90% of the vitamin D that our body requires can be produced in the skin when exposed to sunlight, specifically with maximum 10 minutes a day between 10:00 and 15:00 hours.
In this sense, it is beneficial to receive the sun's rays. However, the risk of skin cancer is increased considerably by constant and prolonged exposures; therefore, it should be done with moderation and protection (UV blockers) of special filters that we already find in cosmetic products.
The lack of exposure to the sun causes rickets in children (weak and soft bones such as cartilage) and osteomalacia in adults (similar condition, but with acute pain in the bones of the pelvis, lower back and legs).
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For many years the cure for these diseases was unknown, but the hard work of several scientists, in 1919, allowed to discover that the sun helped to produce Vitamin D in the skin of animals (first it was found in pigs and rats and then in humans) . Therefore, many doctors began to indicate to their patients the consumption of cod liver oil, fish and other animals that contain high rates of this vitamin.
Although it was discovered that humans produce this regulating substance of calcium levels in the body, it was still called vitamin (it is defined as a substance that the body requires but can not produce in sufficient quantities and therefore must obtain it of food), although in reality it is a molecule / hormone that must be chemically modified in the body to perform its functions.
This molecule is not only important in the development of the skeleton and in the mineralization of the bones, but also helps to regulate the pressure and prevent preclaimsia. On the other hand, its deficiency is associated with the risk of colon cancer.
Nowadays we can find vitamin D in other foods that are not necessarily bad taste oils or animal meats. Dairy products are the main ones that usually fortify with this substance.