Vitamin D is essential for maintaining healthy bones and building muscle. The issue of vitamin D supplementation and when testing for a deficiency might be helpful is still contested among medical professionals.
The body produces vitamin D itself. Therefore, it is not really a vitamin, but rather a hormone. The most important forms are vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol).
Vitamin D promotes the absorption of calcium and phosphorous in the intestines. It therefore regulates the absorption of minerals and calcium levels in the blood. It also supports the development of the muscles, bones and teeth and strengthens the immune system.
80–90% of vitamin D in the body is produced via the skin. Vitamin D3 is developed through UVB radiation. This travels in the blood to the liver and the kidneys, where it is converted into vitamin D (calcitriol). 20–30 minutes of exposure to the sun per day is normally sufficient to produce the vitamin D we need.
Sunscreens with an SPF of 20 and higher block the UVB rays and thus inhibit the production of vitamin D. The production of vitamin D in the body decreases in the winter as the sun shines for fewer hours and the UV radiation is not as intense.
Nutrition plays only a secondary role in the absorption of vitamin D, with the body getting 10–20% of its vitamin D from food. The main sources of vitamin D are foods of animal origin. Some plant-based products also have a high vitamin D content.
Foods rich in vitamin D include:
Your daily requirement varies depending on age:
15 micrograms of vitamin D are contained for example in 180 grams of wild salmon, 515 grams of raw chicken eggs (equivalent to approximately nine medium-sized eggs) or 485 grams of fresh porcini.
According to the Federal Office of Public Health (FOPH), someone has a vitamin D deficiency if the 25-hydroxyvitamin D concentration in their blood is less than 50 nanomoles per litre of blood serum. A level below 25 nmol/l is considered a severe deficiency.
Experts disagree on what constitutes a vitamin D deficiency, however, so these figures should be treated with caution. Some experts think that deficiencies are systematically overestimated, as the reference value of 50 nmol/l is only an average across the year. The body can store a certain amount of vitamin D in the summer which can then last through the winter.
There is no conclusive evidence that regularly testing vitamin D levels among the general population is helpful. The FOPH therefore does not recommend general screening as a preventive measure. According to the FOPH, in most cases it is not necessary to measure someone’s vitamin D levels before they take supplements – as long as they do not exceed the recommended daily amount of 600 IU for adults and 800 IU for those aged 60 and over. These recommendations are supported by recognised medical publications. A test is only considered useful for high-risk groups. These include those who are pregnant, newborn babies, older people with osteoporosis or bone fractures and patients with chronic kidney or liver disease.
Vitamin D supplements are available in a variety of forms, from tablets and capsules to drops and fortified foods.
Even if you are not in a high-risk group and don’t have a diagnosed vitamin D deficiency, there is no harm in taking vitamin D supplements if you think you might be deficient. However, you should not exceed the recommended daily amount of 600 IU/15 µg for adults and 800 IU/20 µg for those aged 60 and over. The health benefits of vitamin D supplementation in this context remain debatable. Numerous studies indicate that it has no impact on the risk of suffering cardiovascular disease, cancer, bone fractures or depression.
No study has yet conclusively shown a causal link between vitamin D levels and the severity of COVID-19 infection.
If you have been diagnosed with a severe vitamin D deficiency, you should discuss taking supplements with your doctor, including how much to take.
Only the excessive consumption of supplements can cause a spike in vitamin D levels. This results in an excessive concentration of calcium in the blood, which manifests itself in a general feeling of weakness, headache and cardiac arrhythmia. In serious cases, taking too much vitamin D can lead to kidney stones and kidney failure. You should therefore avoid taking multiple vitamin D supplements at the same time.
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