Researchers have found that lack of sunlight can significantly increase not only the risk of diabetes and cardiovascular diseases but also depression, up to and including suicidal thoughts. The findings of the respective study were published in the Journal of Health Economics.

The new study showed that people who spend less time in the sun are more likely to suffer from metabolic disorders, high blood pressure, and deterioration in emotional state.

The international team of researchers links these effects to vitamin D deficiency and disruption of internal biorhythms. When sunlight is insufficient, the production of serotonin — the hormone responsible for mood — decreases, while the level of melatonin increases, causing drowsiness and apathy. And this imbalance leads to seasonal depression and, in severe cases, can raise the risk of suicide.

Researchers also discovered that, in conditions of sunlight deficiency, cells respond worse to insulin, and this increases the likelihood of developing type 2 diabetes. In addition, inflammatory processes in blood vessels increase, their elasticity deteriorates, and the risk of cardiovascular disease increases. Thus, lack of sunlight has a systemic impact — from metabolism to mental health.

The researchers emphasize that even short periods of exposure to sunlight can be beneficial: just 15–30 minutes a day are enough to maintain normal vitamin D levels and improve mood. This, however, is not about sunburn, but about natural light — walks, open windows, and morning sunrays.

The researchers hope that the new data will help revise the guidelines for preventing chronic and mental diseases, especially for residents of northern regions of the globe and for those who spend most of their time indoors.