New study sheds light on seasonality in mood disorders
Article adapted from a press release written by PLOS
While cooler temperatures and falling leaves may draw some to pumpkin patches and hayrides, for others, it marks the start of shorter days and less sunlight.
In a recent study conducted by Sandy Rosenthal, Jack and Pamela Egan Chair in Chemistry, and Oleg Kovtun, research assistant professor of chemistry, they found that people experiencing depressed states had lower daytime activity, and people’s daytime activity increased with longer days and more sun exposure.
The research analyzed a study conducted in Bergen, Norway using wrist-based activity sensors, which were worn by individuals with depression and those without. The results revealed the relationships between daytime physical activity, depressed state, photoperiod (the change of day length), and solar insolation (the total amount of solar radiation you experience in a day if you are outside).
Additional results suggest that the impact of solar insolation on physical activity may differ between depressed individuals and those who are not. This finding could indicate that depressed individuals exhibit an altered physiological link between energy input (i.e., solar insolation) and physical activity. Previous research in the field has found that up to 30 percent of individuals with major depressive disorder and bipolar disorder display a seasonal pattern of symptoms.
“A conservative estimate would be that about 20 percent of that is depressive disorder with a seasonal pattern,” Rosenthal said. “We found that physical activity correlated with hours of daylight (photoperiod) and the amount of solar insolation. In particular, we found that depressed subjects showed significantly lower activity that was less sensitive to changes in solar insolation. The main finding is that we developed an approach based on open-source digital tools to probe the link between how environment interacts with physical activity.”
In the study, Kovtun and Rosenthal used a quantitative approach to examine the relationship between sunlight measures obtained from NASA data and objectively measured movement activity patterns to assess the environmental factors driving seasonality in major depressive disorder and bipolar disorder.
They used motor-activity recordings collected via accelerometers, which work similarly to smart watches and measure the rate of change of the velocity of an object with respect to time, from 23 individuals with unipolar or bipolar depression and 32 individuals without depression over the course of two weeks. Participants were recruited at the University of Bergen in Norway.
According to the authors, the study presents a generalizable strategy to understand the complex interplay between sunlight, physical activity, and depressed state using open-source digital tools.
The ability to identify mood disturbances, particularly in seasonally susceptible individuals, using passive digital biomarker data offers promise in informing next-generation predictive, personalized diagnostics in mental health. A digital biomarker, such as accelerometer-derived motor activity patterns, could form the basis of an early warning system that alerts a clinician to initiate a timely intervention.
Rosenthal said in the meantime, it is better to start preparing early if you know you are affected by the seasons changing.
“The days get short very fast in Nashville in the third week of August,” Rosenthal said. “A light box—a lamp in the shape of a box that has very bright light—is essential. The most important thing to remember is that depression ends. In Nashville in the second week of January, the solar insolation really starts to tick up. Energy will change before mood, both on the way into and on the way out of depression.”
Read the study in PLOS Mental Health, and hear from Rosenthal about how her mental health challenges influence her research.