Vitamin D. Tolerable Upper Intake Levels for Vitamin D

What is, how and where is it synthesized, what vital functions it is responsible for in our body and where it can be obtained from.

Having been born and having lived almost all my childhood and youth beyond the Arctic Circle, I know firsthand what it means not to see the sun. Easy 6 months a year. And still very often get sick, always for some reason, just at a time when there is no sun.

Now I already understand that we did not have the opportunity to receive V itamine D from the sun and eat foods rich in it. And even vitamin complexes did not give the necessary concentration of Vitamin D in the blood, since they contained Vitamin D2, which is very difficult for our body to absorb.

More and more attention is being drawn to this seemingly simple vitamin, which our body can synthesize itself under the influence of sunlight. Recent studies assure that Vitamin D is extremely important for our body and its deficiency can lead to the development of a wide variety of diseases, ranging from simple colds to cancer.

What is Vitamin D

Vitamin D is a group of fat-soluble vitamins, which are steroid hormones in structure.

There are 2 forms:

• Vitamin D2 or Calciferol (Calciferol)- poorly digestible form.

• Vitamin D3 or Cholecalciferol- a natural form, synthesized upon contact of the skin with the sun's rays. Vitamin D3 has a stronger effect than Vitamin D2. It also turns into an active form 500 times faster than Vitamin D2.

The mechanism of formation of Vitamin D

When Sun rays UVB spectrum reaches our skin, special molecules called 7-Dehydrocholesterol(which are synthesized, among other things, from Cholesterol) are converted to Vitamin D3.

The process of absorption of Vitamin D3 into the blood after the rays hit the skin can take up to 48 hours. Therefore, it is very important not to use soap after sunbathing, taking a shower or bath.

It's also important to understand that overuse of sunscreen can do more harm than good (blocking Vitamin D synthesis and harmful chemicals in these products). You can read about this .

Calcitriol is then transported from the liver, again through the bloodstream, to the kidney cells, where it is converted into the most active form of Vitamin D - 1.25 Dihydroxycholecalciferol which is used by our body for numerous, important functions.

What is Vitamin D for?

• affects almost 3 thousand out of 24 thousand of our genes

• controls the level of minerals in the blood and maintains the health of the musculoskeletal system

• regulates the body's ability to resist infections and chronic inflammation

• helps normalize cholesterol levels

• studies prove that by normalizing the level of Vitamin D in the blood, you canreduce the possibility of developing cancer by up to 70%(I wrote about the relationship between vitamin D deficiency and cancer )

• significantly reduces the possibility of complications during pregnancy and childbirth

• prevents the occurrence of melanoma (skin cancer)

• a low level of Vitamin D puts you at risk of developing: Parkinson's disease, diabetes, diseases of the cardiovascular system, hypertension, stroke, Alzheimer's disease, and cancer

Vitamin D deficiency

According to recent reports, more than 70% of people do not get enough of this important vitamin.

Here are some reasons:

• insufficient or inappropriate time spent in the sun to synthesize Vitamin D

• insufficient intake of foods rich in Vitamin D

• overuse of sunscreen

• You are 50 years old or older

• you are overweight

• you have gastrointestinal problems that may interfere with the absorption of fat

How to get Vitamin D

• The best (and free) thing you can do is sunbathe. UVB rays required for synthesis Vitamin D most active in summer, at noon. 10-15 minutes will be enough. You can read in more detail .

• Getting enough Vitamin D from food is problematic. Foods containing the most: cod liver, oily fish, caviar, milk and dairy products, eggs and mushrooms.

• When taking vitamin supplements, be sure to choose the most active natural form - Vitamin D3 (as Cholecalciferol)... Vitamin K2 is also vital for the absorption of Vitamin D. Therefore, they must be taken in pairs. I personally accept this one

Vitamin D has occupied a place among the substances vital for humans discovered and studied by science for about a hundred years. Everyone has probably heard about the benefits of the sun vitamin, but what exactly is it useful for? This article will tell you about what vitamin D is, where it is contained, and why its deficiency and excess are dangerous.

Often all D vitamins are collectively referred to as calciferol, despite the fact that this is the name of a particular vitamin - D3. V medical practice vitamin D refers to the D2 and D3 forms; they are considered the most active and therefore most effective in providing the required action. The functions of all these vitamins are similar, so we can say that they differ mainly in activity and method of production. In published articles, they are most often not separated, even doctors, when talking about vitamin D, mean all of its forms. If we are talking about a specific vitamin, it is mentioned separately.

According to modern science, vitamin D comes in six forms:

• D1- a form containing two steroid derivatives, ergocalciferol and lumisterol. It was first found over a hundred years ago in cod liver. V pure form the vitamin is not found and can only be obtained through chemical synthesis. D1 contributes to the normal growth of bone tissue, controls the level of macronutrients in the body. With sufficient intake, it can be stored in muscle and adipose tissues and consumed as needed.
• D2, or ergocalciferol, is formed by exposure ultraviolet rays on ergosterol. In nature, it is synthesized by fungi. D2 can be called both a vitamin and a hormone at the same time - it regulates the level of calcium and phosphorus and at the same time affects the work internal organs using your own receptors. If the body needs calcium or phosphorus, it begins to actively synthesize this vitamin or use up its reserves.
• D3, or, in other words, cholecalciferol is the most important vitamin in its group. It participates in a huge number of processes at the organismic level, affects most systems - nervous, circulatory, immune.
• D4- dihydroergocalciferol - is responsible, like other D vitamins, for maintaining metabolism and controlling macronutrients. But, unlike the others, it has a special function - it is responsible for the production of a special hormone by the thyroid gland, which removes calcium from the body's bone reserves into the blood.
• D5, or sitocalciferol, in its structure and properties is very similar to vitamin D3, but much less toxic. Due to this, the vitamin is successfully used in medicine - for example, in anti-inflammatory therapy and in the treatment of diabetes.
• D6, otherwise stigmacalciferol is considered a low potency vitamin. Responsible for the prevention of osteoporosis and rickets, ensures the normal development of the skeletal system.

Indications for use

Group D vitamins are prescribed for therapeutic and prophylactic purposes. In the first case, the vitamin is taken in combination with the main therapy, most often for diseases with pathologies of the skeletal system and a lack of calcium in the blood. The difference between medicinal and preventive measures only in dosage: during treatment, drugs are taken in a daily amount of 100-250 mcg, with prophylaxis - 10-15 mcg.

• Treatment and prevention of rickets
• Fractures and poor healing
• Osteoporosis
• Hypothyroidism
• Liver disease
• Increased fragility of bones
• Chronic gastritis, pancreatitis
• Low levels of vitamin D in the body
• Dental tissue disorders
• Tuberculosis
• Diathesis

Contraindications

Despite all the benefits of vitamin D, there are a number of diseases in which its use is contraindicated:

• Hypercalcemia (excess calcium in the blood)
• Stomach and duodenal ulcers
• Active form of pulmonary tuberculosis
• Vitamin D hypervitaminosis
• Acute renal failure
• Heart defects
• Ischemic disease
• Chronic kidney disease

Vitamin D should be taken with caution when:

• Atherosclerosis
• Heart and kidney failure
• During pregnancy and lactation

Dosage

Even for healthy person the dosage of vitamin D is not the same. It all depends on age, weight, and the presence of other factors. Normally, the dosage of the vitamin is approximately as follows:

• For infants under 1 year old - 7-10 mcg (280-400 IU)
• For children from 1 to 5 years old - 10-12 mcg (400-480 IU)
• For children from 5 to 13 years old - 2-3 mcg (80-120 IU)
• For men and women over 13 years old - 2-5 mcg (80-200 IU)
• For the elderly after 60 - 12-15 mcg (480-600 IU)
• For breastfeeding women - 10 mcg (400 IU)

To indicate the dosage of vitamin D, micrograms (mcg) and international units (IU) are used. These units of measurement are interchangeable. One international unit equals 0.025 μg and one microgram equals 40 IU.

The dosages shown in the list are optimal to safely replenish vitamin stores. The maximum permissible daily dose for an adult is considered to be 15 mcg. Exceeding it can provoke hypervitaminosis and, as a result, the manifestation of unpleasant symptoms.

What is contained?

Vitamin D is often referred to as the sunshine vitamin, and for good reason. Almost all of its forms, except for D2, are synthesized in the epidermis of the skin under the influence of ultraviolet radiation. Pro-vitamin D3 is converted into cholecalciferol (directly D3) due to thermal isomerization, after which it enters the bloodstream and is transferred by it to the liver.

In summer, the vitamin is sufficient for the body to function normally, but in winter its production is significantly reduced. A large amount of clothing and short daylight hours prevent it from synthesizing in normal quantities.

In addition to synthesis in the human body, vitamin D is found in food, and for the most part in animal products. So, there is a lot of it in any meat, fish, meat and fish liver, eggs. A high vitamin content is also noted in fermented milk products.

There is practically no vitamin D in plant foods. It is found in small amounts in corn oil, potatoes, and parsley.

Deficit and oversupply

Deficit vitamin D is noted in every tenth inhabitant of our planet. A person suffering from hypovitaminosis quickly gets tired, he develops weakness, muscle pain, problems with teeth, vision. If you do not pay attention to these symptoms in time, the patient may face more serious diseases - rickets, osteoporosis, arthritis, bone deformities.

Rahita mostly young children are affected. With a lack of vitamin D, they may experience hair loss, sweating, and teething problems. In severe cases, the bones of the chest can be deformed and softened, a hump appears. Therefore, it is important for pregnant women to ensure that the level of the vitamin remains normal, and infants are allowed to give it from the first months of life.

Osteoporosis - another disease associated with hypovitaminosis. It is most common among middle-aged and older people and leads to the fact that any, even a slight injury, leads to cracks or bone fractures. To date, it is impossible to completely cure it, only take additional vitamin D and pain relievers.

Depression and migraine are often included in this list of diseases, explaining their development by vitamin deficiency.

Overdose, although it is less common, it still has a place to be. Vitamin D tends to accumulate in the body, and its excess can provoke convulsions, disturbed heartbeat and breathing, weakness, nausea, high blood pressure. Sometimes atherosclerotic plaques associated with excess calcium levels form on the walls of blood vessels.

Hypervitaminosis can occur only in the case of taking large doses of preparations containing vitamin D. Long exposure to the sun does not threaten an excess - from this, the human skin is protected by sunburn.

Treatment consists of vitamin cessation and a plant-based diet. Sun exposure will also have to be avoided. In some cases, it is required to take medications that remove calcium from the body, or even hospital observation.

A blood test can be used to detect a lack or excess of vitamin D. For greater reliability, for several days before donating blood, it is recommended to stop taking vitamin complexes and preparations that may contain it.

Side effect

Vitamin D has many side effects. They can manifest themselves in two situations - in case of misuse or due to individual intolerance. These effects include low blood pressure, weakness, irritability, and nausea. If the daily intake of the vitamin is systematically exceeded, calcifications may form in the organs.

Preparations containing vitamin D

Aquadetrim

The most famous and safe drug that is suitable not only for adults, but also for young children. One drop contains about 600 IU of the vitamin, which is an approximate daily requirement. The drug is prescribed for the prevention of rickets, it can be taken regardless of the time of eating. Recommended to dilute in a spoonful of water.

Alpha D3-Teva

The drug is available in the form of capsules with an oil solution. Approved for use by children over 6 years old and adults - young children cannot swallow the capsule whole. Contains a synthetic analogue of vitamin D, is prescribed for patients with endocrine system disorders. Take one or two capsules after meals with clean water.

Vitamin D3

It is an oil solution and is taken similarly to Aquadetrim. It can be used as an injection, an injection is given intramuscularly in the thigh or buttocks.

Calcium D3-Nycomed Forte

Available in citrus or mint flavored tablets. One tablet contains the daily requirement of vitamin D3 and calcium. It is taken after or with a meal and is intended for children over six years of age and adults.

Vigantol

The drug is produced in the form oil solution... Suitable for children from birth and adults, it is prescribed for the prevention of rickets, the treatment of osteoporosis.

Chemical structure and properties . In 1936, A. Vindaus isolated a drug that cured rickets from fish oil. It was named vitamin D 3, since earlier by A. Hess and M. Weinstock ergosterol was isolated from vegetable oils, called vitamin D 1, When exposed to vitamin D 1 by UV rays, a compound that cures rickets was formed - vitamin D 2, ergocalciferol ( calciferol means calcium carrier). In plants under UV irradiation, other vitamers of ergosterol are synthesized (D 4 - 7). The most important vitamin D group is vitamin D 3 - cholecalciferol. Cholecalciferol is formed as an intermediate in the biosynthesis of cholesterol (from 7-dehydrocholesterol) in human skin cells under the influence of UV rays.

The daily requirement of vitamin D. Food sources of vitamin D. Vitamin D 3 is found exclusively in animal food. Fish oil is especially rich in it. It is contained in the liver, yolk of eggs. Vitamin D 2 is present in vegetable oils and milk. There is a lot of it in yeast. It is biologically less active. The daily requirement for children ranges from 10 to 25 mcg (500-1000 IU), in adults it is less.

Vitamin D metabolism. Group D vitamins are absorbed like vitamin A. In the liver, vitamins are hydroxylated by the microsomal system of oxygenases at C-25 (25 (OH) -D 3 is formed from vitamin D 3, i.e. 25-hydroxycholecalciferol), and then carried by current blood by means of a specific transport protein to the kidneys. In the kidneys, the second reaction of hydroxylation at C-1 is carried out with the help of mitochondrial oxygenases (1.25 (OH) 2-D 3 is formed, i.e., 1.25-dihydroxycholecalciferol, or calcitriol). This reaction is activated by parathyroid hormone secreted by parathyroid when the level of calcium in the blood decreases. If the calcium level is adequate to the physiological needs of the body, secondary hydroxylation occurs at C-24 (instead of C-1), and an inactive metabolite 1,24 (OH) 2-D 3 is formed. Vitamin C is involved in hydroxylation reactions.

Vitamin D 3 is stored in adipose tissue. It is excreted mainly in the feces in unchanged or oxidized form, as well as in the form of conjugates.

Biochemical functions of vitamin D. Vitamin D 3 can be considered as a pro-hormone, since it is converted into 1.25 (OH) 2-D 3, which acts similarly to steroid hormones. So, penetrating into target cells, it binds to protein receptors that migrate into the cell nucleus. In enterocytes, this hormone-receptor complex stimulates the transcription of mRNA, which carries information for the synthesis of a calcium ion carrier protein. Probably, the vitamin is also responsible for the synthesis of Ca2 + -ATPase in different cells. In the intestine, calcium absorption is carried out both by facilitated diffusion (with the participation of a calcium-binding protein) and by active transport (with the help of Ca2 + -ATPase). At the same time, the absorption of phosphorus is accelerated.
V bone tissue 1,25 (OH) 2-D 3 stimulates the process of demineralization (synergistically with parathyrin). In the kidneys, activation by vitamin 1.25 (OH) 2-D 3 calcium ATPase of the renal tubular membranes leads to an increase in the reabsorption of calcium ions; the reabsorption of phosphates also increases. Calcitriol is involved in the regulation of growth and differentiation of bone marrow cells. It has antioxidant and anticarcinogenic properties.

Vitamin D hypovitaminosis. Lack of vitamin D in children leads to rickets. The main manifestations of this disease are reduced to the symptoms of calcium deficiency. First of all, osteogenesis suffers: there is a deformation of the skeleton of the limbs (their curvature as a result of softening - osteomalacia), skull (late fusion of fontanelles), chest (the appearance of a kind of "rosary" on the bone-cartilaginous border of the ribs), teething is delayed. Muscle hypotension (enlarged abdomen) develops, neuromuscular excitability increases (in the infant, a symptom of baldness of the back of the head is revealed due to frequent rotation of the head), seizures may occur. In an adult, calcium deficiency in the body leads to caries and osteomalacia; in the elderly - to the development of osteoporosis (a decrease in bone density due to impaired osteosynthesis). The destruction of the inorganic matrix is ​​explained by the increased "leaching" of calcium from the bone tissue and impaired reabsorption of calcium in the renal tubules with vitamin D deficiency. in response to hypocalcemia, parathyrin is secreted and the flow of calcium from the bone into the bloodstream increases (solid arrow) (secondary hyperparathyroidism).

Hypervitaminosis D. Excessive intake of vitamin D leads to intoxication and is accompanied by pronounced demineralization of bones - up to their fractures. The calcium content in the blood rises. This leads to calcification of soft tissues, kidneys are especially prone to this process (stones form and renal failure develops).

The increase in the level of calcium (and phosphorus) in the blood is explained as follows: 1) bone resorption (solid arrow); 2) an increase in the intensity of absorption of calcium and phosphorus in the intestine and 3) an increase in their absorption in the kidneys (i.e., inhibition of urinary excretion - dotted line).

Under normal conditions, an increase in blood calcium will lead to the formation of inactive 24.25 (OH) 2-D 3, which does not cause bone resorption ("resorption"), however, with hypervitaminosis D, this mechanism becomes ineffective. Interestingly, skin pigmentation (sunburn) is a protective factor that protects against excessive formation of vitamin D when the skin is exposed to UV radiation. However, the light-skinned inhabitants of the northern countries, lacking solar insolation, do not develop vitamin D-deficiency states, as a rule, since their diet includes fish oil.

Assessment of the body's supply of vitamin D. The body's supply of vitamin D is assessed based on the determination active forms vitamin D in blood and tissues by radio competitive analysis; the content of calcium, phosphorus and activity of alkaline phosphatase in the blood serum; the level of urinary phosphate excretion. Stress tests are also used with the intake of fixed doses of calcium for parenteral administration, followed by the determination of the calcium content in the blood and its excretion in the urine.

Vitamin D has been one of the most popular and widely discussed vitamins in recent decades. Since vitamin D was first recommended as a key nutrient in 1943, it has a long history of research.

Initially, daily requirement vitamin D contained approximately 200 IU (5 μg cholecalciferol). Over the years, this level has gradually increased. First, up to 400 IU (10 μg cholecalciferol), and then up to 400-800 IU (10-20 μg cholecalciferol). However, the latest recommended daily intake remains controversial for three reasons.

First, it is a well-known fact that human skin cells can synthesize vitamin D in the sun. Under the influence ultraviolet radiation B (UVB) our skin cells (keratinocytes) convert 7-dehydrocholesterol into a form of provitamin D called cholecalciferol. The amount of pigments in skin cells, the strength of UV radiation, the use of sunscreens, the general health of our skin and other factors affect the production of the vitamin. Therefore, it is difficult to accurately predict the amount of vitamin D produced.

Second, cholecalciferol is not the same as active vitamin D. For its formation, cholecalciferol must be transported to the liver cells, where 25-hydroxycholecalciferol is formed. The 25-hydroxycholecalciferol is then transported to the kidneys, where it is converted to 1,25-dihydroxycholecalciferol. It is this form of vitamin D that is active.

Finally, the recommended dosage remains an issue, as there is still no known protective level of vitamin D for the prevention of disease. Early studies on the effects of vitamin D focused on preventing rickets (osteogenesis disorders in children). Recent vitamin D research focuses on the immune and cardiovascular systems as well as blood sugar levels.

The role of vitamin D in health

Bone health. Vitamin D deficiency can lead to softening or malformations of the bones. In children, this condition is called rickets. In adults, this is called osteomalacia. The relationship between vitamin D and bone metabolism is more complex than one might think. Vitamin D increases blood calcium levels, aiding the absorption of calcium from food and decreasing the excretion of calcium in the urine. In addition, vitamin D can extract calcium from bones to maintain proper blood levels, and this affects bone strength.

Obviously, if our goal is to build strong bones, we do not want to allow calcium to be excreted from the bone tissue. For this reason, we need to ensure that vitamin D is either supplied or formed in the skin cells by sunlight. Any bony fish, including sardines or salmon, is potentially a rich source of both vitamin D and calcium.

Blood sugar control. Researchers have found that the risk of hyperglycemia and diabetes is higher in people with low vitamin D. More recent studies have shown that increasing the concentration of vitamin D in the body can reduce sugar levels and the risk of developing diabetes.

Immunity. Vitamin D is one of the many substances involved in the maturation of white blood cells - our first line of defense against most infections. Specifically, researchers found a link between low vitamin D levels and the risk of respiratory infections.

Vitamin D is found in foods

The list of foods containing vitamin D is short. In addition, one of the best food sources of vitamin D, it loses its benefits during processing. However, it will be easier for you if you like fish. Salmon, for example, contains only one serving of vitamin D per day. Sardines contain over 40% of the norm, and tuna contains just under 25%.

Eggs from free-range hens are a good source of vitamin D (about 10% of the norm per egg). Vitamin D is concentrated in the yolk, so eat a whole egg.

Also keep in mind that vitamin D is a very stable nutrient. It is not destroyed by most cooking methods. Scrambled eggs lose about 20% of their vitamin D. A slight loss of vitamin D can be expected when cooking in oil. Either way, most of the vitamin D will end up on your plate.

One research team found that when food was baked at 232 ° C for 10 minutes, vitamin D was almost unaffected. Another study reported that eggs baked at 163 ° C for 40 minutes lost more than half of their vitamin D. In other words, prolonged exposure may be the culprit.

Deficiency risk

The risk of vitamin D deficiency is substantial. In every age and gender group surveyed, reported vitamin D levels did not meet the daily requirement even with the consumption of supplements and fortified foods. Since vitamin D can form in sunlight, it is preferable not to exclude this source.

Worst of all, vitamin D deficiency has tripled since the 1980s. This trend is likely due to reduced sun exposure and increased use of sunscreens.

The geography of your residence also matters. The further north you go, the less likely you are to meet your vitamin D needs. North of 37th parallel, you get virtually no vitamin D from natural sunlight during the winter months. The darker the skin, the less efficiently you synthesize vitamin D. Therefore, people with dark color skin is better to live closer to the equator.

Sunscreen interferes with the production of vitamin D in the skin. One research team found that applying SPF8 sunscreen as recommended completely blocked vitamin D production.

Diseases with deficiencyvitamin D

• Osteoporosis
• Rickets
• Osteomalacia
• Imbalance
• Diabetes
• Rheumatoid arthritis
• Bronchial asthma
• Depression
• Epilepsy
• Weak immunity

Relationship with other nutrients

As mentioned above, the activity of vitamin D and is very closely related. There is evidence to suggest that vitamin D in the absence of adequate calcium in the body can lead to bone loss by increasing the rate of calcium resorption.

Vitamin D also appears to slightly increase intestinal absorption of magnesium. Since calcium and magnesium compete with each other for absorption, magnesium deficiency can be considered an aggravating factor. Vitamin D and vitamin K work together in bone metabolism. Low levels of vitamin K pose a risk of bone problems.

Risk of toxicity

The acceptable upper limit for vitamin D is 4000 IU for adults. Considering that it is quite difficult for many people to reach the 400 - 800 IU norm, this is not so scary. As an example, you need to eat a pound of salmon a day in order to reach a normal level.

In 2010, the U.S. National Academy of Sciences updated its vitamin D intakes.

• 0-12 months: 400 IU (10 mcg cholecalciferol)
• 1-70 years: 600 IU (15 mcg cholecalciferol)
• 70+ years: 800 IU (20 mcg cholecalciferol)
• Pregnant women: 600 IU (15 mcg cholecalciferol)
• Breastfeeding women: 600 IU (15 mcg cholecalciferol)