Physiologists: more sun means better mood and greater joy in life

The shortest day of the year, when our contact with daylight was limited to less than six hours passed on December 21. The days were getting longer. Now, in the first half of March, the day is longer than the shortest of the year by about 3.5 hours, and sun more often shines through the clouds.

Depending on the availability of sunlight, our bodies produce higher or lower levels of important hormones. One of them, melatonin, is produced in the pineal gland and regulates human circadian rhythms, including the sleep-wake cycles. "Melatonin synthesized at night extends the effective sleep time. However, exposure to sunlight increases the amount of serotonin, called +happiness hormone+" – explained in an interview with PAP Dr. Agnieszka Wsół, MD, from the Department of Experimental and Clinical Physiology at the Medical University of Warsaw.

Shortening or lengthening of day changes seasonal balance between melatonin and serotonin, indirectly leading to changes in mood. "Shorter days in the fall and winter mean increase in melatonin secretion and reduced secretion of serotonin. It is believed to be one of the causative factors of the so-called +seasonal depression+ and disturbances of circadian rhythm, sleep and wake cycle. One treatments for seasonal depression is light therapy" - noted physiologist.

When the days become longer, people feel better. "This reduces drowsiness, which bothers us in the winter season" - said Dr. Wsół, and added that after the winter we see not only an improvement in mood. "Melatonin also affects sexual behaviour. In the spring, due to the decrease in the its concentration, centers secreting sex hormones are unlocked. This is why after the winter people and animals start to feel better, start searching for partners, care about their looks and fall in love" - explained Dr. Wsół.

Mood improvement associated longer days can also indirectly benefit the immune system. "The more sun, the greater the production of serotonin. And the better we feel, the better defences the body has" - said the physiologist. At the same time, when the days become longer, we become less sluggish, we move more and less crave fat foods, for which often reach in the autumn and winter. In connection with spring circadian rhythms so we store less fat, and that can be good for the heart and circulatory system.

In addition, the availability of light is important for the bones. Under the rays of sun, provitamin D present in the skin is converted into vitamin that facilitates the absorption of calcium and phosphate and their use for building bones and teeth, normal heart rate and metabolism.

The physiologist warns against excessive exposure to the sun, because the sun\'s rays in excess "contribute to the formation of numerous DNA errors in the skin, which promotes the development of cancer". "They also accelerate aging of the skin, called skin photoaging by professionals" - noted Dr. Wsół. To take advantage of the benefits of the sun, you do not need to stay in the sun all day. A normal, slightly cloudy day is quite sufficient. Even then, a lot of radiation reaches us.

Marcin Gładysz of the Faculty of Biology and Environmental Protection, University of Silesia, added that our biological clock also responds to temperature. "The days are longer and it\'s getting warmer, which also can affect the physiology and mood. To the extent that changes not only mood, but also social interaction. When days are getting long and warm, the way of life changes: we read less, rarely watch TV and sit at the computer, we are more eager to get out of the house" - he noted.

The physiologist pointed out that man evolved from Africa, and his biological clock formed near the equator, where seasonal sunlight does not change, there are no seasons, and the length of days is almost the same all year round. "Because of this, the human body does not +understand+ phenomena such as seasons, and our behaviour does not change with the seasons in a way so simple and clear, as in animals, which after a period of hibernation start mating en masse" - he added.

In nature, seasonal cycles are much clearer. "If you look at the whole life, we see the relationship between the existence of the various cycles and availability of light and natural phenomena. Especially in the spring we see an explosion of green and the simultaneous stir among animals: birds writhing nest, spawning fish... It is a reaction of living beings to the indication of their internal biological clock, which is aligned with the seasons, and activated and calibrated by the light" - emphasised Gładysz.

He added that the human internal biological clock responds strongest to the diurnal changes in light intensity. "We are feel best when we have at least half a day exposure to light. Now, after the winter, our bodies return to normal. Finally, they get as much light as they need" - he said.

PAP - Science and Scholarship in Poland, Anna Ślązak

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