How scientists are shedding light on the biology behind seasonal affective disorder | Mental health

For for some, the dark days of autumn bring much more than the annual ritual of reviving woolen jumpers and turning on the central heating. As the evenings draw in and the mornings grow dark, energy diminishes and a heavy sadness sets in.

Although Seasonal Affective Disorder (SAD) was only formally recognized by psychiatrists in the 1980s, the connection between seasons, mood, and vitality has long been observed.

The Yellow Emperor’s Classic of Medicine – a Chinese text dating from around 300 BC – describes how the seasons affect all living things. He advises that in winter one should “retire early and get up with the sunrise”, keeping “desires and mental activity calm and controlled, as if keeping a happy secret”.

Today, scientists are rediscovering how closely our biology is tied to the seasons. According to Dr Cathy Wyse, a researcher at the University of Edinburgh, the biggest advance of the last decade “has been the realization that seasonal changes in human mood are likely endogenous – that they are part of our physiology”.

Large-scale resources such as the UK Biobank have transformed this area of ​​research, allowing scientists to track the seasonal trends of hundreds of thousands of people over many years – something previously impossible.

However, it is not easy to draw the line between normal winter sluggishness and clinical depression. Sad is recognized as a subtype of major depression or bipolar disorder, defined by its predictable seasonal pattern: symptoms usually begin in fall or winter and disappear by spring. Besides the typical signs of depression, people often sleep longer, feel lethargic, and want to eat more, especially carbohydrates.

The triggers for these changes are still being studied, but they are almost certainly linked to a decrease in daylight. Light is the key regulator of our internal clock 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 evening – these rhythms can become out of sync with the outside world.

Some people may be more sensitive to this change than others. Wyse and his colleagues study the seasonal effects of bipolar disorder, where manic episodes often peak in the spring and depression tends to be more common during the darker months. “We suspect that people with bipolar disorder may be very sensitive to light and seasonal cues, which trigger their symptoms,” Wyse said.

Even among people without clinical depression, many people experience a milder seasonal dip in mood, known as subsyndromal sadness or “winter blues.” In the UK, it is estimated that one in five people are affected, although only around 2% experience complete sadness.

Yet seasonal biology extends far beyond mood. The researchers found fluctuations in the expression of more than 4,000 protein-coding genes in white blood cells and fat, as well as changes in the cellular composition of the blood itself over the course of the year.

Wyse and colleagues recently analyzed four years of sleep data from the UK Biobank on half a million people. “We found that in winter people tended to sleep longer and suffer more insomnia – their sleep was not as good as in summer,” said Wyse, who will present these findings at the British Sleep Society conference in Brighton next week.

As natural as these seasonal changes may be, society still expects people to continue their lives as normal. Few of us can hibernate, as tempting as it may seem. The most effective antidote to the winter crisis is light. Light therapy remains the gold standard for treating Sad, although timing and dosage are key (see below). For those who can’t handle a daily session in front of a light box, natural sunlight is a powerful substitute.

Studies of Amish communities in the United States – who spend more time outdoors and less time exposed to bright artificial light at night – show some of the lowest rates of SAD recorded among Caucasian populations. In contrast, the prevalence in New York is approximately 4.7%.

Exposure to bright, natural light early in the day helps synchronize the circadian clock and suppress lingering melatonin, a nighttime hormone that can make a person groggy. Light also has a direct alerting effect: one study found that an hour of blue-enriched light increased reaction times more than the equivalent of two cups of coffee.

But light isn’t everything. Cognitive behavioral therapy tailored to sad can be as effective as light therapy, helping people reframe their relationship with winter rather than just managing their symptoms.

Winter will come anyway. By changing the way we think about it, we can recapture some joy from the darker months.

How to beat the winter blues

• Look for the morning sun: Even in gray weather, get out as early as possible. Daylight resets your circadian clock, improves alertness and suppresses melatonin. The early morning light is particularly powerful.

• Try a light box: Brightness levels are measured in lux. A typical Sad lamp will emit light of around 10,000 lux, which is 20 to 40 times brighter than typical office lighting, and roughly equivalent to outdoor light on a cloudy summer day. Sit in front of it for 20 to 30 minutes shortly after waking up.

• Check your sleep habits: Stick to regular sleep and wake times, avoid screens late at night, and keep evening lighting warm and dim. This helps keep your internal rhythms from drifting.

• Get out – correctly: Even on cloudy days In January, outdoor light is about 10 times brighter than indoor light. Aim for at least an hour a day, ideally combining it with something pleasant: a walk, a coffee in the park or an outing with friends.

• Plan for winter fun: Reframe thoughts like “I hate winter” to “Winter is harder, but I can plan around it.” Embrace cozy rituals, like candles, hot chocolate, or warm baths, and plan social or outdoor activities, like cold water swims or winter hikes.

• Know when to ask for help: If problems with mood, sleep or motivation persist for weeks or interfere with daily life, talk to a GP or mental health professional. Sadness is treatable.