Vitamin D is absorbed in fat and is thus primarily found in foods of animal origin. Its major role involves bone growth and strength. Indeed, vitamin D is involved in skeletal mineralisation by increasing calcium and phosphorus fixation.
Vitamin D is fat-soluble and heat-resistant and is thus not sensitive to cooking. Vitamin D includes five different molecules (vitamins D1, D2, D3, D4 and D5), which are chemically very similar and have similar biological actions. The most extensively used is vitamin D3, also known as Cholecalciferol. It is characterised in that it is produced by the body in the skin under the effect of sunlight from cholesterol. It is one of the rare vitamins for which dietary intake is secondary compared to endogenous production (by the body on its own) in the case of sufficient exposure to the sun, which is rarely the case in winter. During this season, sufficient vitamin D intake from dietary sources is thus necessary. Vitamin D is stored in the liver, skin, kidneys, spleen, muscles and fat tissue.
Roles
Vitamin D is required for normal growth and normal bone development in children and also for maintaining the skeleton in adults. It supports the uptake and normal utilisation of calcium and phosphorus. Vitamin D helps maintain the muscle and immune functions.
Requirements
Daily vitamin D requirements vary. They are dependent on age, skin pigmentation and sunlight. These requirements increase when pregnant and breastfeeding, during the growth phase and in subjects with dark or sallow skin as they absorb less ultraviolet rays needed by the body to produce vitamin D.
Table of RNI (Reference Nutrient Intakes) for vitamin D :