Vitamin D is said to have numerous positive effects on health. Since it can only be formed in the skin under the influence of sunlight, one often hears the advice to take nutritional supplements with vitamin D in autumn and winter. Does this make sense?
There is no general answer to this question, writes the Federal Institute for Risk Assessment (BfR) in a current statement. Because the body can store vitamin D in fat and muscle tissue. Anyone who spends a lot of time outside in spring and summer and eats a balanced diet with fatty fish at least twice a week usually has sufficient vitamin D stores. According to the BfR, these people do not benefit if they take vitamin D as a dietary supplement: In studies, they were no less affected by cancer, type 2 diabetes, cardiovascular diseases and bone fractures as well as falls than people who did not take vitamin D -preparation received.
However, some people are particularly at risk for vitamin deficiency. These include people who spend little or no 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 risk group are older people because vitamin D production decreases significantly with age.
According to the BfR, anyone who wants to supplement vitamin D should use dietary supplements with up to 20 µg vitamin D (800 international units) per day. Even when taken long-term and taking other sources of vitamin D into account, this dose is not associated with any health-related effects. High-dose vitamin D preparations should only be taken under medical supervision. For example, in some clinical studies, daily administration of an additional 100 µg (4,000 IU) of vitamin D over a longer period of time showed 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 compared to the control group. At very high doses, vitamin D poisoning has also been observed, which required intensive medical treatment and in one case led to irreversible kidney damage requiring dialysis.
It is therefore best to determine your vitamin D status with a blood test by your doctor and to discuss whether additional intake makes sense and which dose is appropriate.