What is Vitamin D and what is it for?

Where it is found, what are the beneficial effects and what its deficiency entails

by Lorenzo Ciotti
What is Vitamin D and what is it for?
© Matt Cardy / Stringer Getty Images News

As I explained in a previous article, there are few foods that contain appreciable quantities of vitamin D. A particularly rich food is cod liver oil. Followed by fatty fish such as salmon and herring, egg, liver, red meat and green vegetables.

In case of vitamin D deficiency, the first alterations consist of: decrease in serum calcium and phosphorus levels with consequent secondary hyperparathyroidism and increase in the concentration of alkaline phosphatase. There is an alteration of the mineralization processes with rickets in children not exposed to the sun and osteomalacia in adults not exposed to the sun, muscle weakness, bone deformation in case of bone disease and pain.

Some studies from 2006 brought to light how vitamin D deficiency may be linked to flu syndrome: according to the team of researchers, the reason could be associated with the fact that this vitamin stimulates the production of antimicrobials in the lungs.

Other studies from 2009 correlate vitamin deficiency, especially in the neonatal phase, with the onset of multiple sclerosis.

But what is Vitamin D and what is it for?

Vitamin D is a group of fat-soluble prohormones made up of 5 different vitamins: vitamin D1, D2, D3, D4 and D5.

The two most important forms in which vitamin D can be found are vitamin D2 and vitamin D3, both with very similar biological activity. Ergocalciferol comes from plants, while cholecalciferol, derived from cholesterol, is synthesized in animal organisms.

The main source of vitamin D for the human body is exposure to solar radiation. Vitamin D obtained from sun exposure or through diet is present in a biologically inactive form and must undergo two hydroxylation reactions to be transformed into calcitriol, the biologically active form.

Vitamin D promotes the reabsorption of calcium at the renal level, the intestinal absorption of phosphorus and calcium, the processes of bone mineralization and also of differentiation of some cell lines and in some neuromuscular functions, although these last two points have yet to be clarified.

Vitamin D supplements have been widely marketed for their claimed anticancer properties. An association between low vitamin D levels and the risk of certain cancers has been noted in some observational studies. Some studies suggest that vitamin D may play a role in regulating the innate immune response against microbial agents.

Low levels of vitamin D appear to be associated with depressive phenomena: a 2013 review study published in the British Journal of Psychiatry analyzed more than 30,000 individuals, finding a consistent correlation between vitamin D deficiency and a higher rate of depression, a correlation that , according to the study, should be confirmed with further research.