Many people turn to dietary supplements to get their vitamin D. However, experts point out that such preparations, when taken in high doses, do not help healthy people, but in some cases they can cause harm.
Vitamin D is extremely important for health and a vitamin D deficiency can lead to various health problems. Anyone who takes nutritional supplements is not necessarily doing themselves any good. Because high-dose preparations with vitamin D can have long-term health effects. The Federal Institute for Risk Assessment (BfR) points this out in a current communication.
Sufficient vitamin D supply
Vitamin D occupies a special position among vitamins: unlike most vitamins that have to be taken in with food, the body can produce it itself, in the 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.
In the winter months from October to March, the sunlight in Central Europe is not strong enough for sufficient production of vitamin D, but the body can store the vitamin in fat and muscle tissue. It can be released again through physical activity and contribute to the supply of vitamin D in the winter months.
However, sufficient vitamin D levels are not always achieved through the body’s own production. Therefore, additional intake of vitamin D via preparations can be useful for certain groups of people, especially in winter.
It can also make sense to take such preparations for sick people or people in need of care who spend little or no time outdoors.
The range of dietary supplements containing vitamin D is huge. These also include products that contain particularly high doses of vitamin D, sometimes in combination with other substances such as vitamin K.
But high-dose dietary supplements with 100 micrograms (µg) or 4,000 international units (IU) of vitamin D or more per daily dose are not necessary for sufficient supply. They can even do harm.
“Anyone who takes such drugs over the long term risks health problems,” warns Dr. Karen Ildico Hirsch-Ernst from the BfR’s Nutritional Risks, Allergies and Novel Foods Section.
“In some clinical studies, daily administration of 100 micrograms of vitamin D over a longer period of time compared to controls has shown a greater decrease in bone density in older women, an increase in the risk of falls and a deterioration in cardiac function in people with heart disease.”
If consumed in excessive amounts, vitamin D poisoning can occur. This is shown by a pronounced increase in calcium levels in the blood. Symptoms of such hypercalcemia can include fatigue, muscle weakness, nausea, cardiac arrhythmias and weight loss.
If hypercalcemia persists for a long time, it can lead to kidney stones and kidney calcification and even an (irreversible) decline in kidney function.
Recommendation of the BfR
The BfR recommends: Anyone who wants to supplement vitamin D should use dietary supplements with up to 20 µg of vitamin D per daily dose.
According to the experts, with this dose the necessary vitamin D concentration in the body can be achieved without any exposure to the sun, without any health problems being expected.
Combination with vitamin K
High-dose vitamin D-containing dietary supplements are often combined with vitamin K, especially vitamin K2. The extent to which the interaction of these two vitamins affects health has not yet been sufficiently scientifically researched.
There is therefore not enough data for a reliable risk assessment of these combinations. The claim that vitamin K2 and high vitamin D intake reduce the risk of vascular calcification has not been scientifically proven.
For vitamin K, the BfR experts recommend adding no more than 80 micrograms (µg) of vitamin K1 or no more than 25 µg of vitamin K2 per daily dose to a dietary supplement.
People who take certain anticoagulants (coumarin-type anticoagulants), for example to prevent thrombosis, should generally only take vitamin K under medical supervision, as vitamin K can weaken the therapeutic effect of these drugs. (ad)