What is the recommended daily dose of vitamin D?

Vitamin D is one of the most peculiar nutrients. It represents a group of four fat-soluble vitamins, standing out from the other three due to its unique properties. One of the most important features that makes vitamin D unique is that the body can produce it when the skin is exposed to sunlight.

1. How is vitamin D produced in the body?
2. How does vitamin D work?
3. How much vitamin D should you consume daily?

How is vitamin D produced in the body?

Vitamin D occurs in nature in two forms, namely ergocalciferol and cholecalciferol (vitamins D2 and D3, respectively). The D2 form is characteristic of organisms such as fungi, while D3 is found in animal organisms.

Its production by humans depends on regular exposure to the sun when the sun's rays reach their peak in terms of the ratio of UVB to UVA radiation. A large amount of UVB rays (with a wavelength of 290-320 nanometres) reaching the skin activates the conversion of 7-dehydrocholesterol to a precursor of vitamin D3, which is then converted into biologically active cholecalciferol. It binds to the vitamin D transport protein, which enables the delivery of this compound to the target tissues.

How does vitamin D work?

After being produced or consumed with food, vitamin D must reach locations in the body where specific enzymes and receptors are present. The liver converts vitamin D into 25(OH)D, which is the main form circulating in the body. The final form of this compound, which actively interacts with human cells and performs regulatory functions, is 1,25(OH)₂D.

It is mainly produced by the kidneys, but it can also be produced in epithelial and immune cells, as well as in the parathyroid glands. Vitamin D is described as a transcription factor, which means that it acts by participating in the regulation of gene expression. Its action covers the skeletal, nervous, muscular and immune systems, as well as the digestive system.

How much vitamin D should you consume daily?

One of the important elements in estimating the daily requirement for vitamin D is to test its level in the body. The 25(OH)D form is used for laboratory assessment of vitamin D status. Values in the range of 30–50 ng/ml suggest that the recommended dosage for the general population of approximately 15 µg (600 IU – international units) of cholecalciferol per day can be maintained. If the diagnostic test results indicate deficiencies, supplementation should be considered.

Both people with deficiencies and those with certain health disorders often take doses of up to 50 µg (2000 IU) per day, but such supplementation is recommended under the supervision of a doctor or specialist.

The need for supplementation is increasingly being highlighted, as periods of optimal sunlight exposure and skin synthesis of vitamin D are usually spent at work (adults) or playing games (children). The autumn and winter months are the absolute recommendation for supplementation (for people who avoid fish, eggs or mushrooms).