Vitamin D is a fat-soluble vitamin, which as such can be stored in the body. A small portion of the Vitamin D necessary for the body to function is provided by food, but the greater part is produced directly by the body with the aid of sunlight.
Principal natural sources of Vitamin D
Animal sources: Vitamin D3 (cholecalficerol) is found in fish oils (halibut and cod), egg yolks, animal livers, oily fish (including mackerel, salmon and sardines), enriched milk (whole milk and soya milk), butter and some types of cheese.
Plant sources: Vitamin D2 (ergocalciferol) is found in mushrooms, yeast, cereals, raw green vegetables and vegetable oils.
Vitamin D2 can also be obtained by synthesis. Vitamin D3 is the most bioavailable form.
Properties of Vitamin D
Its principal role is in the growth and strength of bones. In fact, Vitamin D plays a part in mineralisation of the skeleton by helping calcium and phosphorus to bind to it.
Vitamin D is also involved in maintenance of muscle function and immunity.
Recommended Daily Intake
This is fixed at 5 mcg daily (200 UI), but scientists are all agreed on the health benefits of higher doses (up to 4 times higher), especially for vulnerable populations such as teenagers or elderly people.
80% of the French population is Vitamin-D deficient.
Daily Vitamin D requirements vary. They depend on age, skin pigmentation levels and exposure to sunshine.
These needs increase during pregnancy and breast feeding, as well as during growth and in people with dark or olive skin as they absorb less of the ultraviolet that the body needs to manufacture the Vitamin D.
To satisfy Vitamin D requirements, exposure to sunshine for at least 15 minutes per day (face, arms and legs) is necessary. This is why people who live in areas with limited sunshine hours or are not exposed to sunshine are often lacking in Vitamin D.
Over the age of 60 years, Vitamin D supplementation will reduce the risk of loss of bone minerals.