What is vitamin D and what is it used for? Here's when to take supplements

We know it as a vitamin, but it is actually a pro-hormone. And, contrary to what we might think, its main source is not food but the sun. This is vitamin D, a micronutrient needed in very small amounts but essential for the health of our bodies. It comes to us mostly from the sun because there is very little food with vitamin D, but we can stock up on it thanks to the action of UV-B radiation present precisely in the sun's rays. Its precursor, found in our skin, is first activated by ultraviolet (UV-B, precisely) and then modified in the liver and kidneys to make the active form of vitamin D: cholecalciferol, also known as vitamin D3. But if the human body is able to synthesize it, why is vitamin D deficiency so widespread? How can we notice that our vitamin D3 is low? And how can we prevent or correct it?

The causes of vitamin D deficiency

In many cases, adequate exposure to the sun, combined with that little bit of vitamin D found in foods, could ward off the risk of deficiency. Unfortunately, however, our lifestyles often force us to spend many hours of the day indoors, reducing the amount of UV-B radiation that reaches our skin. What's more, we have to deal with the fact that ultraviolet radiation promotes the development of skin cancers. Therefore, we protect ourselves (or, at least, should protect ourselves) from UV in at least two ways: avoiding exposure during the hours when the sun's rays are most intense and applying appropriate sunscreens to the skin. All this significantly reduces the triggering of vitamin D production in the skin. As if this were not enough, other factors can also reduce the amount of vitamin D3 synthesized by our body:

• our phototype: people with a darker complexion naturally screen UV rays with pigments in their skin;
• the latitude at which we live: the farther toward the poles you go, the less intense the solar radiation;
• the season: in the winter months, when there are fewer hours of daylight and less intense sunlight, the ability to synthesize vitamin D in the skin is reduced.

Finally, circulating vitamin D may also depend on our body composition. Since it is, in fact, a lipophilic molecule, vitamin D tends to accumulate in adipose tissue; the more abundant this is, the more vitamin D can accumulate within it. This, combined with the low availability of vitamin D in foods, can lead to vitamin D deficiency, a problem that can have numerous health consequences. The Consequences of Vitamin D Deficiency At the expense of inadequate vitamin D availability are first and foremost the bones and teeth. Not surprisingly, in the past the most common manifestation of deficiency of this vitamin was rickets, a condition characterized by severe skeletal problems in children. Vitamin D promotes good bone health by promoting theabsorption of calcium and phosphorus. Given this role, other problems associated with its deficiency includeosteoporosis,osteomalacia (a condition due to inadequate mineralization of bones), increased risk of fractures, andsecondary hyperparathyroidism (the increased production of hormones in the parathyroid glands due to low blood calcium levels). Given, however, that vitamin D3's functions and benefits are also others, its deficiency can have other consequences as well. In particular, the vitamin D receptor is also present in the cells of the immune system, those of thesmall intestine, and those of the skin and brain. In addition, this valuable molecule is involved in stimulating the production of insulin (the hormone that regulates the entry of glucose into cells) and in the contraction of heart cells. This is why vitamin D deficiencies can be associated, for example, with alterations in immune defenses.

Symptoms of vitamin D deficiency 

People often realize that they are vitamin D deficient without having noticed the appearance of specific symptoms. There is no shortage, however, of cases in which deficiencies manifest themselves with:

• bone pain
• muscle aches
• muscle weakness

  When to measure vitamin D in the blood and reference values To discover a vitamin D deficiency, a simple blood test is sufficient. According to experts, cases when it is necessary to measure its levels include:

• Rickets, osteomalacia and osteoporosis
• chronic renal failure
• liver failure
• cystic fibrosis
• inflammatory bowel disease
• Crohn's disease
• bariatric surgery
• radiation enteritis
• hyperparathyroidism
• pregnancy and lactation
• Elderly people with a history of falls or nontraumatic fractures
• obesity (even in children)
• Diseases associated with granuloma formation, such as sarcoidosis
• Taking certain medications (antiepileptics, glucocorticoids, antifungals, cholestyramine, medications taken for AIDS)
• some lymphomas

Currently, we speak of vitamin D insufficiency when measured levels are between 20 and 30 ng/ml, while values below 20 ng/ml are referred to as deficiency. There is also no shortage of cases where vitamin D is either very low (below 10 ng/ml) or too high. When it exceeds 150 ng/ml there is a risk of intoxication and problems associated with excess calcium, such as:

• Formation of calcium deposits in soft tissues (for example, in the heart and lungs)
• confusion and disorientation
• kidney damage
• kidney stones
• Nausea, vomiting, constipation, lack of appetite, weakness and weight loss

 When to take vitamin D supplements

As mentioned, there are few food sources of vitamin D. Where is it found? Essentially, in fatty fish, the same fish with which Omega 3 can be taken, for example, mackerel, sardines, sardines, herring, salmon, and tuna. Not surprisingly, cod liver oil supplements (another source rich in these essential fats) can also provide Omega 3 and vitamin D together; compared with the past, products currently on the market provide standardized doses of this micronutrient, added ad hoc after purification of the Omega 3-containing oil. Other foods with vitamin D are fortified foods (i.e., in which vitamin D is added), for example, breakfast cereals or milk. Finally, some mushrooms and chocolate also contain vitamin D; in this case, however, the form present is vitamin D2 (or ergocalciferol) rather than vitamin D3. What does it do? It actually performs the same functions as vitamin D3, but it is not the form synthesized by our bodies.

The best vitamin D supplement varies from case to case. In cases of particularly low blood levels, the doctor may prescribe particularly high doses of vitamin D, sometimes in the form of one-time injections. In all other situations, nonprescription vitamin D supplements may be sufficient. Given the high frequency of vitamin D deficiency, it may happen that the doctor or nutritionist suggests taking supplements even in the absence of blood dosage, especially in the presence of risk factors such as obesity, advanced age, or low outdoor activity.

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