Vitamin D
and Martina Feichter, medical editor and biologistCarola Felchner is a freelance writer in the medical department and a certified training and nutrition advisor. She worked for various specialist magazines and online portals before becoming a freelance journalist in 2015. Before starting her internship, she studied translation and interpreting in Kempten and Munich.
More about the expertsMartina Feichter studied biology with an elective subject pharmacy in Innsbruck and also immersed herself in the world of medicinal plants. From there it was not far to other medical topics that still captivate her to this day. She trained as a journalist at the Axel Springer Academy in Hamburg and has been working for since 2007 - first as an editor and since 2012 as a freelance writer.
More about the experts All content is checked by medical journalists.
The term vitamin D describes a group of fat-soluble vitamins that are important for the calcium balance and the mineralization of the bones. The body can absorb the vitamin through food and also produce it itself with the help of sunlight. Read everything you need to know about the topic here: What is vitamin D good for? How much vitamin D do you need every day?
What is Vitamin D
Strictly speaking, vitamin D is not a real vitamin. According to the definition, vitamins are vital organic compounds that the body has to take in regularly with food because it cannot produce them or cannot produce them in sufficient quantities. However, this does not apply to vitamin D: With sufficient exposure to the sun, the body can produce most of the vitamins it needs (80 to 90 percent) itself. At around 10 to 20 percent, diet only accounts for a relatively small proportion of the supply of vitamin D.
Hormone precursor (prohormone) would actually be the more appropriate name for vitamin D. The body converts it into a hormone called calcitriol. It is the biologically active form of vitamin D.
What is Vitamin D3?
The collective term vitamin D includes several fat-soluble compounds. One of them is vitamin D3, also called cholecalciferol or colecalciferol. It is converted into the active hormone calcitriol in the liver and kidneys. In addition, the body can convert vitamin D3 into a storage form, the so-called calcifediol (also 25-hydroxy-vitamin D or 25-OH-vitamin D).
Vitamin D2, also called ergocalciferol, also belongs to the vitamin D group. It is converted into the more effective form of vitamin D3 in the body.
Vitamin D production with the help of the sun
The body can produce vitamin D in the skin using UV-B rays from the sun. It is the place of the body's own vitamin D production (endogenous synthesis). Vitamin D arises from two preliminary stages: provitamin D3 (produced in the liver from cholesterol) is converted into previtamin D3 in the skin under the action of UV-B rays. This is then also converted into vitamin D3 with the help of UVB light.
In winter, however, the solar radiation in our latitudes is too weak for sufficient vitamin D production in the skin. The body then - if available - falls back on the vitamin D3 stored in the form of calcifediol. The stores are mainly located in muscle and fat tissue.
What are the tasks of vitamin D in the body?
The main vitamin D function in the body is in the area of the bones:
Vitamin D (more precisely: calcitriol) promotes the formation and maturation of bone stem cells. It also regulates the absorption of calcium in the intestine and promotes the incorporation of calcium and phosphate into the bones (mineralization) - the bones become hard and strong. In addition, calcium and phosphate are also part of strong teeth.
Other, but not yet scientifically proven effects of vitamin D:
- Strengthening the immune system, both in the defense against pathogens and in the inhibition of excessive immune reactions (helpful in autoimmune diseases such as type 1 diabetes and multiple sclerosis)
- Strengthening the muscles
- Protective effect for the nerve cells in the brain
- positive effect on the cardiovascular system
- Reduction of vascular disease
- Protective effect against cancer
- Protection against rickets (this is why giving babies vitamin D is so important)
- positive effect on the psyche
What is the daily requirement for vitamin D?
The German Nutrition Society (DGE) estimates the vitamin D requirement from one year of life at 20 micrograms (µg) of vitamin D per day, according to the DGE.
According to the DGE, the vitamin D intake should be as high in the absence of the body's own synthesis:
|
age |
Vitamin D intake in the absence of endogenous synthesis (in µg / day) |
|
up to 12 months
|
10 |
|
1 to 14 years |
20 |
|
15 to 64 years |
20 |
|
from 65 years |
20 |
|
Pregnant women |
20 |
|
Breastfeeding |
20 |
To prevent rickets, infants (i.e. children up to the age of 1) regularly receive a vitamin D supplement. This ensures that the vitamin D requirement is really met - regardless of whether the child is breastfed or not and how much the body produces vitamin D itself. In the second year of life, the children should still receive the vitamin D preparation during the winter months.
For older children, adolescents and adults, it may also be necessary to supply vitamin D separately: Between October and March, the body can hardly produce any vitamin D at all because the sun is too weak and the bare skin is hardly exposed to light due to the low temperatures will. He is then dependent on the stored vitamin D. But if the storage tanks are not replenished in summer (for example because you haven't been outside in the sun enough), things will get tight. A diet with the usual foods cannot compensate for the deficit, as it provides far too little vitamin D (about 1 to 2 µg for children, 2 to 4 µg of vitamin D per day for adolescents and adults). Therefore, vitamin D deficiency is widespread in our part of the world. In this case, the DGE recommends taking a preparation with vitamin D. Children used to have to take cod liver oil, which is rich in natural vitamin D. Nowadays there are tasteless ready-made preparations (e.g. tablets, drops) with vitamin D for young and old.
Vegan people are particularly susceptible to an undersupply if they do not stay in the sun. Vitamin D is only found in significant quantities in very few plant-based foods, for example in some edible mushrooms and in margarine fortified with vitamin D.
Keyword solarium
In the cold season, many people rely on their skin being able to produce sufficient amounts of vitamin D by visiting the solarium. Instead, they run the risk of developing skin cancer:
The intensity of the UV-B rays in solariums is about the same or slightly lower than in the midday sun in the midsummer Mediterranean region. So that can be way too strong for Central European skin. In addition, the intensity of UV-A radiation in solariums is up to six times as high as in sunlight (with facial tanners even up to ten times as high). This type of radiation cannot be used in the body to produce vitamin D. Rather, it may even promote the breakdown of vitamin D, which scientific studies suggest. Above all, however, the intensive UV-A radiation in tanning beds increases the risk of skin cancer. If you go to the solarium for the first time at a young age (under 35), the risk of the dangerous black skin cancer is almost doubled.
Experts therefore advise against going to the solarium to prevent vitamin D deficiency!
Vitamin D: foods high in content
Even if our food contributes little to the supply of vitamin D, one should make sure that the diet is adequate. You can find out which foods have significant vitamin D values in the article Foods with a high vitamin D content.
How does a vitamin D deficiency manifest itself?
Insufficient sun exposure can be a cause of vitamin D deficiency as well as a disorder in the vitamin D metabolism. You can read more about this and the possible consequences in the article Vitamin D deficiency.
How does a vitamin D overdose manifest itself?
Like a deficiency, too much vitamin D can have serious consequences. However, there is practically no excess through sun exposure or diet. The situation is different with vitamin D supplements. You can find out more about the side effects of high-dose vitamin D intake in the article Vitamin D: Overdose.
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