Vitamin D is necessary above all for the regulation of calcium balance and is therefore important for bone formation, blood clotting and the immune system. What cannot be synthesized in the skin under UVB irradiation, the body must absorb with food. We explain what forms of vitamin D there are and how you should use it and in what quantities.
Should I take vitamin D?
You should think about taking vitamin D if you belong to the group of people who rarely get to see sunlight. These include, in particular, elderly and bedridden patients who rarely leave the house, shift workers and anyone who is so involved in their job that they hardly have time for leisure activities.
Especially towards the end of winter, the vitamin D store in the fatty tissue is depleted and would be grateful for some support. However, a lot of fatty tissue should not mean that this would secure the vitamin D supply. On the contrary, in obesity the risk of vitamin D deficiency is even dramatically increased.
If in doubt, you should talk to your doctor about whether vitamin D therapy is appropriate and in what doses you should take vitamin D. If there is a medically justified suspicion of vitamin D deficiency, your doctor can perform a test and determine your blood level for vitamin D at the expense of your health insurance.
This is the case with osteoporosis, which mainly affects older people and, for hormonal reasons, mainly women. In children and adolescents, it is usually rickets, a vitamin D deficiency that leads to bone deformities and used to be the reason for prophylactic use of the unloved liver trans. Of course, you can also have such a test performed at your own expense as an IGeL service (individual health service).
Can I take vitamin D without asking my doctor?
Of course, even if a consultation is strongly advised. Because with an excess of vitamin D you do yourself no favor. As we have already seen, excess vitamin D is stored in fatty tissue. Water-soluble vitamins such as vitamin C can be taken as much as you like, what is too much is excreted by the kidneys (and leads to kidney stones if you overdo it). With fat-soluble vitamins (vitamin A, vitamin D, vitamin E, vitamin K) it is not quite so uncomplicated.
If too much vitamin D accumulates in fatty tissue, this can lead to hypervitaminosis or, in the worst case, to vitamin D poisoning. This manifests itself in increased blood values and urine values for calcium, hypercalcemia and hypercalcuria. This is because if sufficient amounts of calcium are not supplied with food at the same time, the large amount of vitamin D mobilizes calcium from the bones.
If you wanted to do your osteoporosis a favor by taking vitamin D, you achieve exactly the opposite. In addition, the high blood levels of calcium accelerate arteriosclerosis, lead in the worst case to heart attacks and strokes, and impair kidney function to the point of kidney failure. For such far-reaching complications, however, one must consume substantial amounts of vitamin D. Most recommended daily doses are in the range of 20-50 µg per day, and recommended blood levels are up to 100 ng/ml. This vitamin D value in the serum is not exceeded even by primitive peoples who are strongly exposed to the sun and are therefore always able to produce sufficient vitamin D. An overdose only leads to the aforementioned side effects from about 1,000 µg per day and blood levels above 150 ng/ml.
How much vitamin D should I take?
It depends on what your blood level shows for vitamin D. If you don’t want to go to your doctor with it, you can also buy a quick test at the pharmacy. For this, you will need to send a drop of blood from your fingertip in a tube to a lab that will do the analysis. If you know your blood level for vitamin D, you can use one of the now numerous vitamin D calculators on the Internet to work out your daily requirement.
In the formula screen, enter your body weight, current blood value, target value (30-60 ng/ml) and the number of days within which the target value should be reached. The program then calculates the necessary daily dose to reach the target value and the maintenance dose to maintain the value in the long term.
Nevertheless, you should take the calculated value only as a rough guide. No human being works like a machine and the vitamin D level in the blood depends on numerous factors. These include your age, how much vitamin D your intestines can absorb, how much is present in food and how much is formed in the skin, interactions with food and drugs, and many others.
What do I need to consider when taking vitamin D?
When you take vitamin D, there are a few things you need to keep in mind to make sure your vitamin D stores are replenished. This starts with taking the supplement: There should always be some fat in the diet, because vitamin D is fat-soluble and is best absorbed when it is dissolved in some fat in the intestines. It follows that it is best to take vitamin D supplements always combined with a meal.
Just a cup of black coffee in the morning and the vitamin D pill on an empty stomach won’t do any good at all. A little fat in the form of butter, margarine, cottage cheese or similar is recommended. Vegans can resort to a spoonful of vegetable oil for convenience.
Not only some fat plays a role in taking vitamin D. Likewise, you need to make sure that there is enough calcium, magnesium, vitamin C and vitamin K. Magnesium and vitamin C are needed by the liver and kidneys to produce active vitamin D, and vitamin K is involved in the incorporation of calcium into bones. If vitamin K is missing, calcium is not incorporated into the bones, but increases the risk of hardening of the arteries and thus heart attacks and strokes. Calcium and vitamin D are directly related.
Vitamin D promotes calcium absorption, which leads to the aforementioned problems in the absence of vitamin K. If there is not enough calcium when taking vitamin D, the vitamin D takes the calcium from the bone substance. By doing this, you are accomplishing the exact opposite of what you intended and promoting osteoporosis instead of combating it. If you regularly take blood thinners such as Marcumar or Warfarin, you must be aware that they interact with vitamin D, vitamin K and calcium. In such a case, it is better to ask your doctor how you should take additional vitamin D.
What kind of vitamin D supplements are available?
At present, there is much and extensive advertising for the “sun vitamin”. Accordingly, there is a whole range of different preparations on the market that are touted as dietary supplements. You can obtain vitamin D in the form of tablets, chewable tablets, capsules, soft capsules and in liquid form as drops. Some already have oils in them to improve absorption. Tablets are the cheapest, but contain numerous additives such as silicon dioxide and magnesium stearate.
Those who wish to avoid these should resort to capsules or drops. Most preparations contain vitamin D3 as the active ingredient, and some also contain vitamin D2 in addition. Since the latter must first be converted into vitamin D3, it is increasingly rare to find. Mostly vitamin D3 from wool fat (Adeps lanae) is used, vegan vitamin D3 is obtained from lichen. Under certain circumstances, an addition of vitamin K is useful for the reasons described above.
In cases of clinically manifest vitamin D deficiency in the form of osteoporosis, physicians usually prescribe Dekristol 20,000 IU, which is available by prescription and which patients should take every one to two weeks. For most patients, this is easier than taking it daily. Even though no overdose is to be expected when used properly, one should have the vitamin D level in the blood checked from time to time.
The forms of vitamin D
Strictly speaking, vitamin D is not a vitamin at all, but a hormone. There are historical reasons for this designation. Actually, vitamins are, according to the word, vitamin elements that the body needs in only small quantities, but is not able to produce itself.
This does not quite apply to vitamin D, because humans can not only take it in with food, but also synthesize it themselves. Actually, all animals do this – with the exception of the guinea pig, which also depends on vitamin D in its diet. Self-synthesis even exceeds normal dietary intake, but is often insufficient to meet daily needs.
This has a lot to do with the fact that prehistoric man left sunny Africa and had much less sunlight available in his new areas of settlement. This is one of the reasons why the rare mutation to white skin color has prevailed among Asians and Caucasians: Light skin is much better able to synthesize vitamin D than darkly pigmented skin.
Basically, one must distinguish between plant and animal/human vitamin D. The D vitamins are generally referred to as calciferols (from the Latin calx, lime, and ferre, to carry) because of their importance for calcium balance. Each organism synthesizes them from its own sterols (sterols): plants from ergosterol (ergosterol), animals and humans from cholesterol (cholesterol). Accordingly, the form found in plants is called ergocalciferol or vitamin D2, and that found in animals and humans is called cholecalciferol, calciol, or vitamin D3.
A human can only take a small amount of vitamin D by ingesting it with normal food. Only about 5-20% of the daily requirement can be met in this way. The body synthesizes most of it itself in the skin. The basic substance for this is cholesterol, which the liver converts into 7-dehydrocholesterol. This reaches the skin with the blood, where it is converted into provitamin D3 under UVB irradiation (290-319 nm wavelength). Since this is thermodynamically unstable, it isomerizes to vitamin D3 by body heat.
Bound to the vitamin D-binding protein (DBP), the cholesterol thus converted returns to the liver via the bloodstream. The liver hydroxylates the cholecalciferol with the help of vitamin C to 25-hydroxy vitamin D3 (calcidiol), which functions primarily as a vitamin D store and serves to transport it in the bloodstream. The body can store an excess of vitamin D in the form of calcidiol in fatty tissue and retrieve it when needed. The actual bioactive form of vitamin D is its doubly hydroxylated form 1,25-hydroxyvitamin D3 (calcitriol), which the kidneys produce from calcidiol with the participation of vitamin C and magnesium.
Calcitriol acts like a hormone. Similar to the closely related steroid hormones (such as the sex hormones testosterone and estrogen), it binds in the cell to special receptors (vitamin D receptors), which channel it into the cell nucleus, where it initiates the reading of certain genes and the biosynthesis of various proteins.
One word in conclusion
Also, when taking vitamin D, as with all supplements, you should keep in mind that if you lead an unhealthy lifestyle, all vitamins, superfoods and trace elements are of no use.
Therefore, you should maintain a healthy lifestyle, exercise a lot, eat healthy and refrain from smoking and excess alcohol. You don’t have to put out a fire that you don’t start. This is especially true for vitamin supplements. And especially with vitamin D, plenty of light and sun are the best vitamin D sources of all. You never have to count on that either: With sunlight, it is never possible to overdose on vitamin D, because the body regulates synthesis and consumption all by itself.