Vitamin D - basics, supply and benefits

Vitamin D - Grundlagen, Versorgung und Nutzen

Vitamin D belongs to the group of fat-soluble vitamins. Strictly speaking, vitamin D is not a real vitamin. It's actually a hormone, more specifically a pro-hormone. Alongside vitamin K, vitamin D is the only vitamin that the body can produce itself. For this, however, he needs the help of the sun's rays, specifically the UVB radiation. When high-energy rays of the sun hit our skin, the body forms the precursor of the hormone vitamin D with the help of cholesterol.

About 90-95% of vitamin D is formed through the skin.

Vitamin D is classified into two forms. The D3, also called cholecalciferol or colecalciferol. It is converted into the active hormone calcitriol in the liver and kidneys. In addition, the body can store vitamin D3 in adipose tissue, the so-called storage form of vitamin D, calcifediol (also 25-hydroxyvitamin D or 25-OH vitamin D).

Only in midsummer is the sun's radiation strong enough to boost vitamin D synthesis (in our latitudes).

The other form is the lesser-known D2, too called ergocalciferol. The D2 metabolism here is the same as with vitamin D3.

How much vitamin D does a person need?

Vitamin D must be determined by means of a blood analysis. Here the storage form of vitamin D, namely the 25OHD (25HD), is measured. The result is then usually given in ng/ml.

The values can be classified as follows:

  • <11ng/ml: There is a severe vitamin D deficiency here
  • <20ng/ml: There is a vitamin D deficiency here
  • 30-60ng/ml: referred to as normal supply
  • 60-90ng/ml: This is an above-average supply
  • >140ng/ml: Hhere lies Vitamin D poisoning is present (hypervitaminosis)

Tip: Try to have your vitamin D level checked once a year, at the beginning of winter. If there is a deficit or a severe oversupply, you should consult a doctor.

On a summer day, the body can produce 20,000 IU of vitamin D itself

In the case of supplementation, the vitamin D content is usually given in IE (English: IU), this stands for international units and is the content of vitamin D. 1 IU = 0.025ug. Example: 5ug vitamin D = 200 IU.

Tip: Do not take vitamin D in the evening as it can affect melatonin synthesis.

A daily intake (skin, food + supplements) of 200 to 400 IU is considered sufficient to ensure basic care.

What is the role of vitamin D in the body?

Vitamin D is essential, i.e. vital, because it is involved in over 30 metabolic processes in the body. It is often associated with healthy bones because it promotes calcium storage in the bones. One reason why infants and young children are often given extra vitamin D.

Today we know that many body cells have receptors own, that react with vitamin D. These include the immune system, muscles, skin, sexual organs, vessel walls, liver, kidneys, nerve cells, and intestines, to name just a few. These receptors could be detected in up to 36 types of tissue. A clear indication of the diverse functions and importance of vitamin D for our body.

The following health-promoting effects are now recognized by the European authority.

  • contributes to the normal function of the immune system (physical defence).
  • contributes to the maintenance of normal muscle function
  • contributes to the maintenance of normal bones
  • contributes to the normal absorption/utilization of calcium and phosphorus
  • contributes to a normal calcium level in the blood
  • contributes to the maintenance of normal teeth
  • has a role in cell division
  • is needed for healthy growth and bone development in children
  • contributes to the normal function of the immune system in children
  • helps reduce the risk of falls associated with postural instability and muscle weakness. Falls are a risk factor for fractures in men and women aged 60 and over (at 20 µg/day)

However, the effect is much more extensive, as the latest research reports show. 

Groceries with a high vitamin D content.

Foods that contain a lot of vitamin D are rather rare, and the vitamin D content also differs greatly in relation to the two variants D2 and D3.

  • Vitamin D2 is mainly found in plants such as mushrooms 
  • Vitamin D3 is mainly found in animal products such as fish, various dairy products and liver

Overall, it can be difficult to get your vitamin D needs from food. As already mentioned, 90-95% of our needs are formed through the skin.

Vitamin D supply in the population.

Our modern lifestyle has made vitamin D deficiency an ever-increasing problem. Where people used to spend hours outdoors to work, many are now indoors during the day. Be it in the office, shopping centers or other covered places. And when we do go outside, it is usually fully clothed or, in summer, with sunscreen on.

According to studies [1], the annual average of vitamin D in people in our regions is below 20ng/ml for 57% of all those involved. People over the age of 65 are even worse affected with a share of 73%.

A worldwide comparison [2] of data shows large differences depending on countries and regions. It is less common in Northern Europe and Southeast Asia. The average vitamin D intake in Scandinavia is 200-400IU/d, twice as high as in other European countries. Risk groups are young children, the elderly, pregnant women.

Vitamin D overdose and underdose.

As with all nutrients, optimal supply is important. A lot helps a lot, however, is usually the wrong approach because an oversupply of vitamin D can also entail health risks.

A vitamin D overdose leads to over-stimulated calcium absorption in the intestine and calcium absorption from the bones and consequently to a hypercalcaemia. With vitamin D production via the skin, no overdose can take place because the body regulates its own synthesis.

Attached is an overview of health risks of oversupply:

  • Headache, nausea, vomiting, dizziness
  • loss of appetite
  • muscle incoordination
  • kidney damage by calcium deposits
  • Long-term hypercalcaemia can lead to calcium deposits in soft tissues such as blood vessels, heart, lungs, muscles and tendons.

and an overview of the health risks of undersupply:

  • Diabetes
  • rickets
  • rheumatism
  • osteoporosis
  • bone and muscle wasting
  • Parkinson
  • Tuberculosis
  • lung diseases

It is therefore essential to keep an eye on your vitamin D level and always try to be in an optimal range.


[1] Vitamin D status among adults in Germany--results from the German Health Interview and Examination Survey for Adults (DEGS1) [Pubmed]

[2] Vitamin D status and nutrition in Europe and Asia [Pubmed]

Riva Verlag: The healing power of vitamin D by Nicolai Worm (ISBN 978-3-86883-888-6) - Vitamin D []