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 exposure one has, the more one’s mood may decline.

Wintertime blues are common, but about 10 million Americans are affected every year by a longer lasting depression called seasonal affective disorder. Along with low mood, symptoms include anxious feelings, low self-esteem, longer sleep duration, constant craving for carbohydrates and low physical activity levels.

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 have learned that seasonal affective disorder can strike anyone. However, people with a history of mood disorders are at a higher risk. In particular, young adults and women of all ages have an increased susceptibility.

When daylight saving time ends each fall, the one-hour shift backward reduces the amount of light exposure most people receive in a 24-hour cycle. As the days get shorter, people can experience general moodiness or a longer-term depression that is tied to a 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 darkness. Like a regular clock, it resets nearly every 24 hours and controls metabolism, growth and hormone release.

When our brain receives signals of limited daylight, it releases the hormone melatonin to support sleep – even though we still have hours left before the typical 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 changes in environment. This process, called neuronal plasticity, involves the growth and organization of neural networks. This is crucial for brain repair, maintenance and overall function.

It is possible to readjust the circadian rhythm to better align with the new light and dark schedule. This means getting daylight exposure as soon as possible upon waking up, as well as maintaining sleep, exercise and eating routines that are more in sync with your routine prior to the time change. Eventually, people can gradually transition into the new schedule.

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