Vitamin D

Vitamin D belongs to the group of fat-soluble vitamins. This component plays an extremely important role in the human body and is necessary for proper functioning. Unfortunately Vitamin D deficiencies in society are very common, which contributes to disorders of the entire system.

What is vitamin D?

Vitamin D belongs to the group of fat-soluble, steroidal, organic chemical compounds. There are several forms of vitamin D, but most often we focus on:

  • vitamin D2, called ergocalciferol,
  • vitamin D3, or cholecalciferol.

The bioavailability of vitamin D, as well as vitamins A, E and K, is closely related to the presence of fats in food intake. In addition, fat-soluble vitamins are not excreted from the body in the urine, but remain stored in the body, more specifically in the liver and adipose tissue. Therefore, there is a risk of exceeding the demand for this ingredient, which may result in serious consequences.

Vitamin D enters the body in two ways. Together with food or by way of skin synthesis.

The component is synthesized under the influence of ultraviolet rays. The precursor of vitamin D (7-dehydrocholesterol) is formed in the skin from cholesterol. It undergoes changes in the liver, and the active form of vitamin D is synthesized in the kidneys. For the formation of active vitamin D, parathyroid hormones such as parathyroid hormone or PTH are necessary.

Vitamin D sources

Human body itself can synthesize vitamin D, which is produced in the skin due to exposure to UVB sunlight. A good source of vitamin is therefore the sun.

However, this ingredient can also be found in food. The source of vitamin D2, which is an ingredient of plant origin, is usually fortified foods, yeast and mushrooms. Sources of vitamin D3, a compound of animal origin, include egg yolks, liver and butter.

Also other foods are distinguished by the richness of this ingredient. The most vitamin D can be found in foods such as:

  • fatty sea fish (especially fresh eel, herring in oil and roasted salmon),
  • caviar,
  • fish oils,
  • cheese,
  • cow milk.

Despite the wide access to vitamin D, both from food and UVB radiation, additional supplementation of this ingredient is often recommended, resulting from commonly occurring deficiencies.

The role of vitamin D in the human body

Vitamin D is a key ingredient necessary for the work of the whole body, because it affects many functions and processes taking place in the body, i.e.:

  • supports the regulation of calcium-phosphorus metabolism, being responsible for the proper absorption and use of calcium and phosphorus,
  • supports the functioning of the immune system,
  • is responsible for proper development,
  • affects bone mineralization, which determines the proper development of the skeletal system,
  • strengthens teeth and muscles, including the heart muscle,
  • supports the work of the circulatory system,
  • participates in the regulation of HDL cholesterol,
  • participates in the process of cell division,
  • is responsible for the proper functioning of the nervous system,
  • affects the level of glucose and regulates the release of insulin,
  • has a huge impact on well-being,
  • is responsible for the synthesis of testosterone, so it has an effect supporting the building of muscle mass.


Vitamin D3, compared to vitamin D2, is more effective and resistant to temperature changes.

In addition, as we mentioned earlier, the assimilation of vitamin D depends on the supply of fats in the diet. Fats facilitate its absorption and increase the efficiency of absorption.

In addition, the bioavailability of the compound increases when, along with the diet, we provide the body with adequate amounts of vitamin A and C as well as calcium, phosphorus and unsaturated fatty acids.

Vitamin D requirement

The content of vitamin D in the body can be determined by testing the concentration of 25-hydroxycholecalciferol [25(OH)D3] in the blood plasma.

Vitamin D supplementation is recommended from the first day of life. In infancy, it is recommended to give your toddler vitamin D throughout the year. At the age of 0-6 months, 400 IU of vitamin D per day should be supplied to the child's body, regardless of the method of feeding, while in the second half of life this value should oscillate between 400-600 IU per day, depending on the daily amount of vitamin D taken with food.

Among older children, the recommended dose is 600-1000 IU per day, while adolescents and adults should supplement vitamin D in the amount of 800-2000 IU. The specific portion of the preparation depends on body weight, vitamin D supply along with diet and daily exposure to sunlight.

In old age the metabolism of vitamin D changes and the absorption of the component from food decreases. Thus, among the elderly, year-round supplementation with vitamin D is recommended. Unfortunately, vitamin D deficiencies in society are very common, which contributes to disorders of the entire system.

Proper supplementation is extremely important so as not to lead to both deficiencies and excess of the ingredient intake. The supply of vitamin D is recommended throughout the year, although in the autumn and winter period, particular attention should be paid to covering the demand for this compound.

Symptoms of vitamin D deficiency in the body

Vitamin D deficiency can contribute to chronic fatigue. Other symptoms of insufficient supply of the ingredient include sleep disorders, increased susceptibility to infections, frequent bone and muscle pain and increased hair loss. Vitamin D deficiency also hinders the process of wound healing and recovery after all kinds of injuries.

Long-term deficiencies of vitamin D in the body can contribute to a decrease in immunity, coronary heart disease and problems in the functioning of the nervous system, as well as to disorders of skeletal development, osteoporosis and bone softening (osteomalacia).

Vitamin D deficiency in children may promote growth disorders, slow growth of the fontanel and bone curvature.

Excess vitamin D

Although it is often said about insufficient supply of vitamin D, few people realize that its excess is also unfavorable for the body's work.

Symptoms of excess vitamin D include loss of appetite, nausea, vomiting and diarrhea. In addition, increased intake of the component leads to weakness of the body and excessive irritability. Excess vitamin D also contributes to an increase in blood pressure, confusion, muscle and joint pain.

Long-term, increased vitamin D intake can lead to serious health effects i.a. kidney damage, heart and pancreatic disorders.

Excessive consumption of the ingredient with food or an overdose of vitamin D under the influence of solar UV radiation seems unrealistic. However, providing too large portions of the compound in the form of a dietary supplement is quite possible.

That is why before starting to take vitamin D in the form of supplements, it is recommended to consult a doctor and perform the necessary tests i.a. it is worth finding out what is the level of vitamin D in our body.

It is also important not to exceed the recommended portions of the product and to follow the information on the packaging or leaflet of the preparation.

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