive tools and support personalized approaches for individuals susceptible to seasonal mood disorders.
Rosenthal and Kovtun emphasize, “People with seasonal mood disorders might not yet fully recognize the patterns of their illness. One aim of our research is to encourage the creation of digital tools that aid clinicians and help individuals manage their symptoms effectively.”
