Especially now, during the darker months, many people are worried about their possible insufficient vitamin D supply. Some people therefore turn to nutritional supplements. But does taking such preparations really make sense?
The human body produces most of the required vitamin D itself in the skin with the help of the ultraviolet component (UV) of solar radiation. Since the sun shines less in autumn and winter, some people turn to dietary supplements to ensure their vitamin D supply. The Federal Institute for Risk Assessment (BfR) explains in an article (PDF) for whom this can be useful.
Sunlight is not enough in winter
As the experts write, vitamin D plays an important role in calcium and phosphate metabolism and thus in the development and maintenance of healthy bones. It also strengthens muscle strength and contributes to a well-functioning immune system. A sufficient supply of this vitamin is therefore important.
Vitamin D can be produced in human skin under the influence of sunlight. With sufficient exposure to sunlight, the body’s own production contributes around 80 to 90 percent of the vitamin D supply.
However, in this country in autumn and winter there is not enough sunlight to produce enough vitamin D through the skin. So do we need vitamin D supplements at least during the dark season?
Vitamin D is stored
This question can not be answered generally. Our body stores vitamin D in fat and muscle tissue. Through physical activity, the vitamin can be released from these stores and contribute to the vitamin D supply in winter.
Sufficient time outdoors with sufficient sun exposure to the skin, physical exercise and activity, as well as a balanced diet with fatty fish (e.g. salmon or herring) at least twice a week generally ensure a good supply of vitamin D to the body.
As the BfR explains, there is good coverage with serum values from 50 nanomoles per liter, corresponding to 20 nanograms per milliliter.
However, sufficient vitamin D levels are not always achieved through the body’s own production; this depends, among other things, on sun exposure, age and skin type.
Therefore, additional intake of vitamin D can be useful for certain risk groups, especially in the winter months.
Groups at risk for insufficient vitamin D supply
According to the BfR, the risk groups for an insufficient vitamin D supply include people who hardly or not at all spend time outdoors or – for cultural or religious reasons – only go outside with their bodies completely covered.
In addition, people with dark skin are among the risk groups because, due to the high content of the skin pigment melanin, they can produce less vitamin D than people with light skin.
Another important risk group can be older people, as vitamin D production decreases significantly with age. In the older population there are often people with restricted mobility, chronic illnesses and people in need of care who hardly or cannot move outdoors at all.
No general recommendation
However, according to large clinical studies, people with adequate levels of vitamin D in their blood have no additional benefit from taking vitamin D.
People with adequate status who received additional vitamin D in these studies were no less affected by, for example, cancer, type 2 diabetes, cardiovascular diseases and bone fractures as well as falls than people who did not take a vitamin D supplement received.
A general recommendation for vitamin D supplementation to prevent illness cannot be justified based on the currently available scientific data. However, a vitamin D deficiency should definitely be avoided.
For higher doses, seek medical advice
According to the BfR, anyone who wants to supplement vitamin D should use dietary supplements with up to 20 µg of vitamin D (800 international units) per day, as this dose can also be used for long-term use and taking into account other sources of vitamin D (e.g. fortified foods). is not associated with any health-related effects.
With this dose, an adequate vitamin D serum concentration of 50 nmol/L (20 ng/ml) can generally be achieved without any sun exposure to the skin.
However, high-dose vitamin D preparations should only be taken under medical supervision.
Too high doses pose health risks
In various studies, when an additional 100 µg (4,000 IU) of vitamin D was administered daily over a longer period of time, a greater decrease in bone density in older women, an increase in the risk of falls and a deterioration in heart function in people with heart disease were observed compared to the control.
After ingesting excessively high doses, case reports reported vitamin D poisoning in children and adults, which required intensive care treatment and in one case even led to irreversible kidney damage requiring dialysis.
The BfR warns that high-dose dietary supplements with a vitamin D dose of 4,000 international units (100 µg) or more per daily intake recommendation have the potential to cause overall intake levels of vitamin D that are harmful to health if taken over a long period of time. (ad)