The term “vitamin D” refers to both ergocalciferol (Vitamin D2) and cholecalciferol (vitamin D3). Due to exposure to sunlight, ergocalciferol is formed from ergosterol in yeasts and plants, while cholecalciferol is synthesized from 7-dehydrocholesterol (7-DHC) humans and animals. The metabolically active form in the body from vitamin D2 and vitamin D derives 1,25-dihydroxy vitamin D or calcitriol. For what has just been said, vitamin D is a micronutrient with very peculiar characteristics: in fact, the coverage of its metabolic needs can be independent of the diet.
In fact, in temperate latitudes, and for normal sun exposure, on average, 80% of the vitamin D made available to the body comes from its skin synthesis and only 20% from food. The history of vitamin D began in 1919 when Huldschinsky pointed out that children with rickets recovered when exposed to sunlight; later, a similar result was obtained by Hess and Gutman with sunlight.
In the same period, Mc Collum hypothesized a fat-soluble compound essential for bone metabolism in fish liver oil.
Vitamin D has a dual function, endocrine and paracrine. The first function of vitamin D is to regulate the metabolism of Ca and P and control their blood concentrations. In the intestine, markedly increases the absorption of Ca and P in the brush border. In the bone tissue, it favors the differentiation of monocytes into osteoclasts and consequently increases the reabsorption of bone mineral and the release of Ca. The direct effect on renal reabsorption of Ca and P is less certain.
Vitamin D is also important for the correct tropism of the muscular system; it stimulates the synthesis of muscle proteins and participates in the activation of some Ca transport mechanisms in the sarcoplasmic reticulum, essential for muscle contraction.
Evidence from the literature also suggests significant relationships of serum vitamin D concentrations with appendicular muscle strength and overall level of physical efficiency. This localized synthesis does not contribute to calcium homeostasis but appears to be involved in cellular functions’ paracrine regulation. In particular, the vitamin regulates the biosynthesis and release of insulin by pancreatic islet cells and significantly influences peripheral tissues’ sensitivity to insulin itself.
How to get vitamin D?
It also regulates the transcription of the renin gene by acting on the transcription factor and CREB. The anti-inflammatory properties of vitamin D also appear to perform an effective protective action on the vessel wall.
Finally, the vitamin D-VDR system regulates the gene expression of natriuretic peptides, which are not simply markers of cardiac hypertrophy but also autocrine-paracrine factors capable of regulating cardiac development mass in response to physiological and pathological stimuli.
Vitamin D also has potential anticarcinogenic effects due to mechanisms such as:
- stimulation of the immune response;
- enzymatic inhibition;
- modulation of growth factors;
- promotion of pro-apoptosis mechanisms;
- inhibition of carcinogenesis mechanisms;
- inhibition of angiogenesis;
- reduction of local invasion and tumor metastasis;
- induction of autophagy;
- increased antioxidant and DNA repair activity.
As far as the immune response is concerned, vitamin D’s action has been associated with an increase in innate immunity against different infections, particularly tuberculosis, influenza, and viral infections of the upper respiratory.
Why do you need vitamin D
Vitamin D ensures the absorption of calcium and phosphorus by the body from food; lack of this vitamin is the main cause of rickets in children.
In adults, a lack of vitamin D over time increases the likelihood of developing osteoporosis (this is a disease of the skeleton, a decrease in bone density); besides, recent studies have linked vitamin D deficiency to a weakened immune system and the risk of cardiovascular disease.
When vitamin D deficiency can occur
The human body can make its own vitamin D, but this requires sunlight to hit the skin. The amount of vitamin produced depends on the season, length of daylight hours, cloud cover, closed clothing, and whether or not you use sunscreen.
Vitamin D is fat-soluble and can be stored in adipose tissue. If you have eaten many vitamin D-rich foods during the summer and have been in the sun a lot, this may be enough for the winter. The ultraviolet light necessary for the production of vitamin D does not penetrate the glass.
How to get vitamin D in isolation
If you isolate yourself in a country house, sometimes go out into the sun. It is synthesized in the skin by the action of UVB rays; for this, you need to spend at least 5 minutes a day in the sun and in open clothes. Some contradiction arises here in health care: it is known that prolonged exposure to the sun, especially without sunscreen, is dangerous for the skin. If you do not have your own yard or garden, or are afraid of direct sunlight, look at other sources.
Should you take a vitamin supplement? It is better to get tested for Protine when the opportunity arises. Overdose is possible and can be dangerous. The daily dose for children and adults is 15 mcg (600 IU) per day; the maximum dose is 100 μg (4000 IU). Carefully study the package’s information and pay attention to your diet (you may already receive part of the required amount with food).
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Vitamin D-rich foods
Compared to the intuitive intake of vitamin D, “just in case,” getting it from food is a safer way: the concentrations in foods are relatively low, which means there is less risk of overdose.
– Fatty fish: salmon, herring, tuna, mackerel, eel, sardines, and caviar. 400 IU of vitamin D is found in 150 g of salmon or 850 g of cod. The record-breaking product is cod liver oil: 250 mcg per 100 g of product (this is a lot: the daily allowance for an adult is 15 mcg).
– Fatty dairy products: butter, cheese. In 1923, American biochemist Harry Stenbock patented a way to increase vitamin D in foods through ultraviolet irradiation. Dairy products fortified with vitamin D can be found today, but not so often.
– Egg yolks (eggs can be chicken or quail).
– Forest mushrooms: chanterelles, porcini, honey agarics.
Nutritional values: where to find vitamin D
- The food with the highest concentration of D is cod liver oil (210μg / 100g). Foods high in D are fish. In particular, the fatty ones such as herring (30μg / 100g), fresh tuna (16μg / 100g), and canned salmon (17μg / 100g). They are a good source also anchovies (11μg / 100g), the trout (10μg / 100g), and mackerel (3μg / 100g).
- Chicken eggs have a D content of 1.7μg / 100g. But we find it exclusively in the yolk .
- The only one to have it in appreciable quantities is pork liver (1.7μg / 100g) among the meats.
- For some years, we have also found fortified foods (vegetable drinks enriched in calcium and D) in order to prevent the deficit in the population.
Therefore, it is classified as a calcium hormone due to its physiological function of allowing the intestinal absorption of calcium and phosphate. It is essential for the performance of some vital biological functions. Let’s see which ones:
- Strong and healthy bones. D is instrumental in keeping the skeletal system healthy by helping to prevent osteoporosis and fractures. This happens because vitamin D stimulates the absorption of calcium and phosphorus, as well as favoring their deposit.
- Psoriasis, atopic dermatitis, and vitiligo. This vitamin is also a valuable aid for the treatment and prevention of these skin diseases.
- Depression. Synthesized thanks to sunlight, vitamin D stimulates the production of endorphins, serotonin, and dopamine. That is all those hormones that cause a feeling of extreme well-being in our body.
- Insulin. This vitamin has the property of improving the functionality of insulin, a hormone necessary to metabolize sugars, revealing itself to help in the treatment of diabetes.
- The stimulus of hunger. It proves to be of great help in managing compulsive hunger attacks. It also promotes leptin production, which serves to attenuate the stimulus of hunger, causing an adequate sense of satiety.
- Muscles. It also improves muscle tone. In fact, it is able to stimulate the production of muscle proteins, and promote the transport of calcium, essential in muscle contraction.
- C Ravello. It is also very important for the brain. In fact, it helps prevent neurovegetative diseases such as Alzheimer’s or Parkinson’s by protecting cognitive functions.
- Immune system. It stimulates the immune system, thus reducing the number of inflammation and, consequently, infections.
- Vitamin D and tumors. Recent studies claim that D is also useful in preventing some cancers and some autoimmune diseases.
- Cardiovascular pathologies. It would seem able to decrease high blood pressure, consequently reducing the risk of cardiovascular diseases.
10 FOODS WITH THE MOST VITAMIN D
In raw form, such mushrooms are rarely found on our counters, but dry – easily. It is believed that dried shiitake is even healthier. The content of vitamin D in them – 0.163 mg in 50 grams, increases immunity, and improves the state of the cardiovascular system.
During the New Year holidays, probably, everyone had a good supply of vitamin D thanks to caviar. One tablespoon of this delicacy contains 0.020 mg of the vitamin. In addition, caviar is not only rich in omega-3s, but it can also fight depression and other diseases. But, of course, only a high-quality product has all these properties.
The simplest and cheapest source of vitamin D compared to caviar is eggs. We often eat them for breakfast and add them to salads and soups, but someone may not know that eggs contain many”solar” vitamins. Its high concentration is found precisely in the yolk – 0.042 mg in one.
You can also consume beef liver to diversify your diet and increase your vitamin D levels. Although there is not much of this vitamin in it – 0.053 mg in a ready-made serving (100 grams), there is also vitamin A, iron, and protein. Livers need to be as careful as eggs and consumed in small amounts due to cholesterol.
Soy milk is loved by both vegetarians and supporters of a healthy lifestyle. And it’s not just that: fortified milk has a high content of vitamin D (0.127 mg in one cup) and iron. But still, the amount of these vitamins and elements can fluctuate depending on the manufacturer since everyone enriches milk with vitamins at his discretion. The same goes for regular milk.
THE MOST VITAMIN D FOODS
Both fresh tuna and canned tuna will be equally useful: both there and there are important vitamins and minerals, including vitamin D – one serving (about 100 grams) contains half the daily value. Tuna is one of the main sources of lean protein and omega-3s, as well as iron. If you decide to buy canned tuna, then carefully read the composition and give preference to preservation in your own juice.
As with other types of fish, sardines are high in omega-3 fatty acid, which plays a huge role in our body’s functioning – from the formation of cell membranes to the formation of energy. Sardines contain calcium, potassium, iron, and other vitamins and elements. It is abundant in these small fish – in 100 grams, it contains 0.508 mg.
Salmon is also rich in vitamin D – one serving (about 100 grams) contains 75% of the daily value and, of course, omega-3. But including this redfish in your diet is not only necessary for these reasons: it promotes good brain function, reduces the risk of Alzheimer’s disease and other degenerative brain diseases.
If all of the above types of fish are not to your liking, then you can eat herring to increase your vitamin D levels. Despite the lower price (in comparison with fresh tuna and salmon). Herring is not inferior in terms of the amount of “sunny” vitamin in its composition. From 100 grams of fresh or canned fish, you can easily get half the daily value.
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