The annual pattern of winter depression and blues—better known as seasonal affective disorder, or SAD—suggests a strong connection between your mood and the amount of light you get during the day.
Put simply: the less light you have, the lower your mood.
The winter blues are common, but about 10 million Americans each year are affected by a longer-lasting form of depression called seasonal affective disorder. In addition to depressed mood, symptoms include feelings of anxiety, low self-esteem, prolonged sleep, persistent carbohydrate cravings, and low levels of physical activity.
I’m a nutritional neuroscientist and my research focuses on the impact of diet and lifestyle factors on mood and brain function such as mental stress, resilience and motivation.
Through my research, I’ve learned that Seasonal Affective Disorder can strike anyone. However, people with a history of mood disorders are at higher risk. In particular, susceptibility was increased in young adults of all ages and in females.
Why Seasonal Depression Occurs
Every fall when daylight saving time ends, going back one hour reduces the amount of light most people receive during the 24-hour cycle. As the days get shorter, people may experience general low mood or chronic depression, which is associated with shorter daylight exposure.
This happens due to inconsistencies between sleep-wake cycles, meal planning, and other daily tasks. Research suggests that this mismatch may be linked to adverse mental health outcomes, such as anxiety and depression.
Our sleep-wake cycles are controlled by circadian rhythms, internal clocks regulated by light and dark. Like an ordinary clock, it resets almost every 24 hours and controls metabolism, growth and hormone release.
When our brain receives the signal of limited daylight, it releases the hormone melatonin to support sleep—even when we’re hours away from our normal bedtime. This affects how much energy we have, and what and how much we eat. It can also alter the brain’s ability to adapt to changes in its environment. This process, called neuronal plasticity, involves the growth and organization of neural networks. This is essential for brain repair, maintenance and overall function.
Circadian rhythms can be readjusted to better accommodate new light and dark schedules. That means waking up to sun exposure as soon as possible, and keeping your sleep, exercise and eating habits more in sync with those you had before the time change. Eventually, people can gradually transition to the new schedule.
The Close Link Between Serotonin and Melatonin
Serotonin is a chemical messenger in the brain that is a key player in regulating mood, appetite and circadian rhythms, among other functions. Serotonin is also converted to melatonin at low light levels. As mentioned above, melatonin is a hormone that regulates the sleep-wake cycle and signals to the brain that it’s time to sleep.
Less sun exposure in winter causes serotonin to be converted to melatonin earlier in the evening because it gets dark earlier. Thus, this untimely release of melatonin causes disruptions in the sleep-wake cycle. For some, this can lead to depressed mood, daytime lethargy and loss of appetite, often leading to unhealthy snacking. People with SAD often crave simple sugar-rich foods, such as candy, because of the strong link between carbohydrate intake, appetite regulation, and sleep.
Strategies to Combat the Winter Blues
In winter, most people leave work when it gets dark. For this reason, light therapy is often recommended for those experiencing seasonal affective disorder, or, for a shorter period of time, seasonal fears.
This can be as simple as getting some light shortly after waking up. Try to get at least an hour of natural light in the early morning, preferably about an hour after your usual morning wake-up time when your body clock is most sensitive to light. This is true no matter what your wake-up time is, as long as it’s morning. For people living in northern latitudes where there is little sunlight in winter, light therapy boxes that replicate the light outside can be effective.
You can also improve sleep quality by avoiding stimulants like coffee, tea, or large meals before bed. There are benefits to exercising during the day too — it increases serotonin production and supports circadian rhythm regulation. A balanced diet of complex carbohydrates and healthy protein supports steady serotonin and melatonin production, and practicing downtime before bed can reduce stress.
Taking these small steps may help adjust your circadian rhythm more quickly. For the millions of people with mood disorders, it could mean a happier time in the darkest of days.