Dietary supplements: taking vitamin D supplements – when it makes sense and when not

Anyone who is only occasionally on the social networks Instagram or Tiktok will hardly be able to avoid advertising for the intake of vitamin D.

Dietary supplements: taking vitamin D supplements – when it makes sense and when not

Anyone who is only occasionally on the social networks Instagram or Tiktok will hardly be able to avoid advertising for the intake of vitamin D. Many influencers advertise the positive effects on health and suggest that taking dietary supplements with vitamin D is essential, especially now in the dark season, to stay healthy. It is true that an adequate supply of the sun vitamin is important for bone metabolism. But not everyone should simply take such vitamin supplements on their own - an overdose can be dangerous. When it makes sense to take food supplements, how much vitamin D we need and what happens in the event of an overdose.

Vitamin D plays an important role in bone metabolism. Because: We need calcium for stable teeth and bones. Our body stores it as calcium phosphate. Vitamin D supports the absorption of calcium from the intestine into the blood and its storage in the bones. It also regulates calcium and phosphate metabolism. Vitamin D is also involved in other metabolic processes.

The best way to ensure a supply of vitamin D is through the skin's own synthesis, writes the Federal Institute for Risk Assessment (BfR) and the German Society for Nutrition (DGE). So that we can absorb enough vitamin D through the skin, we have to spend enough time outdoors during the warm season.

For adequate care, the DGE recommends exposing your face, hands and arms to the sun two to three times a week between March and October and without sunscreen (10 to 25 minutes). But beware: avoid sunburn at all costs! According to the BfR, we absorb 80 to 90 percent of our vitamin D requirement through self-synthesis with sufficient sun exposure through the body's own production in the skin. In the winter months, our body then falls back on vitamin D stored in muscle and fat tissue. If the reservoirs are sufficiently full, this supply is completely sufficient to get through the winter without a shortage.

Only a very small part of the vitamin D requirement can be met through diet. It is mainly found in fatty sea fish such as salmon, herring or mackerel. Vitamin D is also found in egg yolk, liver and some edible mushrooms.

According to data from the Robert Koch Institute (RKI), most Germans are far from having a clinical vitamin D deficiency that would impair their health. After evaluating data from the years 2008 to 2011 and from 2003 to 2006 (for children and adolescents), the RKI assumes that 15.2 percent of adults and 12.5 percent of children are deficient in vitamin D.

The RKI informs that a vitamin D deficiency is only spoken of when vitamin D is lacking in the body over a longer period of time and symptoms such as softening bones occur. The level of vitamin D in the blood is subject to seasonal fluctuations. A low vitamin D value measured once does not necessarily mean that a vitamin D deficiency has been present for some time.

Vitamin D deficiency can have serious consequences for bone health. "The most serious consequences are decalcification and ultimately softening of the bones. In infants and children, this can lead to the clinical picture of rickets, which means serious disruption to bone growth and permanent deformation of the skeleton, including abrasions in the area of ​​the growth plates," says the RKI. Other signs in children are reduced muscle strength and susceptibility to infections.

Adults with a vitamin D deficiency can experience bone pain, muscle weakness, and deformity of load-bearing bones. These symptoms are caused by decalcification of the bone. Vitamin D deficiency can also contribute to the development of osteoporosis. With this disease, the bones become porous and break easily.

Some people have an increased risk of developing a vitamin D deficiency because they rarely or never spend time outdoors. These include, for example, people in need of care and those who are bedridden. With increasing age, the self-production of vitamin D decreases, which is why they are generally at risk of developing a deficiency, according to the RKI.

Babies are also at increased risk of vitamin D deficiency because they should not be exposed to direct sunlight. Even those who only go outside with covered skin and people with chronic gastrointestinal, liver or kidney diseases or those who take medication that impairs vitamin D metabolism belong to the risk group. People with darker skin are also at increased risk. Due to the increased melanin content in the skin, the UVB rays in the sun are blocked more effectively.

In dietary supplements we encounter the sunshine vitamin as cholecalciferol (D3) or ergocalciferol (D2). According to the NRW consumer advice center, vitamin D3 is mostly obtained from wool fat and vitamin D2 is obtained from the UV irradiation of ergosterol from yeast. According to the DGE, such food supplements should only be used if the vitamin D status cannot be improved either by the skin's own synthesis or by nutrition. The reason: Vitamin D is a fat-soluble vitamin, which means it can be stored in fat and muscle tissue. Taking vitamin D supplements in excessively high doses can lead to an acute or gradual overdose.

If the supply through self-synthesis and through food is not sufficient, the DGE recommends taking vitamin D supplements in a daily dose of only 20 micrograms per day. "Higher doses should only be taken under medical supervision and taking into account the individual vitamin D status. For over-the-counter food supplements, there are currently no binding maximum levels for the vitamin D content, either at national or international level," inform the experts at the DGE. Taking vitamin D supplements can make sense for risk groups, but taking them should always be discussed with a doctor.

According to the BfR, a daily intake of vitamin D preparations in doses of 50 or 100 micrograms does not make sense from a nutritional point of view. However, the authority classifies it as unlikely that there will be any adverse health effects from the occasional intake of such high-dose preparations. However, anyone who takes long-term and daily high-dose vitamin D preparations is taking an increased health risk - this is indicated by the current study situation.

"While poisoning cannot be caused by the body's own vitamin D formation and natural nutrition, it is possible through excessive intake of dietary supplements or high-dose medicines (...)," writes the RKI.

If you take too much vitamin D, it leads to an increased calcium level. In acute cases, this leads to abdominal cramps, vomiting, nausea and loss of appetite. In severe cases, it can even lead to cardiac arrhythmias, kidney damage, unconsciousness and death. Because vitamin D is stored in the body, not only an acute but also a gradual overdose can occur.

Sources: Consumer Center NRW, BfR, RKI, DGE 1, DGE 2, DGE 3

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