Mis à jour : 3 août 2020
Vitamin D is a hormone produced by skin exposure to natural sunlight, specifically the UV-B part of the light spectrum. UV means ultraviolet, which is the color beyond blue and violet. This is the high-energy end of the light spectrum. UV photons have sufficient energy to ionize molecules and break bonds.
There are several kinds of vitamin D. First, there is the D2 and D3 difference. D2 comes from plant (fungal) sources, and D3 comes mainly from animal products. Second, there is a liver conversion of calciferol (one hydroxy group) to calcidiol (two hydroxy groups), and a kidney conversion of caldidiol to calcitriol (three hydroxy groups). So vitamin D problems are fundamentally complex. Not many practitioners know how to recognize them or sleuth them out.
Vitamin D exists in two chemically different forms-
· vitamin D2 (ergo-calciferol); present in plants. In PLANTS, the ergo-calciferol (vitamin D2) is derived from UV irradiation of ergosterol (hence, also known as pro-vitamin D2).
· vitamin D3 (chole-calciferol); present in animals. In ANIMALS, chole-calciferol (vitamin D3) is produced in dermis by UV irradiation of 7-dehydro-cholesterol (hence, also called pro-vitamin D3), when skin is exposed to sunlight.
These different forms of Vitamin D regulate some of the most basic and important physiological functions of the body. Mineral absorption (especially calcium) and utilization (bone mineralization), metabolic rate (it has thyroid-related effects), synergies with other nutrients (e.g., vitamin K and vitamin A) and critically modulates a significant amount of gene expression.
There are tests for measuring the levels of all forms of vitamin D.
One of the problems that consumers face is the discrepancy between vitamin D levels recommended by governmental authorities (400 IU) and those needed to get into the normal range (i.e., for a person regularly exposed to the sun during the middle of the day), which can be 3000-8000 IU, depending on skin color. The lighter the skin, the greater the amount of D produced by skin sun exposure. The darker the skin, the less vitamin D produced in the skin. Skin color is not the only modulator of vitamin D. There are differences in dietary absorption efficiency, too.
Another problem is the prevalent recommendations by dermatologists (and other medical professionals) that people avoid the sun for skin-health reasons. This is actually very bad advice. Big-time very. Vitamin D-deficient skin has increased risks of developing most kinds of skin cancers, and the most dangerous kinds of skin cancers. And vitamin D-deficient bodies are at increase risks of developing cancer overall.-skin issue to avoid is sunburn. Regular sun exposure is good for decreasing skin-cancer risks. It is acute sun over-exposure that bad. Be sure to check out my other vitamin D articles.