Kelly Turner
Vitamin D is responsible for much more than healthy bones. It is now known that almost every disease has a low vitamin D level. We explain how a good supply of vitamin D can be implemented, which foods contain vitamin D, which vitamin D preparations are recommended, how to assess sunscreen, and much more.
Vitamin D is absent in almost all diseases
For a long time it was believed that if your vitamin D level is too low, you risk rickets and osteoporosis, nothing more. However, we now know that low vitamin D levels are also associated with those diseases that are responsible for most of humanity’s suffering: cancer, cardiovascular diseases, diabetes, autoimmune diseases, depression, dementia, and chronic pain. It is therefore worth knowing more about the vitamin.
Vitamin D is a fat-soluble vitamin. In contrast to water-soluble vitamins, fat-soluble vitamins can be stored by the body, i.e. stored. Vitamin D is stored in fat and muscle tissue and in the liver. Thanks to these stores, the organism can – depending on how well the stores are filled – bridge a few weeks or even months without vitamin D intake.
Cholecalciferol and ergocalciferol: The two forms of vitamin D
Vitamin D comes in two main forms: vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol).
- cholecalciferol
Vitamin D3 (cholecalciferol) is found (usually in small amounts) in animal foods. However, it is also produced in the human skin from 7-dehydrocholesterol (precursor of cholesterol) under the influence of sunlight (UVB radiation).
- Ergocalciferol
Vitamin D2 (ergocalciferol) is found (usually in small amounts) in some plant-based foods. There it was created from ergosterol – also under the influence of UVB radiation. Vitamin D2 does not occur in the human body but can be converted into vitamin D3 (if it is ingested through foods containing vitamin D2).
UVB radiation is that part of the UV radiation that moves in a wave range between 290 and 315 nm, provides tanning and sun protection, but is also responsible for sunburn. The range of UVA radiation, on the other hand, extends from 315 to 380 nm. UVA radiation penetrates deeper into the skin than UVB radiation, causes less sunburn, but causes accelerated aging of the skin. Excessive exposure to the sun can promote skin cancer.
Which form of vitamin D is better?
Vitamin D3 is generally considered to be the “better” vitamin D, while vitamin D2 is not said to have such a good effect. Therefore, there are hardly any dietary supplements with vitamin D2 on the market.
However, a 2013 study found that consuming mushrooms that were exposed to sunlight and were therefore high in vitamin D2 (2,000 IU per 100g) increased vitamin D levels in humans just as well as it did taking the same amount of vitamin D2 and vitamin D3 supplements.
In addition, however, the researchers stated that mushrooms always contain certain amounts of vitamin D3, which of course could also have contributed to the positive study result.
Vegan vitamin D3 from lichen and mushrooms
Most vitamin D3 preparations are still made on the basis of lanolin (wool wax from sheep’s wool) and are therefore not vegan. In the meantime, however, there are also vegan, i.e. purely plant-based vitamin D3 preparations since vitamin D3 can also be found in lichens and – as explained above – some fungi, so these non-animal sources are now used for the production of vegan vitamins -D3 can use and discussions about “better” or “worse” vitamin D have become superfluous.
The lichen from which vitamin D can be produced is Cladonia rangiferina, also known as reindeer moss, so called because it is an important winter food source for reindeer.
This is how the vitamin works in the human body
How vitamin D works in the human body and in which forms and precursors it occurs there is explained in the following sections:
- bone vitamin and sun hormone
Vitamin D is also known under the terms bone vitamin or sunshine vitamin. As a bone vitamin because it is important for bone health, and as a sun vitamin because it can be produced by the body itself with the help of UV radiation. Sometimes you also read sun hormone, which is because vitamin D basically does not fall under the normal vitamin definition.
A vitamin is an essential substance. This means it must be obtained from food and cannot be made by the body itself. With vitamin D it is (ideally) the other way around. Most of the vitamin D requirements can be covered by self-production (= endogenous synthesis) with the help of the sun. Only a small portion is ingested through food. Because the vitamin D content of common foods is usually far too low you can hardly ever cover your needs with it.
Vitamin D is formed in every cell in the body
Up until a few years ago, people were of the opinion that the active form of the vitamin was formed with the help of sunlight exclusively with the help of the liver, kidneys, and skin.
Thanks to the American researcher Prof. Michael F. Holick, Professor of Medicine, Dermatology, Physiology and Biophysics and discoverer of the active form of vitamin D, we now know that apparently, every single cell in the body has the ability to produce active vitamin D form — another indication of how important the vitamin is.
This is how vitamin D is built up in the body
The active, i.e. effective, vitamin D3 is built up in the body in several steps:
Step 1: First, a vitamin D precursor is produced from cholesterol in the liver (7-dehydrocholesterol) and transported into the skin.
Step 2: Sun exposure to the skin produces prohormone or pre-vitamin D3 (cholecalciferol). The warmer the sun shines on the skin, the more vitamin D3 is formed – but only up to a certain value. An overdose of the vitamin through exposure to the sun is not possible due to this self-limiting mechanism.
Cholecalciferol is the form of vitamin D that you also take with dietary supplements, so it first has to be processed and activated in the body. If one were to take the active vitamin immediately, the danger of an overdose would be much greater. However, when ingesting cholecalciferol, the body can choose how much of it to activate.
Step 3: Vitamin D3 is now transported from the skin to the liver, where it is converted into calcidiol (= 25-OH-vitamin-D3 or also called 25-hydroxy-vitamin-D3). This form of vitamin D is stored in adipose tissue and also circulates in the blood.
Calcidiol is the form of vitamin D that is measured in vitamin D tests to determine vitamin D levels, but it is still not the active form of vitamin D.
Step 4: Calcidiol can now be converted into the active form of vitamin D. It is called Calcitriol or 1,25-OH-Vitamin-D or 1,25-Dihydroxy-Vitamin-D3. To control the calcium balance, this conversion takes place mainly in the kidneys, depending on the calcium level in the blood. But vitamin D not only controls the calcium balance.
The vitamin is known to have many other properties and effects. Therefore, calcidiol can also be converted into the active calcitriol by every single cell in the body when required – regardless of the calcium level.
Step 5: Calcitriol can now fulfill its vitamin D-typical tasks by docking to the vitamin D receptors of the cell nucleus the cell and thereby causing the cell to react in a wide variety of ways.
Vitamin D forms in the body: summary
All vitamin D forms of the vitamin D metabolism are summarized here once more:
Cholecalciferol is ingested through food or supplements or is made in the skin as a result of exposure to the sun.
Calcidiol (25-hydroxyvitamin D3) can be stored in adipose tissue or circulates in the blood and is measured in vitamin D tests.
Calcitriol (1,25-dihydroxyvitamin D3) is the active vitamin D3 that has an effect.
The vitamin in the vegan diet
It is often said that vegans (or vegetarians) belong to the risk group for vitamin D deficiency. After all, the vitamin is mainly contained in animal foods, so a deficiency in a vegan diet is inevitable.
Since the majority of the vitamin D requirement is covered by the body itself through its own production in the skin and the foods commonly used today contain far too little of the vitamin to cover the vitamin D requirement, the vitamin D supply is not dependent on diet, but mainly on how often you are in the sun, which can also be deduced from studies.
In a study from 2009, for example, the vitamin D status of 428 people was examined and no difference was found between vegetarians and normal eaters. However, what influenced participants’ nutritional status were frequency and intensity of sun exposure, degree of skin pigmentation (fair versus dark-skinned), and, of course, intake of vitamin D-containing supplements.
In fact, in 2013, a study (of a total of 176 Pakistani people between the ages of 20 and 80) found that non-vegetarians had lower levels of vitamin D than vegetarians, with slightly higher levels in both populations for those who did rural regions, while urban dwellers lived in lower regions.
In Germany, vitamin D deficiency is also so widespread that it cannot be associated with a specific diet. The Robert Koch Institute reports on its website as of January 25th, 2019 that according to the study on the health of adults in Germany (DEGS 1), more than half of the 6,995 participants aged between 18 and 79 years have an undersupply of the sun vitamin suffered. According to the study on the health of children and adolescents in Germany (KiGGS), more than 45 percent of the more than 10,000 children and adolescents examined between the ages of 1 and 17 had levels that were too low.
Vitamin D in dogs and cats
While humans have the ability to naturally produce vitamin D (endogenous synthesis), dogs and cats do not ( 1 ). You need to get the vitamin from the diet – either vitamin D3 from animal foods or vitamin D2 from plant foods, although only dogs can get both forms, cats most likely only vitamin D3.
Sunbathing is important
Since there have been warnings against sunbathing for years because of a possible risk of skin cancer, the increasing number of people affected by vitamin D deficiency is not particularly surprising. But now the question arises: which is better? Avoid the sun and no skin cancer, get a vitamin D deficiency? Or enjoy a healthy vitamin D level thanks to regular sun exposure, be spared from many diseases, but run an increased risk of skin cancer?
First of all, it is important to know that the development of skin cancer requires significantly more factors than sunbathing every now and then. From a holistic perspective, the risk factors for skin cancer include an antioxidant status that is too low, an imbalance in the intestinal flora, a weak immune system, hypersensitive skin, and also vitamin and/or mineral deficiency.
Since a study in 2016 showed that those who like sunbathing live longer, it makes much more sense to enjoy the sun than to risk a vitamin D deficiency. Apparently, sunbathing can even have such a positive effect that it can offset the negative effects of smoking.
Of course, as almost always, the same applies here: the dose makes the poison. Of course, you shouldn’t roast in the sun for hours every day. But regular, well-dosed sunbathing or – even better – outdoor sporting activities are recommended in any case.
So you can supply yourself with the sunshine vitamin
Sunbathing is therefore very suitable for supplying vitamin D. In general, if you were able to replenish your vitamin D stores in the summer, then your body will have enough stores for the winter.
Lose weight
However, this does not work in the case of obesity: vitamin D is stored in body fat but is often no longer released into the blood in the case of overweight. This is why overweight people often suffer from vitamin D deficiency.
Even a 10 percent weight gain can cause vitamin D levels to drop by more than 4 percent, which can be serious when levels are already low. If you are overweight, also lose weight for the sake of your vitamin D supply!
Tips for the right vitamin D supply in summer
In the summer months, i.e. from April to September, it is time to soak up the sun. But not too often and not too much. And so it is advised to sunbathe your arms and face for at least ten to fifteen minutes a day, although full-body sunbathing would of course be better.
However, dark-skinned people have to stay in the sun much longer than light-skinned people to get the same amount of sun vitamin, namely up to two hours. The evening sun is not of much use, as the sun should be relatively high so that the necessary UVB radiation also reaches the earth and thus your skin. Midday (12:00 – 3:00 p.m.) is therefore ideal for endogenous vitamin D formation.
However, it has been known since at least 2007 that there are still people who simply do not develop healthy vitamin D levels despite ample sun exposure ( 20 ). A study at the time was conducted with 93 young adults in Hawaii, who spent an average of almost 29 hours in the sun per week. Still, half of the participants had low levels (less than 30 ng/mL). The highest measured value in this group was 62 ng/ml, so the scientists suggested using this value as a limit for the vitamin D level to be achieved when using dietary supplements.
By the way: Glass is impermeable to the sun’s UV radiation. With the windows closed in the car or in the house, the skin cannot produce vitamin D.
Tips for the right vitamin D supply in winter
From October to March, the body lacks the sun to synthesize vitamin D with the help of UVB radiation. Even if the sun shines in winter, it is too low for sufficient UV radiation, with which the skin forms the precursor of the vitamin.
In winter, a healthy person, therefore, lives off the reserves in their fatty tissue. The longer the winter lasts, the sooner this supply dwindles. This is why flu waves may also occur mainly in February and March.
Only in regions south of the 41st/42nd At latitudes or in high mountains, the necessary UVB radiation can also be obtained in winter, so a winter holiday in the Mediterranean or in the mountains is a good idea.
If this is not possible and you are not sure whether your vitamin D stores will be sufficient over the winter, you can either have your levels tested regularly or at least take a preventive dietary supplement during the winter months.
So you can supply yourself with the sunshine vitamin
Sunbathing is therefore very suitable for supplying vitamin D. In general, if you were able to replenish your vitamin D stores in the summer, then your body will have enough stores for the winter.
Lose weight
However, this does not work in the case of obesity: vitamin D is stored in body fat but is often no longer released into the blood in the case of overweight. This is why overweight people often suffer from vitamin D deficiency.
Even a 10 percent weight gain can cause vitamin D levels to drop by more than 4 percent, which can be serious when levels are already low. If you are overweight, also lose weight for the sake of your vitamin D supply!
Tips for the right vitamin D supply in summer
In the summer months, i.e. from April to September, it is time to soak up the sun. But not too often and not too much. And so it is advised to sunbathe your arms and face for at least ten to fifteen minutes a day, although full-body sunbathing would of course be better.
However, dark-skinned people have to stay in the sun much longer than light-skinned people to get the same amount of sun vitamin, namely up to two hours. The evening sun is not of much use, as the sun should be relatively high so that the necessary UVB radiation also reaches the earth and thus your skin. Midday (12:00 – 3:00 p.m.) is therefore ideal for endogenous vitamin D formation.
However, it has been known since at least 2007 that there are still people who simply do not develop healthy vitamin D levels despite ample sun exposure ( 20 ). A study at the time was conducted with 93 young adults in Hawaii, who spent an average of almost 29 hours in the sun per week. Still, half of the participants had low levels (less than 30 ng/mL). The highest measured value in this group was 62 ng/ml, so the scientists suggested using this value as a limit for the vitamin D level to be achieved when using dietary supplements.
By the way: Glass is impermeable to the sun’s UV radiation. With the windows closed in the car or in the house, the skin cannot produce vitamin D.
Tips for the right vitamin D supply in winter
From October to March, the body lacks the sun to synthesize vitamin D with the help of UVB radiation. Even if the sun shines in winter, it is too low for sufficient UV radiation, with which the skin forms the precursor of the vitamin.
In winter, a healthy person, therefore, lives off the reserves in their fatty tissue. The longer the winter lasts, the sooner this supply dwindles. This is why flu waves may also occur mainly in February and March.
Only in regions south of the 41st/42nd At latitudes or in high mountains, the necessary UVB radiation can also be obtained in winter, so a winter holiday in the Mediterranean or in the mountains is a good idea.
If this is not possible and you are not sure whether your vitamin D stores will be sufficient over the winter, you can either have your levels tested regularly or at least take a preventive dietary supplement during the winter months.
