Michigan Association of Health Plans

Light, seasonal affective disorder and COVID-19

Hanne Hoffmann, assistant professor in the College of Agriculture and Natural Resources, and her colleagues in the Hoffmann Lab, study how light regulates our physiology, affects our overall well-being and mood and induces changes in brain function. As winter approaches, Hoffmann answers questions about light and seasonal affective disorder, or SAD.

What is SAD?


Seasonal affective disorder is a type of depression that is related to changes in seasons. It usually begins with less hours of sunlight in the fall and eases in spring when days gets longer. Interestingly, a small proportion of people do experience SAD in the summer. Due to the seasonality of SAD, it is commonly known as seasonal depression. Although anyone can get SAD, women experience it four times more frequently than men. At this point, it’s unclear why women are more at risk for SAD than men. Since the disorder is caused by changes in day length, the further away from the equator you live, the higher the risk of experiencing it. 

How many people have it?


Studies indicate that as many as 20% to 40% of people living at approximately the same latitude as Michigan experience some degree of SAD in the winter. However, this number could easily be reduced through lifestyle adaptations, including spending more time outside and using light therapy.

What does lack of light do to your body and how does it affect health?


Light matters because it boosts your mood and energy. To regulate your mood and physiology, light-sensing cells send light information to the brain through the optic nerve in your eye. From here, neurons in the brain further relay the light information to regulate mood and hormone release, changing physiological functions depending on the season of the year. The impact on physiological changes in response to light is more pronounced when exposed to blue and green light wavelengths than red light wavelengths. The exact mechanisms happening in the brain for light to regulate mood is poorly understood, but evidence supports that light can regulate the mood-enhancing neurotransmitter serotonin as well as the sleep-promoting hormone melatonin.

In the summer, when most people get a lot of natural light, this promotes changes in the body allowing an increased sense of well-being, more energy and good mood. In the fall, when most people spend less time outside, combined with days with less hours of sunlight, many do not get enough natural light to maintain the “feeling happy” brain signals, and start to feel sad. The onset of SAD is progressive and is therefore often overlooked.

Common signs of SAD include lack of energy, reduced motivation, trouble concentrating and feeling down as well as being grumpy, moody or anxious. You might eat more and gain weight. Your sleep quality often is reduced, and you might sleep more but still feel tired when you get up. To be appropriately diagnosed, you should see your primary care physician.

Will it be harder to deal with SAD this winter?


This is an unusual year with the COVID-19 pandemic causing increased isolation, more time indoors and increased stress. These are all risk factors for depression and SAD, which is supported by recent research evaluating depression in the summer of 2020 and found an increase in depression by more than three times. Due to the continued changes in lifestyle, increased work, family stressors and reduced social interactions, we can expect to see a significant increase in SAD this winter.

This article was originally featured in MSU Today, read more here.