Funtil a few decades ago it was thought that vitamin D only served to ensure strong bones, but it has now been discovered that it has a role, and a non-negligible role, in the functioning of the immune system.

Vitamin D: everything you need to know and false myths
Vitamin D: everything you need to know and false myths

At the same time we also understood how much it was not at all uncommon to incur a deficiency of the substance. In Europe it is estimated that 40 percent of people have vitamin D levels that are too low. Children, adults, elderly.

And here the thought immediately becomes self-referential: perhaps I fall within that level where the vitamin is lacking and if so I risk catching colds, flu and ailments more serious; maybe it’s time to do that long-postponed blood test; better to go directly and buy a supplement. Well, this last option is not ideal.

Locked in the house for too long

A first reason that explains the deficit in Western countries is the life spent within four walls, of home, company or office. There is a reason why D is called the sunshine vitamin: it is synthesized by the skin when exposed to type B ultraviolet rays. Through food, however, you usually assimilate just 10-20 percent of what you need.

Exposing yourself to the sun, albeit with due caution, is the best way to guarantee a good amount of vitamin D (photo Getty Images).

In other words, it is at the same time a micronutrient that can be taken in through food (although not in sufficient quantities) and a hormone that our body produces itself. Without sun, however, no production. With latitude being an objective issue: those who live in the North in the colder seasons are penalized.

Hypovitaminosis after 65

Under the action of UVB rays, the skin produces a precursor of vitamin D, a sort of semi-finished product that is still inactive and which will be transformed by our organism in order to be used in various functions. To be precise, it is the ultraviolets that make the compost evolveor (derived from cholesterol) which sits hidden in the skin in vitamin D3 or cholecalciferol.

Two more chemical steps are needed, in the liver and kidneys, for the actual vitamin D to be introduced into the body’s circuit. The mechanism is perfect until age gets in the way, because over the years we become less good at synthesis: after the age of 65 the body generates only a quarter of the vitamin D it produced at twenty. It’s an average, but it gives a very good idea, so much so that experts recommend administering the supplements to those over 75 without even taking blood tests.

Hypovitaminosis does not just depend on the passage of time. Obesity and marked overweight also have a negative impact, because adipose tissue tends to sequester the substance. The reason is biochemical: the vitamin is fat-soluble, it dissolves in fats, in this case in body fats.

The importance for bones

Once upon a time, D was only talked about in children in whom bone deformations were noted. Cod liver oil was prescribed and then out playing in the yard and on the street. “Air! Air!», was recommended, and the therapy worked: the slimy tasting oil and the sun provided the missing compound. What didn’t fit was the deficiency in adults and the elderly, because it didn’t lead to visible problems.

Today it is known that vitamin D regulates the intestinal absorption of calcium and phosphorus, at the end of digestion, promoting bone mineralization. In this sense it is crucial at every stage of life. First to build the skeleton, then to strengthen it, finally to prevent fractures from osteoporosis, that bone fragility that especially affects after menopause.

Less muscle strength

Filling any gaps in the compound is also useful for other reasons. The substance acts on various levels. One is muscle contractility: low levels of vitamin D cause a decrease in the efficiency of muscle contraction, strength and coordination. And there is the influence on the immune system, on its defense capacity against external and internal enemies.

The possible anti-inflammatory activity is much studied: some research, for example, has shown that vitamin D deficits are related to irritable bowel syndrome or chronic intestinal inflammatory diseases such as Crohn’s.

The relationships with depression, hypertension and atrial fibrillation are also investigated, with metabolic diseases such as diabetes and even with the onset of cancer. Waiting to find out more, theAifa, the Italian Medicines Agency, specifies that «the administration of vitamin D is inappropriate for cardiovascular and tumor prevention». AIFA also underlined that the constantly growing consumption of vitamin D-based medicines (which can only be obtained upon presentation of a medical prescription) is not always justified and therefore placed limits on reimbursement by the National Health Service.

As for over-the-counter supplements, You should be aware that excessive doses of vitamin D can lead to hypercalcemia, a condition in which too much calcium builds up in the blood, leading to the risk of kidney stones. Not only. A recent study reported that the intake of large quantities, paradoxically, can even worsen bone density. The idea that “more is better” applies neither to micronutrients nor to hormones.

The richest foods

Coming to practical advice, spend more outdoors and pay some attention to the table: lVitamin D is found mainly in egg yolk, oily fish, salmon, swordfish and tuna, both fresh and canned. Dairy products also have some of it.

For those who follow a vegan diet, useful information is to know that Vitamin D is found in dried shiitake mushrooms, typical of oriental cuisine but also available here. For everyone, fortified foods are worth taking advantage of. The industry offers a series of products added with vitamin D, from soy drinks to cow’s milk. These are excellent sources, according to a number of studies.

Experimental super tomatoes

A curiosity: a team of Italian researchers from the Cnr and English scientists from the Norwich Institute managed to create a super tomato that could provide the same amount of vitamin D as two eggs or a piece of tuna. The plants were obtained by making changes to a gene with the “cut and sew” technique called Crispr.

The first seeds were planted in Great Britain, now the prospect is to grow tomatoes capable of directly providing active vitamin D. A couple would be enough to cover your daily needs. A natural supplement.

Eliana Liotta (photo by Carlo Furgeri Gilbert).

Eliana Liotta is a journalist, writer and science communicator. On and on the main platforms (Spreaker, Spotify, Apple Podcast and Google Podcast) you can find his podcast series The good that I want.

The review is by Andrea Giustina, director of the Endocrinology Unit at the San Raffaele Hospital in Milan and full professor at the Vita Salute University.