Vitamin D: What’s left of the hype surrounding the dietary supplement

Vitamin D is omnipresent: influencers and dietary supplement manufacturers promote the substance as a lifestyle and miracle cure. According to some advertising, there seems to be hardly any disease that vitamin D cannot protect against or cure. Many of these promises are not scientifically proven – and with some vitamin pills and drops it is easy to overdose and, in the worst case, poisoning. The most important questions and answers:

What exactly is vitamin D?

Vitamin D is also called the “sunshine vitamin”, and there is a good reason for that: our skin contains a precursor of the vital substance and can convert it into vitamin D with the help of ultraviolet sunlight. Because the body produces it itself, it is, strictly speaking, a hormone. However, the researchers who discovered vitamin D at the beginning of the 20th century and mistakenly classified it as the fourth vitamin known to date did not know this.

In addition to the body’s own production, vitamin D can also be absorbed through food, albeit in small amounts. Because only a few foods contain significant amounts, such as fatty fish and, to a lesser extent, egg yolk and liver.

Why do we need vitamin D?

Vitamin D promotes the absorption of minerals from food and is therefore essential for skeletal structure. A deficiency can lead to serious bone diseases: rickets in children and soft bones (osteomalacia) in adults. In addition, vitamin D is involved in immune defense and other metabolic processes: heart health, blood pressure and brain – they all benefit from good supply.

How common is a deficiency?

According to the Robert Koch Institute (RKI), vitamin D deficiency affects 12.5 percent of children and adolescents and 15.2 percent of adults in Germany. Another 40 percent are considered to have “suboptimal” care. However, the underlying data is based on a sample study that is more than ten years old, in which the vitamin levels in the blood serum of thousands of people were measured once. The significance of such laboratory data is limited: low values ​​do not prove a long-term deficiency and do not necessarily indicate health problems, according to the RKI. Because the vitamin D concentration in the blood fluctuates.

In our latitudes it is normal for the values ​​to go down over the winter. “We are a vitamin D-deficient country at this time of year,” says vitamin researcher Hans Konrad Biesalski, professor emeritus at the University of Hohenheim. Only between March and October do the sun’s rays have enough power to stimulate the skin’s production of vitamin D. Fortunately, our bodies are prepared for seasonal fluctuations. Liver and fat cells store vitamin D for later use. If you get enough sun during this time, your body can build up enough reserves for the winter months. But not everyone succeeds. To determine whether there is a deficiency, a blood test is needed. The 25-hydroxyvitamin D content (short: 25(OH)D) in the blood serum is determined. If it is consistently below 30 nanomoles per liter of serum, there is a deficiency. People with dark skin who are less able to produce vitamin D are at higher risk – as are older people, because the skin’s ability to produce vitamin D decreases over the years.

So are vitamin D pills or drops a must?

Not for most people. An important exception, however, are babies: direct sunbathing is out of the question for them, which is why infants should receive 400 to 500 international units (IU) of vitamin D every day until their second spring. That’s 10 to 12.5 micrograms.

For older children and adults, the German Nutrition Society (DGE) estimates the need to be 800 IU (20 micrograms) – but only if the body’s own production is lacking. Diana Rubin, board member of the German Society for Nutritional Medicine, complains that this addition is too often overlooked by the public. Instead, the impression prevails that everyone should take vitamin D, at least in winter, even without reason. “There was a huge hype that has continued unabated to this day,” criticizes Rubin. In fact, there are only a few people – such as those in bed-bound care – for whom the body’s own production stops completely due to a lack of sunlight. The doctor’s conclusion: “There is no need to take vitamin D regularly, unless there is a proven deficiency or osteoporosis.” In fact, vitamin D intake is an integral part of medical guidelines for bone disease.

Other experts are less strict when dealing with vitamin D in everyday life, especially in the winter months. “There’s nothing wrong with an intake of 800 units a day,” says nutritionist Biesalski: “This is ideal as a preventive measure, especially in old age.” Conclusion: According to current knowledge, this does not pose a risk to healthy people. However, it is unclear whether it will benefit you.

Does vitamin D intake protect against disease?

Books, advertisements and social media posts raise this hope, but the study does not support this. Numerous clinical studies have found no preventative benefit of vitamin D intake against cancer, cardiovascular disease, type 2 diabetes, incontinence, age-related macular degeneration, respiratory infections, depression and much more. There was also no positive effect on children’s growth, heart function or physical and mental performance. “A general recommendation for vitamin D supplementation to prevent illness cannot be justified based on the currently available scientific data,” writes the Federal Institute for Risk Assessment (BfR).

But what effect does the extra dose of vitamin D have when people are already sick? A number of studies have shown that diseases such as cancer, respiratory diseases and COVID-19 are regularly more severe when vitamin D levels are low. Is this also the reason for poorer chances of recovery? No, it’s not that simple. The connections have not yet been proven; a poor vitamin D supply could also be the result of previous illnesses or a symptom of an overall unhealthy lifestyle: Anyone who eats poorly and has little exercise in the fresh air is also exposed to vitamin D regardless of their intake -Reflects a higher risk of severe disease progression.

One thing is clear: a real vitamin D deficiency should always be compensated for. But even then not according to the motto: “A lot helps a lot”. The BfR even warns clearly about the risks of excessive intake, especially through high-dose dietary supplements.

What happens if you overdose on vitamin D?

Significantly increased intake over a longer period of time can be harmful and even life-threatening. The result of vitamin D poisoning is an increased calcium level in the blood (hypercalcemia), sometimes accompanied by nausea and abdominal cramps. In severe cases, according to the RKI, kidney damage, cardiac arrhythmias, loss of consciousness and death can occur. Due to these risks, the BfR recommends a maximum amount of 20 micrograms (800 IU) per daily dose for dietary supplements. However, many products from online shops, but also from drugstores and supermarkets, are more concentrated.

“I often see blood values ​​that are too high – almost always because the patients are taking nutritional supplements,” says Diana Rubin, who heads the nutrition team at Berlin’s Vivantes Clinic.

Why do experts warn against the Coimbra Protocol?

Some patients swear by high doses of vitamin D against multiple sclerosis and therefore take excessively high doses. The concept that became known as the “Coimbra Protocol” is spreading, especially on the Internet. But caution is advised. The concept, named after its inventor, the Brazilian doctor Cicero G. Coimbra, assumes that the cause of autoimmune diseases such as multiple sclerosis lies in vitamin D resistance, which can only be overcome by a (medically supervised) ultra-highly concentrated intake of at least 20,000 IU , sometimes up to 150,000 IU per day can be overcome. However, there is no evidence for this, or indeed for the benefit of supplementation in MS patients without vitamin D deficiency.

Instead, experts warn about the risks of approaches like the Coimbra Protocol. Just last year, the German Medical Association’s Drug Commission reported the case of a 65-year-old MS patient who developed acute kidney failure after taking 60,000 IU of vitamin D daily for six months. “The Coimbra Protocol plays no role whatsoever among serous physicians, in MS centers and MS outpatient clinics. On the contrary: we constantly actively warn our patients against high-dose vitamin D treatments,” says MS specialist Christoph Kleinschnitz, Director of Neurology at the University Hospital Essen. “Unfortunately, we have to do that because such therapeutic promises are very widespread in the patient community, especially via social media, and some black sheep among the doctors do the rest.” Kleinschnitz’s advice on the Coimbra Protocol: “Hands off.”