What is the role of ultraviolet rays for the life of organisms?

Ultraviolet rays reduce the excitability of the sensory nerves (pain relieving effect). Under the influence of ultraviolet rays, vitamin D, which is very important for phosphorus-calcium metabolism, is formed. Under the influence of ultraviolet rays, oxidative processes in the body intensify, the absorption of oxygen by tissues and the release of carbon dioxide increases, enzymes are activated, and protein and carbohydrate metabolism improves. The content of calcium and phosphate in the blood rises. Hematopoiesis, regenerative processes, blood supply and trophism of tissues are improved. The vessels of the skin expand, blood pressure decreases, and the general biotone of the body increases.
With significant radiation, rapid fatigue, headaches, drowsiness, memory impairment, irritability, palpitations, and decreased appetite are noted.