Dehydrocholesterol – a provitamin derived from cholesterol – allows humans to synthesize vitamin D3. This molecule, present in the skin through the absorption of the sun’s radiant energy, is transformed into cholecalciferol, which the liver and kidney convert into an active form.
However, the amount of calciferol from food is very limited. In fact, only 10% of one’s needs can be covered by an omnivorous diet. The rest must be obtained from exposure to sunlight or, in its absence, from supplements. The problems associated with the deficiency of this vitamin are exactly the same in omnivores, lacto-ovo-vegetarians and vegans.
The most obvious feature of vitamin D is related to the metabolism of calcium and phosphorus: it maintains the balance of the bone structure (remember that a reduced vitamin D intake leads to reduced absorption of calcium). Today, however, new hypotheses are emerging about the role of this vitamin, which assumes all the characteristics of a hormone: it is considered important both in insulin secretion (in type II diabetes control) and in weight loss, as well as in cardiovascular integrity, in carcinogenesis (linked to cell growth and differentiation), in autoimmune diseases, in the function of muscular and nervous tissue.
That is why it is vital to maintain adequate levels of vitamin D by monitoring not only this but also calcium, phosphorus, parathyroid.
In the development stages, avoiding problems related to rickets, but also in adults and even older people, for related issues such as osteomalacia and osteoporosis. Additionally, it is crucial to maintain the right amount of vitamin D during pregnancy, lactation, weaning, and development of the baby, by evaluating, with the help of a paediatrician, the use of a supplement, which is now generally recommended. As already shown, the source of vitamin D par excellence, from which about 90% of the need is derived, is exposure to sunlight.
Sources from food are extremely limited, and fatty fish such as wild salmon, sardines, mackerel, tuna or cod liver oil- or, in much smaller quantities, whole milk derivatives, eggs and dried mushrooms.
In principle, at our latitudes, it is sufficient to have a solar exposure to the face and upper limbs for 20-30 minutes 2-3 times a week in the summer season. The problem lies in the autumn and winter months, because of the shortage of sunny days and the difficulty of exposure tied to a cold climate This is the reason why vitamin D deficiency is becoming more and more common in the general population (regardless of diet type).
Therefore, it is often necessary to use supplements that, as suggested by Dr Holick, the world's vitamin D guru, preferably in daily doses (1000 to 4000 UI as appropriate) and not weekly or monthly, to achieve optimal blood concentration values of 50-60 ng / ml.
