Essential for bone health and immunity, vitamin D is synthesised by the body under the effect of the sun or provided by food. However, many of us miss them. How to optimize your contributions? When to take vitamin D supplements? In short, here is All About Vitamin D.
- Vitamins D: what is the difference between D2 and D3?
- What is Vitamin D for?
- Where is Vitamin D found?
- Do all skins make the same amount of vitamin D?
- How long should you be in the sun?
- What foods are rich in vitamin D?
- What are our vitamin D needs?
- When to take vitamin D?
- Do vegetarians and vegans need supplements?
When the sun is running out, like in winter, we can more easily run out of Vit D. Some people are particularly at risk for deficiency.
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 exert the same biological activities as they are converted in the body into a substance, commonly known as vitamin D . However, D3 is better assimilated than D2. It has twice the action for an equivalent dose.
By increasing the absorption of calcium and phosphorus and limiting their leakage in the urine, it is essential for the mineralization of bones and teeth: a deficiency of Vit D promotes the risk of rickets in children, osteoporosis and fractures in adults. It also helps to better combat stress, improve nerve transmission and ensure good muscle contraction. Finally, it is a key factor in immunity.
This vitamin has a double origin.
- A part is synthesized by the organism, at the level of the skin, under the action of ultraviolet rays, then stored in the liver, muscles and adipose tissue to be used during winter periods.
- The other part (around 20%) is provided by food, especially by-products of animal and fatty origin.
No. Light skin types (phototypes I to III) make more of it than dark skin types (phototypes IV to VI) which contain more melanin, a pigment which blocks UVB rays.
Age also plays a role: as we age, the synthesis of Vit. D by the skin decreases.
If regular exposure to the sun guarantees, in most people, a good supply of Vit. D, it must of course remain reasonable, to limit the risk of skin cancer . And we obviously protect ourselves with sunscreen
The exposure time depends on many parameters. “In addition to age and phototype, you have to take into account the amount of UVB that reaches the ground. However, this depends on many factors, ”explains experts.
- First the season : there is on average five times more UVB in summer than in winter. Then the time of day: the higher the sun is in the sky, the more there is.
- The Altitude : UV Index increases indeed about 10% every 1000 meters altitude.
- The latitude : when it increases the number of UVB decreases. The presence of clouds and the thickness of the stratospheric ozone layer also play a role.
- Another factor, ground reverberation : grass, earth and water reflect on average 10% of UV radiation, and 15% and fresh snow… 80%!
The foods richest in Vit. D are:
- Cod liver oil: 250 µg of Vit. D per 100 g
- Canned cod liver: 54.3 µg Vit. D per 100 g
- Canned salmon roe: 27 µg Vit. D per 100 g
- Naturally smoked herring: 22 µg of Vit. D per 100 g
- Halibut: 21.2 µg of Vit. D D per 100 g
- Salmon trout: 18.7 µg of Vit. D per 100 g
- Sardine: 14 µg of Vit. D per 100 g
- Margarine: 10 µg of Vit. D per 100 g
- Egg yolk: 2 µg of Vit. D per 100 g
- Cottage cheese at 3%: 1.5 µg of Vit. D per 100 g
They are estimated at 15 µg per day or 200 international units for adults, men and women. These needs are increased in newborns, infants, pregnant women and the elderly, but the precise data are being re-evaluated by the health authorities.
Supplementation is generally recommended for infants , pregnant women and the elderly , as well as for people of color and those suffering from pathologies inducing intestinal malabsorption. This supplementation can be extended to a good part of the population, especially in winter. In all cases, it must be prescribed by the doctor. It can be done at once ( ampoule ) or daily ( drops , capsules …)
- If you are a vegetarian : Vit. D intake can be satisfactory, as long as you consume fish oils, eggs and dairy products.
- If you are vegan: in the absence of animal products, supplementation is essential because the plants contain little Vit. D and do not provide sufficient needs.
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