Weather and its effects... Why does winter depression intensify at this time?

Many people experience a decline in mood as winter continues, following weeks of cold weather and little sunshine. Some complain of fatigue, lack of energy, and low motivation, even if they are not suffering from seasonal illnesses.

Dietmar Winkler, from the University Hospital for Psychiatry and Psychotherapy in Vienna, explained that months of limited daylight deplete the body's physical and psychological reserves. He added that continued cold weather and reduced sunshine can exacerbate symptoms in those most susceptible. He also referred to what he called "disappointment," the psychological anticipation of spring contrasted with the continued cloudy and cold weather.

For his part, sleep researcher and specialist in circadian rhythm medicine Dieter Kunz from Charité University Hospital in Berlin said that humans enter an "energy-saving mode" in the fall, noting that symptoms of winter depression often appear towards the end of the season, pointing out that studies have shown a decline in the rate of serotonin secretion in the brain during the winter to about 20 to 30%.

Kuntz explained that previous research had assumed that artificial light—because it is so dim compared to natural light—had no effect on the human circadian rhythm and energy levels. "That was a mistake," Kuntz said. He and his team conducted a study on adults at a sleep laboratory in Berlin and discovered that they slept more than an hour longer in winter if given the opportunity to go to bed later.

Kountz pointed out that work and school demands do not usually adapt to seasonal changes, resulting in many people getting about an hour less sleep in winter, which he described as unhealthy and affecting performance and overall mood.

Kuntz added that deep sleep is linked to day length, while other sleep stages are affected by outside temperature. If temperatures drop below freezing, it may take about 14 days for the duration of sleep in its various stages to decrease.

In addition to the well-known seasonal symptoms, there are more severe cases classified as clinical depression, known as Seasonal Affective Disorder (SAD). According to a review published in the Journal of Psychiatric Research, the percentage of those affected ranges from 1% to 10%, depending on the region and the method of measurement, with women and young adults being more affected.