Vitamin D: Essential for our immunity
Essential for bone health and immunity, vitamin D is synthesized by the body under the influence of the sun or protein from food. However, many of us do not absorb enough. When the sun is out, as in winter, we may more easily lack vitamin D. Some people are particularly at risk for deficiency.
Vitamins D: what is the difference between D2 and D3?
Vitamin D is a fat-soluble vitamin that exists in two forms: D2, produced by plants, and D3, by animals. In humans, these two forms carry out the same biological activities, since they become the same substance in the body, commonly called vitamin D. However, D3 assimilates better than D2. The one of animal origin has a double action for an equivalent dose from the plants.
What is vitamin D for?
By increasing the absorption of calcium and phosphorus and limiting its leakage into the urine, it is essential for the mineralization of bones and teeth: a deficiency of vitamin D promotes the risk of rickets in children, osteoporosis and fractures in adults. It also helps fight stress, improve nerve transmission, and ensure good muscle contraction. Finally, it is a key factor in immunity.
A part is synthesized by the body, at the level of the skin, under the action of ultraviolet rays, then it is stored in the liver, muscles and adipose tissue to be used during winter periods. The other part (approximately 20%) is provided by food, especially animal and fatty products.
Do all skins produce the same amount of vitamin D?
No. Light skin types (phototypes I to III) produce more than dark skin types (phototypes IV to VI) that contain more melanin, a pigment that blocks UVB rays.
Age also plays a role: As we age, vitamin D synthesis by the skin decreases. Regular sun exposure ensures a good supply of vitamin D for most people, it must of course be reasonable to limit the risk of skin cancer. And obviously we protect with sunscreen.
The exposure time depends on many parameters. "In addition to age and phototype, the amount of UVB reaching the ground must be considered. However, this depends on many factors," explains Jean-François Doré, Director of Research Emeritus. There is an average of five times more UVB in summer than in winter. The higher the sun is in the sky, the more there is. The UV index increases by about 10% every 1000 meters of elevation.
On the other hand, when latitude increases, the amount of UVB decreases. The presence of clouds and the thickness of the stratospheric ozone layer also play an important role. Other factors to consider is the reverberation of the soil: grass, soil and water reflect an average of 10% of UV radiation, 15% of sand and fresh snow a surprising 80%. Without a doubt to ensure correct doses of vitamin D is to consume the correct foods for it. Some of them are: Cod liver oil, pork fat (pork has a high content because it is absorbed in large quantities), sardines, beef liver, pork ribs.
If you are vegan: in the absence of animal products, supplementation is essential because plants contain little vitamin D and do not meet sufficient needs.