Vitamin D and everything you need to know about it

Vitamin D belongs to fat-soluble vitamins and naturally occurs in several foods. It is also available as a dietary supplement. However, it is mainly produced endogenously when ultraviolet rays from the sunlight reach the skin and induce the synthesis of vitamin D. [1]

From the beginning of antiquity, people have known about the substance, now known as vitamin D. The first scientific description of vitamin D deficiency was rhachitis or rickets, registered in the 17th century by Dr Daniel Whistler (1645) and Professor Francis Glisson (1650). The main breakthrough in understanding rickets was the development of nutrition as an experimental science in 1910-1930. [2]

“According to biochemists, it is actually a hormone that is produced in the body when the skin is exposed to ultraviolet radiation in sunlight. Vitamin D is dissolved in fats and produces five active substances.”[3]

Why is Vitamin D so important?

Why is Vitamin D so important?

1. It plays an important role in muscle and bone health. It not only helps to absorb calcium and phosphorus from the intestine, but also has a direct effect on muscles and bones. Therefore, it can prevent and treat muscle and bone pain, chronic fatigue and osteoporosis.

2. It can also prevent immune system disorders such as asthma, rheumatoid arthritis, type 1 diabetes, Crohn’s disease or sclerosis. By strengthening the immune system with vitamin D, we can also prevent colds, flu and other infections.

3. Regulates the growth of both normal and tumour cells. For this reason, it can play an important role in the prevention and treatment of various cancers, particularly colon, prostate, pancreas and breast cancer.

4. Stimulates insulin production from insulin producing cells in the pancreas. It also lowers insulin resistance. For this reason, vitamin D can help prevent and treat type 2 diabetes.

Why is Vitamin D so important?

5. Suppresses renin-angiotensin-aldosterone (RAAS). Renin is a chemical usually produced in the body. It leads to the production of another chemical, called angiotensin, which is responsible for maintaining blood pressure. Angiotensin also causes the release of a substance called aldosterone. It is also involved in maintaining optimal blood pressure. Collectively, this interrelated chemical system is called renin-angiotensin-aldosterone (RAAS). If RAAS is hyperactive, it causes high blood pressure (hypertension), kidney disease and heart failure. Vitamin D suppresses RAAS and can prevent hypertension or other serious diseases.

6. Affects normal skin function and can therefore be useful in the treatment of skin diseases such as psoriasis.

7. Affects tooth health and is therefore important in preventing many dental problems.

8. It is essential for normal brain development and function. Therefore, it is important in the prevention and treatment of neurological disorders such as Alzheimer’s disease, Parkinson’s disease or autism. [4]

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So, what are the biggest benefits of vitamin D?

  • demonstrably improves muscle control in older people
  • Vitamin D is closely associated with a significant reduction in the risk of colon cancer and with some possible risk reduction in other types of cancer – such as lung cancer
  • has been shown to be an important protective factor against the development of multiple sclerosis
  • used to improve mood in people suffering from chronic mental disorders
  • It also has a potential benefit in regulating glucose by promoting proper pancreatic function [4]

Vitamin D and its sources

Many people have heard about getting it out of the sun. But do we have enough vitamin D from the sun at all?


The sun is the main source of vitamin D. The amount of vitamin D obtained from the sun varies from person to person. There are several factors that affect this amount:

Geographical location – the location where you live determines how much vitamin D you can get. The further north you are from the equator, the lower the intensity of solar radiation. Therefore, your skin produces less vitamin D if you live in Nordic locations.

Season and time of day – your skin can produce more vitamin D during summer and less in winter. This is due to the fact that the surface of the Earth reaches less sunshine in winter. The best time for vitamin D synthesis is from 10:00 to 15:00.

New claims about vitamin D

Suntan lotions, dirt, shade, glass windows, clothing – all these factors reduce the amount of UV radiation that enters the skin and therefore reduce normal vitamin D production through the skin. A suntan lotion with a protection factor of 8 or more reduces the skin’s ability to produce vitamin D by more than 95%. Clouds, shadows and severe contamination reduce UV radiation by up to 50%.

Age – Compared to a young person, the skin of the elderly contains much less 7-dehydrocholesterol. For this reason, the skin of the elderly usually contains approximately 25% of vitamin D3.

Skin colour – the colour of our skin comes from a pigment in the skin called melanin. The more melanin you have, the darker the colour of your skin. Melanin serves as a natural sunshade and blocks the sun’s rays from passing into deeper skin layers. That is why darker skin is less effective in the synthesis of vitamin D from the sun compared to light skin.


Foods that naturally contain vitamin D include fatty fish – salmon, mackerel and blue fish. Vitamin D is also present in small amounts in vegetables, meat and egg yolks.

Why is Vitamin D so important?

 In 100 g food
Vitamin D in international units (IU)
Fish oil 16 000 000
Cocoa butter 120 000
Herring 48 000
Tuna 30 000
Cocoa powder 6 000
Salmon 4 000
Sardines in oil 3 000
Yolk 2 000
Mushrooms 2 000
Cream 200
Liver 40
Butter 30
Milk 30

Vitamin D and nutritional supplements

In dietary supplements, vitamin D is available in two forms – D2 (ergocalciferol) and vitamin D3 (cholecalciferol), which differ chemically only in their side chain structure. Vitamin D2 is made by yeast ergosterol UV radiation. Vitamin D3 is produced by irradiating 7-dehydrocholesterol from lanolin and chemical conversion of cholesterol. Vitamins D2 and D3 may appear to be the same in nutritional values, but vitamin D2 is less effective at high doses. D3 is the animal form and D2 is the plant form of vitamin D. Vitamins D2 and D3 are not biologically active, they must be modified in the body to have an effect. [6]

Vitamin D and nutritional supplements

Who has lack of vitamin D most often?


pregnant and breastfeeding women


women in menopause

people who have a diet poor in vitamin D

people with kidney problems

How much of vitamin D do we need?

Recommended Dietary Allowance (RDA) is the average daily dose sufficient to obtain nutrients in all healthy people.

Recommended daily dose (RDA) for vitamin D

It is expressed in International Units (IU) and in micrograms (mcg); the biological activity of 40 IU is equal to 1 mcg.

0 – 12 months400 IU (10 mcg)400 IU (10 mcg)
1 – 13 years600 IU (15 mcg)600 IU (15 mcg)
14 – 18 years600 IU (15 mcg)600 IU (15 mcg)
19 – 50 years600 IU (15 mcg)600 IU (15 mcg)
51 – 70 years600 IU (15 mcg)600 IU (15 mcg)
over 70 years800 IU (20 mcg)800 IU (20 mcg)

Overdosing of Vitamin D

Taking a very high daily dose of vitamin D, for example 50 or more times the recommended daily dose for several months, may cause toxicity. Early symptoms include loss of appetite, nausea and vomiting, excessive thirst, weakness, nervousness and high blood pressure.

Excessive amounts can also increase calcium in the blood, leading to vascular and tissue calcification, with consequent damage to the heart, vessels and kidneys. The use of calcium supplements (1000 mg / day) and vitamin D (400 IU) in postmenopausal women was associated with a 17% increase in the risk of developing kidney stones within 7 years. Excess sunbathing does not cause toxicity by vitamin D. Taking enough vitamin D from food to cause toxicity is very unlikely. [6]      

Overdosing of Vitamin D

Discovery of Vitamin D

The modern history of vitamin D began in the middle of the 1800s, when it was noted that children living in the city were more likely to have rickets than those living in rural areas. Half a century later, a scientist Mr Palm reported that children raised in a warmer climate had practically never developed rickets.

Other researchers noted that people with skin cancer had a lower incidence of another type of cancer, as well as lower overall mortality from all internal cancers in the sunnier areas. These observations were almost unnoticed, and the data stagnated until 1970, when maps with cancer mortality rates were created. A study of these maps showed Cedric and Frank Garland of Johns Hopkins University showed a strong latitudinal shift to the colon cancer mortality rate in 1980. They assumed that higher levels of vitamin D compounds and calcium intake in people in the south were responsible for a lower incidence of cancer. Edward Gorham and colleagues have conducted studies in which serum vitamin D compounds have been shown to reduce cancer risk. William B. Grant then conducted numerous environmental studies, extending the theory of vitamin D to other cancers. [7]

Discovery of Vitamin D

Vitamin D Deficiency or “English Disease”

Sir Edward Mellanby (United Kingdom) was concerned about the extremely high incidence of rickets in the United Kingdom, especially in Scotland. In fact, the disease is still known as “English disease”. After reviewing McCollum’s work, Sir Mellanby decided that rickets may be due to dietary deficiency.

He made use of the diet that was consumed daily by Scottish citizens who had the highest incidence of rickets. Their diet contained mainly oatmeal. He tried this diet on his dogs, which he kept in confined spaces and away from the sun’s rays. Dogs developed rickets that were identical to human disease. Sir Mellanby cured the disease with cod liver oil and supposed that vitamin A was responsible for preventing rickets. McCollum noticed this finding and decided to test the assumption that vitamin A is responsible for healing rickets. Through the cod liver oil, he injected oxygen that destroyed vitamin A, and thus the medicine was no longer able to prevent vitamin A deficiency but had the ability to heal rickets. McCollum concluded that the factor that cures rickets is a new vitamin called Vitamin D. [8]

New claims about vitamin D

Vitamin D is actually a hormone. It is produced in the skin from 7-dehydrocholesterol (provitamin D3), which is derived from cholesterol. This is evidence that cholesterol is not only harmful to health. The fact is that cholesterol is a precursor to most hormones in the body.

By discovering that vitamin D is a hormone, it has helped scientists discover its main effect, which is the absorption of calcium and phosphorus from the intestines.

Over the past 20 years, our knowledge of vitamin D has undergone revolutionary changes. Vitamin D plays an important role in the normal functioning of all systems in the body, such as regulation of cell growth, differentiation of cells into a specialized cell and ultimately cell death, regulation of the immune, cardiovascular and locomotor systems, and insulin metabolism.

Like other hormones, Vitamin D exerts its biological effects through a specific chemical structure within the cell, called a cell line. Vitamin D receptor (VDR), which has been detected in almost every tissue in the body. VDR is present inside the cell nucleus. Once bound to its receptor, vitamin D can affect various genes. McGill University in Canada has revealed that vitamin D can affect more than 900 genes, directly or indirectly. In this way, it regulates a wide variety of physiological processes within the cell.

Researchers have found that vitamin D deficiency is much more common than expected. In fact, it has reached a pandemic dimension worldwide. It partially explains the epidemic of chronic fatigue, osteoporosis, heart disease, hypertension, diabetes, cancer, asthma and other immunological diseases. Proper vitamin D supplementation can help prevent as well as treat most of these diseases. Unfortunately, most doctors do not take vitamin D seriously, also because it is mistakenly called vitamin D. To call a hormone as vitamin is a serious mistake which, unfortunately, continues to this day. [4]

Vitamin D is one of the most important biological regulators of calcium metabolism. Along with the two peptide hormones – calcitonin and parathyroid hormone, vitamin D is responsible for maintaining calcium balance. These three substances also play an important role in phosphorus homeostasis. [9]

New claims about vitamin D

Research findings on vitamin D

In 1923, Goldblatt and Soames unequivocally identified that when the vitamin D precursor in the skin (7-dehydrocholesterol) was exposed to sunlight or ultraviolet light, substances equivalent to the fat-soluble vitamin were created. Hess and Weinstock confirmed the statement – “light equals vitamin D”. They carved a small part of the skin, irradiated it with ultraviolet light, and then fed it with a group of rickets. Irradiated skin provided absolute protection against rickets, while non-irradiated skin provided no protection. Obviously, these animals were able to produce sufficient amounts of vitamin D by UV radiation, suggesting that this was not a dietary deficiency.

The chemical structure of these D vitamins was established in 1930 in the laboratory of Professor Adolf Otto Reinhold Windaus at the University of Gottingen, Germany. Professor Windaus had 55 PhD students and chemists working on the “Vitamin D” project. He was awarded the Nobel Prize for Chemistry in 1928 for his work on sterols and their relationship to vitamins.

Vitamin D2, which may be produced by ultraviolet radiation of ergosterol, was chemically characterized in 1932. Vitamin D3 was chemically characterized only from 1936, when it was demonstrated by the result of ultraviolet radiation of 7-dehydrocholesterol. [2]

In 1952, Carlsson and Bauer found that vitamin D had a greater effect on the mobilization of calcium from the bones into the plasma reservoir than on the deposition of minerals into the bone. However, this is not a decalcification of the bones. Vitamin D plays an important role in maintaining serum calcium, which is required not only for skeletal mineralization, but also for neuromuscular functions. This discovery defined a new use of vitamin D in increasing serum calcium. [8]

We believe that through this article we have brought you closer to vitamin D and its effects on the human body. Are you using it? If you liked the article, support it by sharing.


[1] Ryan Andrews, All About Vitamin D, – https://www.precisionnutrition.com/all-about-vitamin-d

[2] University of California, Vitamin D. – https://vitamind.ucr.edu/about/

[3] Jarmila Madžuková, Liečivá sila vitamínov a minerálnych látok, Bratislava, Príroda, s.r.o., 2014.

[4] Sarfraz Zaidi, Power of Vitamin D, United States of America, Sarfraz Zaidi, 2013.

[5] Bianka Stuppacherová, Slnečný vitamín D nám v zime chýba.– https://zdravie.pravda.sk/zdravie-a-prevencia/clanok/302456-slnecny-vitamin-d-nam-v-zime-chyba/

[6] National Institutes of Health, Vitamín D.– https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/

[7] Mohr SB, A brief history of vitamin d and cancer prevention.– https://www.ncbi.nlm.nih.gov/pubmed/19185802

[8] Hector F DeLuca,History of the discovery of vitamin D and its active metabolites, – https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3899558/

[9] Anthony W.Normani, Vitamin D: The calcium homeostatic steroid hormone, 111 Fifth Avenue, New York, Academic Press, 1979.