Vitamin D is the only classic “vitamin” that the body can produce itself. The starting material is a molecule in the skin, the “fuel” for the synthesis is sunlight, or more precisely: UV-B radiation. This is not available at all times of the year in our and more northern latitudes. Passionate couch potatoes can develop a deficiency even in summer.
In addition, it makes a big difference whether a person has a light or dark complexion as to whether the vitamin D deficiency can really be remedied with a short walk. Fair-skinned people can achieve a healthy vitamin D level with comparatively little sunlight.
A current study, for which data from around 440,000 people in Great Britain were evaluated, has now revealed further relevant influences on vitamin D levels. The researchers at Trinity College Dublin responsible for this are now calling for the same recommendation to be abandoned for everyone. Their results show that the synthesis varies so much from person to person that a normal level cannot be assumed. Instead, in many cases you have to prescribe additional capsules and adapt the dosage to your individual needs.
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Until now, the rule was: healthy young people and adults should not have more than Take 20 micrograms (or 800 IU) of vitamin D per day in addition to food and sunlight. This is also what the German Medicines Commission recommends. A double dose is recommended for athletes and pregnant women because they consume more vitamin D. Other people have a slow metabolism that cannot produce enough vitamin D. By the age of 70, the ability to produce vitamin D is halved.
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For older people, we are therefore strongly advised to double the dose. Among other things, the vitamin influences bone metabolism and ensures firm, stable bones. If it is missing, it leads to “decalcification” and deformation; Children can develop severe rickets, and this condition also appears to promote diseases such as high blood pressure, diabetes, heart problems or cancer.
Obesity and cholesterol
And of course, dark-skinned people who live in regions with little sun have to make sure they get enough. There is no clear recommendation here, just the rule of thumb: the more pigments are stored in the skin, the less solar radiation gets through, and the greater the risk of developing a vitamin D deficiency. However, an overdose should be avoided because the substance is then not simply excreted but stored in the body.
What the researchers from Ireland have now discovered and published in the journal Clinical Nutrition makes it even more complicated. Apparently there are other, previously unknown physiological brakes on the body’s own production of vitamin D. An adult can be perfectly healthy, i.e. meet the Medicines Commission’s criteria for the standard dose, and still need more vitamin D – for example because they are overweight.
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This aspect came to light because the researchers also recorded the daily UV-B dose of their test subjects. Suddenly, study participants in the same age group had different vitamin D levels despite the same UV-B dose – the higher their body weight, the lower. Vitamin D tablets didn’t work as well for them either: they needed more to reach the same blood levels as comparatively slimmer people.
This seems plausible because vitamin D is one of the fat-soluble vitamins. “The effect is probably due to the fact that the substance is partially deposited in fatty tissue,” writes the first author of the study, health scientist Margaret Brennan.
There was also an inverse relationship with individual cholesterol levels: the more cholesterol, the less vitamin D. An effect that gave the researchers a headache. Vitamin D itself is part of cholesterol metabolism, in an indirect way.
According to Brennan, a substance called 7-dehydrocholesterol is, on the one hand, a precursor through which vitamin D is formed in the skin. On the other hand, cholesterol is also formed there from this molecule. Perhaps just when sunlight, which is supposed to stimulate vitamin D production, damages the cells; Cholesterol is needed to repair cell membranes.
Brennan believes the higher cholesterol levels could indicate a previously unknown underlying disease that is associated with an increased need for vitamin D. So far it is nothing more than a hypothesis. To truly understand the effect, further research is needed.
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However, medical practices should not wait for the results of these follow-up studies, but rather rethink now, says study leader Lina Zgaga, Professor of Epidemiology. Both high cholesterol levels and obesity are good reasons not to rely on general dosage recommendations, but rather to determine a patient’s vitamin D needs individually. And Zgaga emphasizes in a press release from her university: “When it comes to vitamin D, we need to move from a one-size-fits-all approach to personalized strategies. Our study underlines this.”