Vitamin D - Benefits and Main Sources

Vitamin D, also known as calciferol, is an essential substance for our health and is responsible for controlling the levels of calcium and phosphorus in the blood and bones. In recent years, vitamin D has gained media attention and medical attention for its alleged actions against infections, cancer and heart disease.

In this article we will review the role of vitamin D in the body, clarifying what are their real benefits and which are only supposition not yet proven by scientific studies. Let's also talk about the risks of your disability in the body.

Foods rich in vitamin D
Foods rich in vitamin D
 


What are vitamins?

Vitamins are substances found in food, being necessary in small quantities for the normal functioning of the body's metabolism. Humans can not produce vitamins (except for vitamin D, as will be explained later) and therefore rely on food to maintain the blood levels necessary for health.

There are 13 essential vitamins, each with a specific action in the body. Vitamins are important for health, but their real role is often overestimated. People tend to think that vitamins are nutrients that act in a generalized way in the body, improving strength, fighting fatigue, preventing infections, opening an appetite, etc. None of this is real. Each vitamin has specific and restricted action. For example, vitamin K is needed for reactions that activate blood clotting; Vitamin B12 is important in the formation of red blood cells; and vitamin A is essential in the formation of tissues lining the eyes.

We need only small amounts of vitamins in the body. Some vitamins when consumed in excess, instead of bringing benefits, lead to poisoning, a condition called hypervitaminosis.

What is vitamin D?

Vitamin D is a substance whose major action is in controlling the levels of calcium in the blood and the health of bones. Calciferol has a particularity in relation to other vitamins: in addition to being acquired through food, it can also be produced by our own body through sun exposure. So while all other vitamins can only be bought in the diet, adequate exposure to sunlight can provide enough vitamin D to our body.

In the next few paragraphs I will explain in more detail the formation and activation of vitamin D in our body. This part although it seems very technical and having complicated nomenclatures will be important later when we talk about the deficiency and the replacement of vitamin D. I will try to be as didactic as possible.

There are two basic forms of vitamin D: cholecalciferol (vitamin D3) and ergocalciferol (vitamin D2). Both can be obtained through food or vitamin supplements. Vitamin D3, however, can also be produced by our body. Through the cholesterol that is consumed in food, we get a substance called 7-dehydrocholesterol. This cholesterol is deposited in skin cells and, when exposed to sunlight (UV-B rays), cholecalciferol (vitamin D3) is transformed.

Both cholecalciferol (vit.D3) and ergocalciferol (vit.D2) are inactive forms of vitamin D. For vitamin D to exert its effects on the body, two more metabolizations are needed.

The process is as follows: vitamins D3 and D2 obtained in the diet and / or sun exposure are transported to the liver, where they will be transformed into calcifediol (25-hydroxyvitamin D). Calcifediol is the form the body uses to store vitamin D. Therefore, when we want to know if the patient has adequate levels of calciferol in the body, we give blood levels of 25-hydroxyvitamin D (25OH vit D).

When the body feels the need to act on blood and bone calcium levels, a part of this 25-hydroxyvitamin D is transported to the kidneys, where it will undergo the last metabolization process, transforming itself into calcitriol (1,25-hydroxyvitamin D), this is the active form of vitamin D.

Therefore, in short, obtaining and activating vitamin D can follow two paths:
  • Food → liver → kidneys
  • Skin → liver → kidneys

Solar exposure

Cholecalciferol (vit.D3) formed after sun exposure is the best and easiest source of vitamin D we can get. The variety of foods rich in vitamin D is small, so frequent sun exposure is necessary for the body to have adequate vitamin D reserves.

Populations living in temperate countries suffer most from a lack of vitamin D. In addition to the lower incidence of sunshine in the winter and fall months, cold weather makes people less likely to leave home, and when they do, need to wear thick, long clothing, preventing skin contact with the sun, even on sunny days. In Europe, about half of the population reaches the end of winter with low levels of calcifediol (25-hydroxyvitamin D), characterizing vitamin D deficiency.

For those who live in countries with high sun exposure, such as Brazil, the risk of deficiency of this vitamin should be very low, but it is not. In fact, the amount of sun a region receives per year is important, but there are other factors that influence the skin's ability to produce cholecalciferol from UV-B rays. Examples:
  • In the Middle East, annual sun exposure is very high, however, this region has high rates of vitamin D deficiency. The main reason is cultural, due to the custom of wearing long clothing, which covers the entire body surface, limiting the skin contact with the sun's rays.
  • Age is another important factor as well. Over the years, the skin is becoming less and less efficient in producing vitamin D, making the elderly a group with a high risk of vitamin D deficiency. In addition to the low efficiency of the skin, the elderly usually have lower consumption of vitamin D in the diet, less exposure to the sun and often spend the day closed at home or in homes for the elderly. In some European countries, more than 80% of the elderly population is deficient in vitamin D. Even in Brazil, it is estimated that half of the elderly population suffers from this deficiency.
  • With the increased awareness of the population regarding the risks of skin cancer due to exaggerated sun exposure, more people are avoiding sunbathing. In addition, frequent use of sunscreen with a high protection factor blocks the UV-B rays, preventing them from being able to stimulate the production of vitamin D in the skin.
  • Skin color is another important factor. Melanin, present in large numbers in people with darker skin, is a pigment that protects us against UV-A and UV-B rays. Melanin is responsible for the lower incidence of skin cancer in black and brown people. However, melanin does not only block the harmful effects of ultraviolet rays. Darker-skinned people need to spend more time in the sun so their skin produces the same amount of cholecalciferol as whiter people. The lack of vitamin D in blacks is very common, especially in those living in countries with low solar incidence.

In general, fair-skinned people need 5 to 10 minutes of sun exposure 2 to 3 times a week. Already darker-skinned people need 30 minutes, three times a week to get the same result. The best time is between 10am and 3pm. The early morning or late afternoon sun is very weak, lacking the ability to stimulate vitamin D production.

Foods rich in vitamin D

Few foods are actually rich in vitamin D, except those whose vitamin is added artificially. In fact, this relative lack of vitamin D in most foods is not a serious problem because our body was "made" to get vitamin D primarily from the sun and not from food. However, people who are not adequately exposed to the sun, whether they live in countries with low sun exposure throughout the year or because they spend the day in institutions, offices or even in the home, end up needing a diet that contains food rich in vitamin D.

Naturally, oily fish are the main sources, especially cod liver oil, canned tuna, salmon and sardines. Other sources of vitamin D include egg yolk, mushrooms and liver steak. Currently, milk derivatives are also rich sources of this vitamin, but only because they are artificially enriched. Therefore, industrialized milk, cheeses and yogurts are also foods that contain vitamin D.

Contrary to popular belief, fruits and vegetables are not sources rich in vitamin D.

As we'll see later, a dose of 600 to 800 IU is needed to maintain vitamin D levels in most adults. As a comparison, look at the amount of vitamin D present in some food samples:
  • Cod liver oil - 1 teaspoon contains 450 IU; 1 tablespoon contains 1350 IU
  • Raw herring - 100 g contains 1628 IU
  • Raw red salmon, canned or cooked - 75 g contains 600 IU
  • Raw pink salmon, canned or cooked - 75 g contains about 500 IU
  • Tuna - 75 g contain about 200 IU
  • Eggs - 2 large units contain about 80 IU
  • Cow steak - 75 g contains about 36 IU

Benefits

The main role of vitamin D is to control the metabolism of calcium and phosphorus, keeping the bones healthy. Children with this vitamin deficiency develop rickets and adults suffer from osteomalacia and osteoporosis. Older people with vitamin D deficiency also have lower muscle strength and a higher risk of falls and fractures of the femoral neck.

In recent years a lot of studies have emerged suggesting other benefits of vitamin D in addition to controlling the metabolism of calcium.

Among the diseases that may be related to the lack of vitamin D we can mention:

It is important to stress that the scientifically proven benefits of vitamin D are only those linked to bone and calcium metabolism. All other alleged actions are not 100% proven. There are preliminary studies, which appear to be real, but which still need to be substantiated by large-scale studies.

Note: There is a large ongoing study on the subject in the US with more than 20,000 patients, which should be finalized by 2016. It is expected that from this study we will have more reliable data on the action of vitamin D in various parts of the body.

Vitamin D deficiency

As vitamin D is stored in the body in the form of calcifediol (25-hydroxyvitamin D), this is the most abundant type of vitamin D in our blood. Therefore, 25-hydroxyvitamin D is the substance we dose when we want to know if the body has adequate amounts of vitamin D.

One of the major difficulties currently in medicine is finding out what the ideal values are for calcifediol (25-hydroxyvitamin D). Over the years, as studies have elucidated the role of vitamin D in the body, the values considered normal have been changing.

Currently, the most accepted values as suitable are between 20 and 40 ng/mL. However, it is possible to find bibliographic sources that say that ideal 25-hydroxyvitamin D values are above 50 ng/mL or up to 75 ng/mL.

Levels greater than 90 ng/mL are often considered to be potentially toxic.

Vitamin D supplements

As experts have not yet reached a consensus on what the proper levels of 25-hydroxyvitamin D are, the criteria for indicating vitamin D supplements remain unclear. There are physicians who indicate supplements when 25-hydroxyvitamin D levels are below 50 ng/mL, while others only when below 30 or 20 ng/mL.

The standards of the American Society of Endocrinology suggest supplementation of vitamin D, aiming to maintain the concentration of 25-hydroxyvitamin D above 30 ng/mL. Usually, the dose of 600 to 800 IU per day is sufficient to reach this target. Supplementation with cholecalciferol (vitamin D3) is more indicated than with ergocalciferol (vit.D2), although the latter is also an acceptable option.

In people with more severe deficiency, such as 25-hydroxyvitamin D levels below 20 or 15 ng / dl, higher daily doses of vitamin D, such as up to 2,000 IU, may be necessary.

If changes in diet and sun exposure are possible, the patient can often achieve adequate 25-hydroxyvitamin D levels without supplementation. It is good to remember that a good dish of salmon even provides 1,000 IU of vitamin D and 30 minutes of sun exposure can produce 10,000 IU of vitamin D.

The elderly, however, are the group that has the most difficulty correcting their vitamin D deficiency without the help of supplements. People who live in colder places also often need vitamin D supplements, especially in the winter.

Since patients with liver or kidney disease are usually unable to adequately metabolize vitamins D2 and D3, replacement is usually done directly with 25-hydroxyvitamin D or 1,25-hydroxyvitamin D.
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