Vitamin D is a vitamin that is constantly being discussed. When and how much, and above all, for whom is the use of a vitamin D supplement advisable? We would like to provide you with some information on this topic.
In principle, the human organism is capable of producing all of its vitamin D requirements itself. That is why vitamin D supply in Germany is considered to be largely secure, even though the average recommended intake through food is significantly below the recommended levels.
Here are some selected foods with a corresponding vitamin D content:
It has generally been assumed that vitamin D requirements are met in most population groups through a combination of dietary intake and endogenous synthesis.
To prevent vitamin D deficiency symptoms, spending 15–30 minutes outdoors every day is sufficient. However, it should be noted that in Germany, the UVB radiation necessary for vitamin D synthesis is very low between October and April.
Difficulties therefore arise during the winter months and for certain risk groups. These include elderly and hospitalized people with low UV exposure, infants and young children, and people with dark skin.
People who suffer from chronic gastrointestinal, liver, or kidney diseases or who take medications that impair vitamin D metabolism (e.g., antiepileptics or cytostatics) are also among the risk groups.
Classic vitamin D deficiency symptoms such as rickets and osteomalacia play only a minor role today.
In view of the preventive effects of the vitamin, a higher intake appears desirable. Until now, plasma levels of the vitamin D metabolite 25(OH)D3 in the range of approximately 10 to 40 nmol/L were considered an indicator of adequate supply; these levels can be easily achieved with the current intake recommendations in combination with exposure to sunlight.
However, there are now increasing calls that this is too low from a preventive perspective. According to these calls, plasma levels of 25(OH)D3 should be at least 70 nmol/l. This means that vitamin D supplementation is necessary, especially during the winter months when there is little sunlight. Accordingly, there are recommendations to consume at least 25 μg/d of the vitamin daily.
Key findings from some study data (to be assessed individually)
- Inhibition of inflammation
- Improvement in blood sugar level regulation
- Pregnancy and behavioral problems in children
- Physical performance in children
- Improved brain function in combination with other active ingredients¹⁹
- Improved quality of life for asthma and other lung diseases²⁰
- Protective effect in liver damage²¹
- Protective effect in liver damage²¹
- Reduction in the incidence, severity, and progression of rheumatoid arthritis²³
Against the backdrop of the discussion about a significantly higher intake of vitamin D, the question arises as to whether this can be recommended without reservation from a toxicological point of view.
It is undisputed that an intake of up to 50 μg/d can be considered safe for healthy adults on a long-term basis. This value has been set by the European Scientific Committee on Foods as the upper limit for tolerable intake.
In addition to a deficiency, it is also possible to overdose on vitamin D. This is because vitamin D is a fat-soluble vitamin that can be stored in fat and muscle tissue. Critical overdoses are possible due to excessive intake of supplements, high-dose medications, high consumption of fortified foods (or a combination of these factors).
This can lead to elevated calcium levels (hypercalcemia), which can cause acute nausea, loss of appetite, abdominal cramps, vomiting, or, in severe cases, kidney damage and cardiac arrhythmia. Since vitamin D can be stored in the body, both acute and gradual overdoses are possible.
Vitamin D and COVID
The discussion about vitamin D supplementation has recently been intensified by the coronavirus pandemic and the association of more severe COVID-19 cases with lower vitamin D levels, which has led to increasingly loud calls for vitamin D supplementation.
As with respiratory infections in general, there are now numerous association studies on COVID-19 that point to a negative correlation between low vitamin D levels and a more severe form of COVID-19 (Pereira et al., 2020).
It is also certain that, given the inconsistent data available, there is insufficient evidence to indicate vitamin D therapy alone as a means of preventing or treating COVID-19 infection.
Literature
Statement by the German Society of Endocrinology on the role of vitamin D in the coronavirus pandemic February 11, 2021
Answers from the Robert Koch Institute to frequently asked questions about vitamin D. As of January 25, 2019.
DAZ online “New findings on vitamin D”
Take vitamin D on your own initiative in small doses at most
The Federal Institute for Risk Assessment (BfR) has warned of the health risks of taking vitamin D supplements on your own. “Higher doses should only be taken under medical supervision and taking into account the individual's vitamin D status,” according to a recent statement by the institute.
Anyone who wants to take vitamin D on their own initiative should only use supplements with a daily dose of up to 20 micrograms (800 international units). “At this amount, no adverse health effects are to be expected.”
According to the BfR, regular daily intake of vitamin D in high doses—without medical justification—increases the risk of health problems such as kidney stones or kidney calcification. There have also been cases of acute kidney failure as a result of uncontrolled self-medication with vitamin D supplements.
Recommendations for taking vitamin D supplements have been circulating on the internet for some time, currently also based on indications that they could prevent infection with the coronavirus or a severe course of COVID-19 disease.
According to the BfR, there are indications that insufficient vitamin D serum levels are associated with an increased risk of acute respiratory infections. However, the data on COVID-19 is currently still uncertain. In particular, it has not yet been shown that people with adequate vitamin D levels benefit from additional vitamin D supplementation.
“A general recommendation to take vitamin D supplements to prevent SARS-CoV-2 infection or severe COVID-19 disease is therefore not justified at present.”
The institute advised that the best way to ensure a good supply of vitamin D is through the skin's own synthesis. “Physical exercise and outdoor activities also strengthen muscles and bones.” In addition, it is recommended to eat fatty sea fish such as herring or salmon once or twice a week.
From the BfR's point of view, a general vitamin D intake of up to 20 micrograms per day should only be considered for nursing home residents. “This is because vitamin D is produced in the skin under the influence of sunlight. However, many older people hardly ever go outdoors.” In addition, vitamin D production decreases significantly with age.
According to this, people who spend little or no time outdoors or who, for cultural or religious reasons, always go outside with their bodies completely covered are also among the risk groups for insufficient vitamin D supply.
Due to its geographical location, vitamin D production outdoors in Central Europe is only possible during the summer months (March to October), according to the Robert Koch Institute (RKI). However, the body is able to store vitamin D reserves in fat and muscle tissue. This storage capacity also explains the dangers associated with the careless use of vitamin D supplements.
In general, an adequate supply of vitamins and minerals is important for human immune function, according to the BfR. “In times of increased activity of viral colds and respiratory diseases, a varied diet with plenty of vitamin- and mineral-rich fruit and vegetables is therefore particularly important.” Additional supplementation with dietary supplements is generally not necessary in this country.
Literature
Statement by the German Society of Endocrinology on the role of vitamin D in the coronavirus pandemic. February 11, 2021
