As the days shorten and temperatures drop, it's natural that people are likely to spend more time indoors even on sunny days. But new research has shown that by monitoring time spent in sunshine, which is also often linked to more physical activity, can have a big impact on mental wellbeing. For the more than 410 million people worldwide with mood disorders, this can be crucial in managing mental health through winter.
Seasonal affective disorder (SAD), triggered by months of reduced daylight hours, is a subtype of major depressive disorder (MDD) and bipolar disorder (BD), and can impact people in complex ways during the winter months. And for those who already suffer from mood disorders, it can take a serious toll on mental wellbeing and physical health.
To study a way in which to measure and combat SAD, Vanderbilt University researchers gave accelerometer-equipped smartwatches to 23 people with depression and 32 without mental health issues, specifically set up to track physical activity across different seasons. Because SAD becomes more prevalent the further a population is from the equator, the study's participants were recruited from the University of Bergen in Norway.
In the two-week study, they researchers discovered new insights into how sunlight, daytime physical activity and depression were intertwined, with worse depressive symptoms presenting in those with lower movement during periods of daylight. When daytime activity was boosted, participants had more sunlight exposure. Further analysis uncovered that those with pre-existing mood disorders were more likely to be less active and in turn have lower exposure to periods of sunlight, particularly in winter, making them more susceptible to the seasons impacting their mental health.
"Individuals with seasonal mood disorders may not yet recognize the pattern of their illness," the researchers noted in the study. "One of the goals of our study is to motivate the development of digital tools to assist clinicians and help affected individuals with self management of their symptoms."
The team found that people with mood disorders were more active on sunnier days, however, they also had lower physical activity during the months of shorter daylight and less intense exposure to the sun's rays (insolation). While the researchers caution that there are many reasons as to why people with a mood disorder may be less active, such as being more likely to stay indoors, they believe that monitoring movement and solar insolation levels on a wrist-worn digital biomarker device could help people be more aware of how seasons affected their moods and encourage them to do more to lessen the impact of SAD.
They also suggest that clinicians can better understand the link between sunlight, activity and mental health by incorporating this sort of personalized diagnostic tool, combined with easily available data on solar insolation levels (in this study, the team used NASA statistics for the time period).
The World Health Organization says there are now more than 350 million people with MDD, and in excess of 60 million with BP. And of these people, nearly a third have a seasonal pattern of symptom severity. This study opens the door to further insights into just how day length (photoperiod) and sun intensity can impact energy levels and help those with more severe 'winter blues' proactively improve seasonal mental wellbeing.
Previous studies have highlighted the mental and physical impact of night-shift work and people who spend more time exposed to indoor, artificial light than natural light.
The study was published in the journal PLOS Mental Health.
Source: Vanderbilt University via Medical Xpress