Status: 28.05.2024 14:11

Because almost everyone has a vitamin D deficiency in the winter months, experts recommend taking additional vitamin D. Otherwise, symptoms such as decreasing bone stability and immune deficiency may occur.

Of course, it depends on the extent of the vitamin D deficiency – but experts agree: In winter, it seems sensible to take it as a dietary supplement. The recommended maximum amounts should under no circumstances be exceeded.

Vitamin D: Important for bones, metabolism and immune system

Vitamin D is essential for bone health: only with sufficient levels does the intestine absorb calcium, which is needed for bone formation,. If vitamin D is lacking, calcium is not stored in the bones, but is released from the bone substance to keep the calcium level in the blood constant. If this happens over a long period of time, bone density decreases. The substance is also involved in many important metabolic processes in the body and is partly responsible for a functioning immune system.

Symptoms: Decreasing bone stability and immune deficiency

In people who, according to the Robert Koch Institute, are “not sufficiently” supplied with vitamin D, the deficiency is minor and does not cause any health problems. However, a severe and long-term deficiency can have serious consequences:

  • Weak bones: A mineralization disorder of the bone caused by a severe vitamin D deficiency can result in the bone being less stable and resilient, leading to faster bone fractures and delayed healing. Doctors assume that with an adequate supply of vitamin D, up to 25,000 hip and femoral neck fractures could be prevented every year.
  • Weakened immune system: There are vitamin D receptors in almost all organs and tissues of the body, so this hormone influences metabolism in many places. Scientists have been able to prove that sufficient vitamin D also protects against respiratory infections. Experts assume that vitamin D has a decisive influence on the function and activity of certain defense cells: The substance appears to be responsible for activating T lymphocytes and stimulating them to divide. After contact with a pathogen, they form vitamin D recognition proteins on the cell surface. Contact with the vitamin then leads to a strong proliferation of T lymphocytes, which help to defend the body against pathogens.

Absorption of vitamin D through sun and food

The body produces the largest proportion through the sun’s UVB rays. In addition, Vitamin D can be obtained through certain foods – for example by eating fatty fish, dairy products or eggs. But even with a very healthy and balanced diet, you can only cover 10 to 20 percent of your daily requirement through food.

Causes: Vitamin D deficiency due to insufficient sun exposure

Until the age of industrialization, people were usually outside the whole time during the summer months. This meant that their vitamin D reserves were at their maximum in the autumn, which helped them get through the winter well. Nowadays, many people work indoors even in the summer, and to protect themselves from skin cancer, they use sunscreens with high sun protection factors and avoid direct sunlight.

The vitamin D absorbed in this way is usually enough to ensure an adequate vitamin D supply in the summer months. However, the vitamin D stores are not filled optimally, and a deficiency occurs in winter at the latest.

At what values ​​do we speak of a deficiency?

The vitamin D level in blood serum is expressed either in nanomoles per liter or in nanograms per milliliter. Serum levels of less than 30 nmol/l (less than 12 ng/ml) indicate an inadequate vitamin D supply with an increased risk of diseases such as osteomalacia and Osteoporosis. Experts consider serum levels of 30 to under 50 nmol/l (12 to under 20 ng/ml) to be a suboptimal supply with possible consequences for bone health. Experts describe levels above 50 nmol/l (12 to under 20 ng/ml) as an adequate vitamin D level.

Taking vitamin D: Useful in winter

Because so many people do not have sufficient vitamin D, experts recommend taking additional vitamin D during the winter months. However, determining vitamin D levels beforehand is not absolutely necessary for most people.

The German Nutrition Society recommends 800 international units (IU) daily – but many experts find slightly higher amounts to be quite sensible. Overall, however, the daily intake of vitamin D should not exceed 4,000 IU. The European Food Safety Authority (EFSA) specifies this value as the maximum upper limit. Important: This upper limit is the maximum daily recommended total intake – it also includes the vitamin D that you get from sunlight and diet (additional vitamins are often added to many foods, this should also be taken into account). Vitamin D as a dietary supplement can be taken in the form of tablets or drops.

Determining vitamin D levels through a blood test can be medically useful for people with chronic illnesses or certain symptoms. However, vitamin D tests are only of limited value due to fluctuating results, but they do provide a rough guide.

Taking too much vitamin D is dangerous

In general, too much vitamin D is harmful. Unlike water-soluble vitamin C, the body cannot simply excrete excess vitamin D, but stores it. As a result, too high a vitamin D intake can lead to an acute or gradual overdose. The result can be calcification in organs – for example in the kidneys in the form of kidney stones. Only in rare cases and with certain diseases can an extreme vitamin D deficiency occur. In these cases, it can be useful to take higher doses of vitamin D for a short period of time and only after consulting a doctor. In this case, higher-dose preparations with 10,000 or 20,000 IU are prescribed for weekly intake, for example.

Medications can affect vitamin D production

Certain medications such as cortisone, diuretics, sleeping pills and anti-epileptics can impair the effect of vitamin D (or in some cases increase it). Anyone who takes medication on a long-term basis should therefore definitely discuss the use of vitamin D supplements with their doctor.

Anyone who is prone to the formation of calcium-containing kidney stones or who suffers from kidney failure, sarcoidosis or parathyroid disease should also discuss taking vitamin D with their doctor. During pregnancy, vitamin D supplements should only be taken if there is a proven deficiency and under monitoring of calcium levels, as an increased calcium concentration in the blood can harm the unborn child.

Risk groups that often suffer from vitamin D deficiency

There are people who are particularly at risk of developing a severe vitamin D deficiency. Those affected should take appropriate amounts in consultation with a doctor. These include:

  • People of all ages who rarely go out because they spend the whole day sitting at their desks indoors. Chronically ill people and those in need of care who rarely spend time outdoors are also at risk.
  • Dark-skinned people, because the higher melanin content of their skin provides greater protection against UVB radiation
  • People who, for cultural or religious reasons, only go outside with their bodies completely covered
  • Smokers
  • High-performance athletes because they consume more vitamin D
  • People who are severely overweight – Vitamin D accumulates in fatty tissue
  • People who suffer from chronic gastrointestinal, liver or kidney diseases or who take medications such as anti-epileptics or cytostatics that affect vitamin D metabolism

Experts on the topic

Further information

Tablets of different shapes and colors © fotolia.com Photo: motorlka

Dietary supplements can lead to an overdose of vitamins and minerals – with dangerous consequences. more

Ampoule with blood sample for vitamin D test © fotolia.com Photo: arun011

Tests of vitamin levels in the blood are often expensive. Specific tests for vitamin D or B12 are usually more useful. more

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