Kidney stones were considered a possible complication of daily vitamin D supplement use. A new study refutes this assumption – and points to advantages.
Lynn Zimmermann / t-online
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Vitamin D is a vital substance. The body needs it for a strong immune system and to produce certain hormones. However, according to the Robert Koch Institute (RKI), only about half of all adults and adolescents have enough vitamin D.
This is why many people turn to vitamin D supplements, especially in the dark seasons. But critics point out the potential risks of an overdose when taking vitamin D regularly – especially if it is taken without a doctor’s prescription. Now a current study by the DKFZ has shown that this concern is unfounded. According to the experts, neither the feared risk of kidney stones nor atherosclerosis is increased by daily intake of vitamin D. The study was published in the journal Nutrients.
Vitamin D influences calcium balance
The reason for the warning about too much vitamin D is that it has a major influence on calcium metabolism. On the one hand, vitamin D causes the intestine to absorb more calcium and, on the other hand, the kidneys excrete less calcium. If you overdose on vitamin D, there is a risk of so-called hypercalcemia, i.e. an increased calcium level in the blood. In the worst case, this can result in kidney stones and hardening of the arteries (atherosclerosis).
To investigate how different amounts of vitamin D affect calcium levels, DKFZ researchers analyzed data from over 400,000 people. 4.3 percent of participants said they regularly take vitamin D supplements. Another 20.4 percent took multivitamin supplements that also contained vitamin D.
How much vitamin D do we need?
Theoretically, the body is able to produce enough vitamin D itself as long as the skin is exposed to sufficient sunlight. However, the RKI points out that vitamin D formation is mainly possible in this latitude from March to October. One way to improve vitamin D status is to take supplements.
However, the German Society for Nutrition has so far only recommended this for members of certain risk groups, such as older people or people with dark skin. The reference value for vitamin D intake is 20 micrograms per day, which corresponds to 800 international units (IU), if the body does not produce it naturally. This estimate, derived from studies by the DGE, applies to all age groups from one year of age. Infants under 12 months need 400 IU per day.
No kidney stones despite high calcium levels
The result was surprising: subjects who regularly took vitamin D had, on average, higher calcium levels. However, during the observation period of almost 13 years, they did not develop atherosclerosis or kidney stones more often than those who did not take vitamin D.
“This is the largest study in the world to date to examine the dose-response relationships between vitamin D supplementation and safety aspects of calcium metabolism. “Pleasingly, we were unable to determine any connection with diseases that can be traced back to an increased calcium concentration in the blood,” explained study author Dr. Ben Schöttker.
The authors therefore conclude that the high calcium levels were probably not caused by taking the vitamin supplements. They suspect other causes behind this symptom, such as hereditary factors. Another possibility: health-conscious people who regularly take vitamin D could also increasingly use calcium supplements.
Overdose only from 10,000 IU per day
According to first author Dr. Sha Sha, the study results show that taking vitamin D supplements can be considered safe. This is not surprising for her, as an overdose of vitamin D only occurs when “extremely high doses” are taken over a long period of time.
According to her, the usual vitamin D dosage in the EU is between 400 and 4,000 international units (IU) per day. Side effects of an overdose, on the other hand, are only observed in clinical studies from a daily dose of 10,000 IU, says Dr. Sha Sha.
On the contrary, the German Cancer Research Center points out that it was able to identify another important advantage in a summary of all meaningful clinical studies on vitamin D. As a result, taking vitamin D in tumor patients could reduce the risk of dying from cancer by twelve percent – provided the vitamin is taken daily.
“A vitamin D supplementation in moderate doses that is tailored to needs could make an important and very cost-effective contribution to the prevention of cancer deaths and various diseases,” adds co-author Prof. Hermann Brenner.
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