Known for decades for its irreplaceable role in ensuring efficient bone metabolism from birth and throughout life and in preventing osteoporosis and fragility fractures in old age, vitamin D is actually an extremely versatile compound implicated in countless fundamental physiological functions, long unsuspected.
Research conducted over the last twenty years has indicated that maintaining adequate plasma levels of vitamin D is necessary not only to absorb calcium and phosphate and fix them in bones and teeth, but also to reduce the risk of developing diseases affecting various organs and systems and degenerative phenomena related to aging, as well as to ensure the general well-being of the body at any age.
Unfortunately, in the face of clear evidence of usefulness, which should lead anyone to try to constantly supply vitamin D, epidemiological data indicate that in all countries of the world, including Italy, conditions of insufficiency, deficiency and serious deficiency of this fundamental micronutrient are extremely widespread in people of all ages, economic levels and eating and lifestyle habits.
Let’s see in more detail why vitamin D is precious, how to obtain sufficient quantities and thus protect health on many fronts.
Vitamin D: what you need to know
Vitamin D is a fat-soluble compound that tends to accumulate in the adipose tissue of humans and animals and is present in appreciable quantities only in some fatty foods, normally little consumed in the context of the average diet of most people. In nature, vitamin D exists in the form of cholecalciferol (vitamin D3) and ergocalciferol (vitamin D2).
The first derives mainly from the transformation, induced by exposure for a sufficient time to UV B sunlight, of a compound called 7-dehydrocholesterol, contained in the plasma membranes of skin cells.
There are also some good food sources of vitamin D3, represented above all by fatty fish from the North Seas, such as salmon, mackerel and herring, and fish liver oil (in particular, cod, a famous remedy against rickets, widely used in the past because it promotes the skeletal development of children). Smaller amounts of vitamin D3 are provided by beef or pork liver, eggs and cheese.
Vitamin D2 is formed, instead, by the transformation of a compound, called ergosterol, present in the membranes of plant cells, similarly induced by UV B sunlight. Vitamin D2 can therefore be obtained through the consumption of fruits and vegetables, but the amount obtainable from these sources is generally very low, taking into account the average consumption levels. To be quite rich in vitamin D2 are, however, some mushrooms grown in controlled conditions under UV B radiation.
Vitamin | Main food sources |
---|---|
Vitamin D2 | Mushrooms grown under controlled conditions under UV radiation B |
Vitamin D3 | Salmon, mackerel, herring, fish liver oil |
To promote a greater supply of vitamin D through food, enriched foods have long been introduced on the market, in which vitamin D is supplied in dosages compatible with reaching the recommended daily dose and, as a rule, in association with calcium, of which vitamin D mediates intestinal absorption, metabolism and biological activity (not only at bone level).
In the common commercial channels you can find milk, yogurt, cheese, margarines, fruit juices, breakfast cereals and special breads enriched with vitamin D and calcium. However, despite the wide availability of these functional foods and the affordable cost, it is estimated that about half of the population continues to be affected by conditions of vitamin D insufficiency or deficiency or at risk of developing them.
After intestinal absorption, vitamin D is transformed into its biologically active forms, i.e. 25(OH)D and 1,25(OH)D. Blood levels of 25(OH)D are taken as a benchmark to determine whether a person is deficient in vitamin D or is deficient, insufficient or sufficient.
Unfortunately, the diagnosis of vitamin D insufficiency or deficiency cannot be made by evaluating symptoms and clinical signs alone, since the latter begin to manifest only when vitamin D levels are extremely low and have already caused serious damage to the body.
Skin, sun and vitamin D
Daily sun exposure is the simplest, most effective, cheapest and most enjoyable way to fill up on vitamin D. However, to take all the benefits and no damage from UV rays, the sun must be taken in the right way, taking into account some basic principles and respecting appropriate precautions.First of all, it should be noted that, in order for the 7-dehydrocholesterol present in the epidermis to be transformed into vitamin D3, UV B rays must be able to act directly, without being “braked” by clothing or sunscreen (a sunscreen product with a low protection factor, SPF 15, is sufficient to prevent the synthesis of vitamin D3). The skin, therefore, should be presented to the sun totally defenseless. This need clashes, evidently, with the recommendation of dermatologists to always protect the epidermis from UV rays A and B, in order to prevent sunburn, skin aging and other serious problems.
A mediation between the need to synthesize vitamin D3 and protect the skin from certain damage can be obtained by exposing yourself to the sun without sunscreen, but for short periods (about 15 minutes a day) and avoiding the hottest hours of the day (11.00-16.00) and situations of maximum UV radiation B (very clear light, high mountains, open sea, poolside etc.).
With regard to the surface to be exposed, the face, arms and part of the legs offer a sufficient transformation area in spring and summer, when the irradiation is greater, while in autumn-winter, in the geographical areas less close to the equator (including Italy, from North to South), the production of vitamin D3 by this route proves to be insufficient and increasingly scarce as one moves towards Northern Europe.
The benefits of vitamin D
Vitamin D is essential to absorb calcium and phosphate in the intestine and to mediate its use by bone cells.
An inadequate intake of vitamin D, therefore, negatively affects the calcium-phosphorus balance of the body and exposes the risk of developing skeletal malformations in childhood (rickets), of not reaching the peak of bone mass at the end of growth and of undergoing osteopenia conditions as early as 35 years and osteoporosis in old age (especially in postmenopausal women , when estrogen hormone levels drop dramatically and stop protecting the bone).
Vitamin D is also important for dental health. Tooth enamel consists largely of minerals (95-97%) and mainly calcium, potassium, sodium, phosphorus etc. Especially in childhood, an adequate intake of calcium through the diet is crucial for the formation of healthy teeth and protected from the aggression of the bacteria responsible for caries. Also in this case, vitamin D plays a key role and, if it is not present in adequate quantities, both milk teeth and definitive ones can suffer significantly.
Recent research has made it clear that vitamin D is important for oral health for other reasons as well. In particular, it has been observed that vitamin D deficiency is associated, in addition to more fragile teeth and prone to caries, also with a higher incidence of gum disease, such as gingivitis and periodontitis. In this case, the anti-inflammatory, immunostimulating and antibacterial activity of vitamin D would play a decisive protective role.
Muscle metabolism, on which muscle strength and function depend, is also linked to vitamin D and, in particular, to the levels of its active metabolite 1,25(OH)D, which influences protein synthesis. Some evidence indicates that when this metabolite of vitamin D is scarce the muscle is weakened, resulting in lower exercise capacity and efficiency in movement, as well as exposed to a greater risk of mass reduction (sarcopenia).
A growing body of evidence indicates that vitamin D is also important for supporting the proper functioning of the immune system and protecting the body from infectious diseases of a viral or bacterial nature.
Clear evidence of this immunostimulating property has been obtained in the context of the prevention and treatment of infectious diseases of the respiratory system, such as colds, flu and tuberculosis (See also the article “Why vitamin D is useful for the immune system”).
Tuberculosis, in particular, was the first disease for which the therapeutic potential of vitamin D was exploited, albeit unconsciously. Before there were effective antibiotic treatments against the mycobacterium responsible for this serious disease, the patients were sent to mountain places or seaside resorts characterized by pure air and subjected to heliotherapy, consisting of exposure to the sun for a few hours a day, since it had been observed that in this way patients recovered faster. At the time the reason for this favorable outcome was not known: recent studies have clarified that the merit is vitamin D3 produced by the skin stressed by UV rays.
“Ideal” levels of vitamin D
Experts have been discussing for years, without having yet reached a complete agreement, what are the “ideal” plasma levels of 25-(OH)D and the exact daily dose of vitamin D to be taken to maintain them, with a view to obtaining maximum physiological benefits without taking risks.
Currently, the prevailing position identifies a state of deficiency/deficiency for plasma concentrations of 25(OH)D < 20 ng/ml andinsufficiency for values between 21 and 29 ng/ml, while levels >30 ng/ml are considered adequate to protect bone metabolism and benefit from all further favorable actions of vitamin D.
According to the US Institute of Medicine (IOM), however, levels of 25(OH)D ≥ 20 ng / ml can generally be considered adequate, but below 50 ng / ml, a value beyond which adverse effects could begin to occur.
Compared to the amount to be taken daily, the Italian Society of Human Nutrition (SINU) indicates that infants should introduce about 10 μg of vitamin D per day, while children from one year of age, adolescents and adults up to 74 years should take 15 μg / day (including pregnant and breastfeeding women). From the age of 75 onwards, the recommended daily level rises to 20 μg/day.
In all cases, these values correspond to the total intake of vitamin D, i.e. from food and the possible intake of targeted supplements (the dosage of which must be established according to individual needs) for men and women who are in good health.
Joycelyn Elders is the author and creator of EmpowerEssence, a health and wellness blog. Elders is a respected public health advocate and pediatrician dedicated to promoting general health and well-being.
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