Why am I so sleepy in the fall?

Seasonal affective disorder (SAD) is a major depression with a seasonal pattern. By the latest definition in the Diagnostic and Statistical Manual of Mental Health Disorders (DSM-5), it is a disorder classified as a subset of depression. But even amongst those who do not suffer the significant mental health issues of a diagnosed SAD, fall can still be a groggy time.

Though the duration of our sleep typically increases as winter approaches, the quality of our sleep can suffer, leading to grogginess and trouble staying awake during the day — a condition known as hypersomnia [1]. In one study of 293 SAD patients on the effect of light and changing seasons, hypersomnia proved to be a far more prevalent issue (80%) than insomnia (10%). Amongst the broader population, a random sample of 1,571 individuals showed that during fall, sleep tended to increase by up to two hours relative to summer [2]. You may have already noticed yourself sleeping more in October, which is the year’s peak sleep month according to the study.

Read more : Neat little guide on sleep disorders

That low-energy feeling that arrives with fall is the natural result of fewer daylight hours, and the reduced supply of vitamin D we get from sunshine. At the same time, the lessened exposure to natural light also disrupts the body’s circadian rhythm, the internal biological process that regulates our sleep cycle regardless of our personal schedules. A 2012 study from the University of Tromsø in Norway compared the sleep patterns of subjects in two locations with very different patterns of light exposure and day length, in Accra, Ghana and Tromsø [3]. It found that exposure to daylight in the morning had a notable impact on circadian rhythm. The subjects in Ghana reported almost no seasonal differences compared to those in Norway.

Read more: Exposure to the sun during winter is insufficient to maintain a good level of vitamin D

Another study on sleep patterns amongst office workers showed that those with windowless offices, and who thus received only minimal daytime light exposure, experienced poorer overall sleep quality and reduced levels of physical activity than their counterparts who could see at least a little sunshine from their desks [4].

A decrease in light exposure increases the body’s production of melatonin, a hormone that helps regulate circadian rhythm. Increased melatonin in the body leads to sluggishness and tiredness — we may feel like we need more sleep simply due to the increased melatonin levels. At a higher level, studies in recent years have shown that our bodies tend to move serotonin, the precursor for melatonin, out of our brains more rapidly in the colder month [5] [6].

Bright-light therapy has been shown to help some patients suffering from hypersomnia, and it is also effective in treating SAD [7].

Of course, the end of daylight saving time doesn’t help matters as it forces our body to recalibrate to a changed clock. But practicing good sleep hygiene can help you get over the hump of that adjustment quickly — this means simple things like cutting out caffeine and alcohol, exercising in the early evening, or relaxing by whatever means works best for you. Eye masks can also help, as can removing electronics with glowing LEDs from the room where you sleep. Avoiding screens before bedtime also helps signal to your body that it’s time for bed.

Read more: Exposure to natural light or a light therapy lamp may be used in the treatment of seasonal depression.

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