Fat least the darkening days of autumn bring something more than the annual ritual of resurrecting wool sweaters and cranking up the central heating. The evenings draw near and the mornings become gloomy, the energy wanes and a heavy sadness sets in.
Although seasonal affective disorder (SAD) was only officially recognized by psychiatrists in the 1980s, the connection between the seasons, mood and vitality has been observed for a long time.
The Yellow Emperor's Classic of Medicine is a Chinese text dating back to around 300 BC. – describes how the seasons affect all living things. It advised in winter to “go to bed early and get up with the sunrise,” keeping “desires and mental activity in peace and restraint, as if keeping a happy secret.”
Today, scientists are rediscovering how closely our biology is tied to the seasons. According to Dr Katie Weiss, Provost's Research Fellow at the University of Edinburgh, the biggest development over the past decade “has been the realization that seasonal changes in human mood are probably endogenous – that they are part of our physiology.”
Large scale resources such as UK Biobank transformed this field of research, allowing scientists to track seasonal patterns among hundreds of thousands of people over many years—something that was previously impossible.
However, where to draw the line between normal winter lethargy and clinical depression is not easy. Sadness is considered a subtype of major depression or bipolar disorder, defined by a predictable seasonal pattern: symptoms typically begin in the fall or winter and resolve in the spring. In addition to the typical signs of depression, people often sleep longer, feel sluggish, and want to eat more, especially carbohydrates.
The reasons for these changes are still being studied, but they are almost certainly related to decreased daylight. Light is a key regulator of our internal body or circadian clock, influencing the timing of hormone release, alertness and mood. Without enough daylight – especially when combined with too much artificial light in the evenings – these rhythms can become out of sync with the outside world.
Some people may be more sensitive to this shift than others. Weiss and her colleagues are studying seasonal effects in bipolar disorderwhere manic episodes often peak in the spring and depression is more common in the darker months. “We suspect that people with bipolar disorder may be very sensitive to light and seasonal cues, and this triggers their symptoms,” Wise said.
Even among those who don't have clinical depression, many people experience a more mild seasonal mood swing known as subsyndromal sadness or the “winter blues.” In the UK, around one in five people suffer from the condition, although only around 2% suffer from full SAD.
However, seasonal biology goes far beyond mood. Researchers have found fluctuations in expression more than 4000 protein-coding genes in white blood cells and fat, as well as changes in the cellular composition of the blood itself throughout the year.
Weiss and her colleagues recently analyzed four years of UK Biobank sleep data from half a million people. “We found that in winter people tended to sleep longer and suffer from insomnia – their sleep was not as good as in summer,” said Wise, who will present the findings at the British Sleep Society conference in Brighton next week.
As natural as these seasonal changes may be, society still expects people to carry on as usual. Few of us can hibernate, no matter how tempting it may sound. The most effective antidote to the winter slump is light. Bright light therapy remains the gold standard treatment for SAD, although timing and dosage are critical (see below). For those who cannot perform daily sessions in front of a light box, natural sunlight is a powerful substitute.
Studies of Amish communities in the United States, which spend more time outdoors and less time exposed to bright artificial light at night, show some of the lowest SBP rates reported among Caucasian populations. In contrast, the prevalence in New York City is about 4.7%.
Exposure to bright natural light early in the day helps synchronize the circadian clock and suppress the production of melatonin, a nighttime hormone that can make you sleepy. Light also has a direct warning effect: one study found that an hour of blue light increased reaction time more than the equivalent of two cups of coffee.
But light is not everything. Cognitive behavioral therapy adapted for patients with sadness may be as effective as light therapyhelping people rethink their relationship with winter rather than just managing symptoms.
Winter will come anyway. By changing our attitude, we can bring back some joy from the dark months.
.jpg.png?w=150&resize=150,150&ssl=1 "Your Weekly Horoscope: December 21 to 27, 2025")
