The annual pattern of winter depression and melancholy — better known as seasonal affective disorder, or SAD — suggests a strong link between your mood and the amount of light you get during the day.
To put it simply: the less light you are exposed to, the more your mood can decline.
The winter blues are common, but about 10 million Americans are affected each year by a longer-lasting depression called seasonal affective disorder. In addition to low mood, symptoms include anxious feelings, low self-esteem, longer sleep duration, constant craving for carbohydrates, and low level of physical activity.
I am a nutritional neuroscientist and my research focuses on the effects of diet and lifestyle factors on mood and brain functions such as mental distress, resilience and motivation.
Through my research, I learned that seasonal affective disorder can strike anyone. However, people with a history of mood disorders are at higher risk. In particular, young adults and women of all ages have heightened susceptibility.
Why seasonal depression occurs
When daylight saving time ends each fall, shifting back one hour reduces the amount of light exposure most people receive in a 24-hour cycle. As the days get shorter, people may experience general mood swings or longer-term depression related to shorter exposure to daylight.
This happens due to a misalignment between the sleep-wake cycle, eating schedules, and other daily tasks. Research shows that this mismatch may be associated with poor mental health outcomes, such as anxiety and depression.
Our sleep-wake cycle is controlled by the circadian rhythm, an internal clock 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 signals from limited daylight, it releases the hormone melatonin to promote sleep – even though we still have hours before our usual bedtime. This can then affect how much energy we have, and when and how much we eat. It can also alter the brain’s ability to adapt to environmental changes. This process, called neural plasticity, involves the growth and organization of neural networks. This is crucial for the repair, maintenance and general functioning of the brain.
It is possible to readjust the circadian rhythm to better align with the new light and dark schedule. This means exposing yourself to daylight as soon as possible upon waking, as well as maintaining sleep, exercise, and eating routines more in line with your routine before the clock change. Eventually, people can gradually switch to the new schedule.
The intimate connection between serotonin and melatonin
Serotonin is a chemical messenger in the brain that plays a key role in regulating several functions such as mood, appetite, and circadian rhythm. Serotonin also converts to melatonin with lower light intensity. As mentioned above, melatonin is a hormone that regulates the sleep-wake cycle and signals the brain that it’s time to sleep.
Less exposure to daylight during the winter months leads to the conversion of serotonin to melatonin earlier in the evening because it gets dark earlier. As a result, this untimely release of melatonin causes a disruption of the sleep-wake cycle. For some people, this can cause mood swings, daytime sleepiness, and loss of appetite regulation, usually leading to unhealthy snacking. People with seasonal affective disorder often crave foods high in simple sugars, such as sweets, because there is an intimate connection between carbohydrate consumption, appetite regulation, and sleep.
Strategies for fighting the winter blues
In winter, most people leave work when it gets dark. For this reason, light therapy is generally recommended for those who suffer from seasonal affective disorder, or even shorter periods of seasonal funk.
It can be as simple as getting light shortly after waking up. Aim to get at least an hour of natural light during the early morning hours, preferably about an hour after your usual morning waking time when the circadian clock is most sensitive to light. This is true no matter what time you wake up, as long as it’s morning. For people living in northern latitudes where there is very little winter sun, light therapy boxes – which replicate outdoor light – can be effective.
You can also improve the quality of your sleep by avoiding stimulants such as coffee, tea, or large meals near bedtime. Exercising during the day is also good – it increases serotonin production and supports circadian regulation. Eating a balanced diet of complex carbohydrates and healthy proteins promotes steady production of serotonin and melatonin, and practicing downtime before bed can reduce stress.
Taking these small steps can help the circadian rhythm adjust more quickly. For the millions of people with mood disorders, it could mean happier times during what are literally the darkest days.
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