What is vitamin D anyway?

Vitamin D is actually not a vitamin at all, but a hormone that the body needs for vital processes. “About 85 to 90 percent of the body forms itself with the help of UV radiation,” explains Professor Dr. Helmut Schatz, emeritus director of the Bergmannsheil Medical University Clinic at the Ruhr University in Bochum and board member of the German Society for Endocrinology. Only a small proportion becomes over Ingested food, for example with salmon or herring, chicken eggs, mushrooms, chanterelles, veal or beef liver. “However, a sufficient supply of vitamin D cannot be achieved through diet alone. The most important thing is to go outside – preferably every day for about half an hour with uncovered hands and face, “recommends Schatz. Even when the sky is cloudy and even in winter, our bodies are able to absorb vitamin D through the skin to form – although not as much as when the sun was shining in summer.

How well are Germans supplied with vitamin D?

In recent years it has been said time and again that almost all Germans are deficient in vitamin D. However, this is not the case: According to health data that the Robert Koch Institute (RKI) collected for Germany from 2008 to 2011, a good every second adult does not achieve sufficient vitamin D values ​​of over 50 nmol / l (20 μg / l) in the blood. However, a real deficiency is only spoken of when serum values ​​are below 30 nmol / l (12 μg / l). This affected 15 percent of the study participants.

Are there any risk groups for a vitamin D deficiency?

According to the RKI, some people have a higher risk of a deficiency. This includes:

  • People who are seldom outdoors
  • Seniors over 65, as the self-production of vitamin D decreases with age
  • Infants who should not be exposed to direct sunlight
  • People who, for religious reasons, only go outside with their skin covered
  • a dark skin tone as it is less permeable to UV rays
  • People with chronic intestinal, liver or kidney diseases

Which diseases does vitamin D influence?

According to Schatz, the connection is scientifically proven in only a few diseases. These include:

  • Rachitis: In babies with vitamin D deficiency, the bones are insufficiently mineralized, they remain soft and can become deformed. To prevent this clinical picture, infants up to the end of the first year of life also receive vitamin D in the form of tablets.
  • Malabsorption in chronic intestinal diseases and chronic kidney and liver diseases: Here, too, an additional dose of vitamin D is necessary, as the body produces less vitamin D in these clinical pictures, which in turn makes the absorption of calcium more difficult.
  • osteoporosis: For a long time it was considered certain that vitamin D in combination with calcium can prevent bone loss. Opinions are now divided: “There are increasing numbers of studies that show that a dose of vitamin D and calcium has no effect,” says Schatz. Many doctors continue to prescribe it for their patients because the risks are negligible if the dosage is not too high. The RKI also writes that an insufficient supply of vitamin D can have negative consequences for bone health. The reason for this is that our body cannot optimally absorb calcium from food, which is important for stable bones, without vitamin D.

However, it has not been scientifically proven that vitamin D can help with cancer, diabetes, depression, rheumatism or heart disease. “These are only speculations based on so-called observational studies. However, such studies do not allow any conclusions to be drawn about cause and effect,” explains Schatz. Extensive work such as the VITAL study showed no evidence of such effects. In the course of the coronavirus pandemic, studies were also published that confirm vitamin D has positive effects on the course of the disease in Covid-19. “These are also observational studies. There is still no scientific evidence that vitamin D actually has an effect on Covid-19,” says the expert.

Taking Vitamin D: Yes or No?

Healthy adults who regularly go outdoors do not need to take vitamin D. If you are afraid of a deficiency, it is best to discuss this with your doctor. You usually have to pay for a blood test for vitamin D yourself – just like the dietary supplements if they are not medically necessary. Schatz emphasizes that too much vitamin D can also be harmful: “850 to 1000 international units (IU) per day are not a problem, but I strongly advise against using very high-dose preparations with 5000 or 10,000 IU.” In extreme cases, high doses of vitamin D taken over a long period of time can damage the kidneys and promote heart disease.


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