Hans Orru, a professor of environmental health at the University of Tartu, said the health effects of shorter days have mostly been studied in Nordic countries, but even there there is little research.

"This topic has not been researched extensively. What we can discuss, however, is seasonal mood changes. Hormones like serotonin and melatonin play a role in influencing our mood," he explained.

"As days get shorter, serotonin levels increase, and melatonin levels decrease. This impacts how alert we feel and how well we sleep. If melatonin levels are not optimal before sleep, the quality of rest deteriorates, leaving people feeling less well," he added.

Sunlight is also directly linked to the body's production of vitamin D, which falls when there is less sunlight.

Studies show that during the darker and colder seasons, people's willingness to go outside and be active decreases, the professor said. This can simultaneously weaken the immune system and reduce sleep quality.

"When it is bright outside, people are more likely to be physically active, which makes them more tired and helps them sleep better. In contrast, as physical activity declines with shorter days, appetite tends to increase," Orru said.

"We crave more energy-rich foods because it is colder. Psychology plays a significant role in how we perceive things. We feel the cold and think we need more energy. This psychological perception influences physiology, which in turn affects health and well-being," he explained.

Energy-rich foods can temporarily improve the mood but can also lead to fluctuations in glucose levels and eventually weight gain, particularly when a sedentary lifestyle accompanies the darkness.

"In spring, as days grow longer, physical activity tends to increase, and appetite decreases," Orru noted. He also highlighted research from Norway showing that children, particularly boys, are less physically active during the winter months.

Orru believes the health risks associated with shorter days and darkness can be mitigated relatively easily. "You can still exercise in the dark — most people live in cities where sports tracks are lit in the evenings. You can also go to gyms," he suggested.

Balanced nutrition, vitamin D supplements, and light therapy lamps can also help manage mood changes related to reduced daylight, Orru stressed.

SAD affects on memory and concentration

Kelli Lehto, an associate professor of neuropsychiatric genetics at the University of Tartu, said that light significantly impacts human biology. "Light cycles influence how certain substances are synthesized in our bodies, primarily hormones and neurotransmitter systems," Lehto said.

"For some people, the dark months have a particularly adverse effect. Seasonal affective disorder (SAD) can influence mood as well as brain functions like memory and concentration," she added.

To combat these challenges, Lehto highlighted the Nordic tradition of making dark seasons cozier. "People light candles, put up Christmas lights as early as October, and do not limit them to December anymore. These practices help fight the darkness and improve mood," she said.

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