The effect of vitamin D3: the most important questions and answers

Die Wirkung von Vitamin D3: Die wichtigsten Fragen und Antworten

Vitamin D3 not only plays an important role in transporting calcium into the bones, because there is evidence that the effect of vitamin D3 can also help prevent other diseases.

This article is intended to show you what task vitamin D3 has in the body and what diseases it may have an effect on or whether it can even prevent them. We also go into the possibilities of vitamin D3 supplements. Our article is neutral reporting, we attach great importance to providing clarity with our article in relation to vitamin D3.

the essentials in brief

  • Some foods contain vitamin D3, but the greatest need is formed by synthesis in the skin from exposure to the sun
  • Vitamin D is an important player in bone metabolism. There is also evidence that a balanced vitamin D value reduces the risk of disease
  • For many people, supplementation is necessary to meet needs

Definition: What is Vitamin D3?

The vitamin D group includes a number of fat-soluble substances that are sometimes also called provitamins D. These provitamins include in particular ergocalciferol (vitamin D2 - this is the plant form) and cholecalciferol (vitamin D3 - the animal form). Some of them are metabolized by the body into calcitriol (the hormonal subform), the form responsible for most of vitamin D's effects. In this article we will use the term "vitamin D" by analogy with vitamin D3.

Vitamins is covered by food

A small portion of our vitamin D needs are met through food. (Image source: unsplash/Annie Spratt)

The body can naturally absorb vitamin D in two ways. It is either synthesized under the influence of UVB radiation from the sun, or provided by the diet.

A distinction is made between vitamin D2 and D3. Vitamin D2 is of plant origin, such as fungi, while vitamin D3 is of animal origin.

Vitamin D3 effect: What you should know

In addition to its bone metabolism, vitamin D has numerous other possible effects that have already been examined in numerous studies. In this section we have selected some interesting topics to give you a general idea of ​​the spectrum of action of vitamin D.

What effect does vitamin D3 have in the body?

Vitamin D is very important for the health of our bones and teeth. It plays an essential role in the metabolism of calcium in the body. It does this by regulating blood calcium levels by helping the intestines absorb this mineral while minimizing its excretion through the urine. It also participates in bone formation and helps bones absorb calcium.

The most well-known function of vitamin D is its involvement in bone metabolism. Among other things, vitamin D promotes the uptake (absorption) of calcium and phosphate from the intestines and their incorporation into the bones. It thus plays a key role in bone mineralization. (11)

Vitamin D is therefore essential for our health. Apart from that, vitamin D is also involved in other aspects of our body, some examples of which are presented here.

How does vitamin D affect the psyche?

An analysis brought together data from 13 studies involving more than 30,000 participants that found an association between low vitamin D levels and the risk of depression. The mean result showed that low vitamin D levels are indeed linked to depression, but here it could be a case of correlation rather than causation. (6)

In a 2016 study, among two groups of people who are depressed, one was treated with vitamin D supplements and the other with a placebo supplement. The aim of the study was to find out whether vitamin D can prevent depressive symptoms and anxiety. However, no effectiveness was observed here. (12)

Thus, there is no clear scientific evidence that vitamin D helps against depression.

How does vitamin D work against fatigue?

If you often feel tired in the winter, there is hope that vitamin D can help.

In 2016, a double-blind, placebo-controlled study of treating fatigue with vitamin D supplements was conducted. The study included 120 subjects who complained of fatigue but were otherwise healthy. The result of the study was that the group treated with vitamin D complained of less tiredness than the control group. (2)

How does vitamin D work against rickets?

Rickets is a disease that occurs in children due to vitamin D deficiency. Symptoms include a rash and a frog's belly.

Since infants must not be exposed to direct sunlight, vitamin D3 supplements are the best way to prevent rickets. The Federal Office for Radiation Protection recommends that infants and young children be given vitamin D supplements until the second early summer. (9)

How does vitamin D work against high blood pressure?

There is no precise proof of whether vitamin D is effective against high blood pressure. British researchers conducted an analysis of various studies to find out whether vitamin D can lower high blood pressure. However, only weak evidence of a slight effect could be found. (7) If you have blood pressure, it is important that you stick to the treatment plan prescribed by your doctor.

What effect does vitamin D have on the immune system?

A connection between the immune system and vitamin D is supported by scientific studies. One example is a study of the tuberculosis-causing agent Mycobacterium tuberculosis and vitamin D deficiency. The study provides evidence that low levels of vitamin D are associated with progressive tuberculosis infection. (1)

Another study examined whether vitamin D can build up a defense against an infection with influenza or whether an infection can be treated with it. The result shows that although there is no precise answer to these questions, the researchers do not rule out the importance of vitamin D in the fight against human flu. (10)

How quickly does vitamin D3 take effect?

If you plan on taking vitamin D supplements to counteract a deficiency, you won't feel any difference after a single dose.

In order for your body to recover and the value to normalize, the supplements must be taken regularly and over a period of weeks. You should definitely discuss the correct dosage with your doctor or pharmacist beforehand. After a few weeks it is possible that you will already feel a change.

How can you support the effects of vitamin D3?

In this chapter we explain how you can get vitamin D through sunbathing or through supplements. We give the most important information and the respective advantages and disadvantages. We also explore whether there are means that can possibly support the effect.


The easiest way to get vitamin D is from the sun. Preferably use your arms and legs for sun exposure, as the rather sensitive facial skin can only produce little vitamin D. It's also important to note that as we age, the ability of the skin to synthesize vitamin D decreases.

The RKI recommends exposing your face, hands and arms uncovered and without sunscreen to the sun two to three times a week between March and October. Dark-skinned people, such as those of African or South Asian descent, need to stay in the sun longer to produce the same amount of vitamin D than lighter-skinned people.

The Institute for Radiation Protection has published the following recommendation:

In the case of small children, children and adolescents, particular care must be taken to avoid high UV exposure and sunburn, because particularly in childhood and adolescence, strong UV exposure and sunburn increase the risk of later developing skin cancer. (9)

Healthy eating

In addition to the body's own synthesis, a small part of vitamin D is ingested through food. The following foods contain the richest amounts of vitamin D: oily fish such as salmon, mackerel, herring and sardines, as well as red meat and eggs. Certain vegetables, such as mushrooms, also contain vitamin D.

Groceries Vitamin D content per 100 g of food
herring 25
salmon (farmed) 5
mushrooms 2
avocado 5
whole milk 1.2
Camembert 1
beef liver 2
egg 2


The table shows that there are numerous foods that contain vitamin D3. Nevertheless, the need can only be met with difficulty through food alone.

Vitamin D3 supplements

The body's own vitamin D synthesis is often not sufficient to cover its own needs. This is particularly the case in the winter months in the latitudes north of Rome. It also affects people who are darker-skinned, or who are unable to expose their skin to the sun for health or religious reasons.

Many people also spend a lot of time indoors for professional reasons. In addition, infants are also supplied with vitamin D supplements, as they must not be exposed to the sun's rays to protect their skin.

Vitamin D3 capsule

Vitamin D3 supplements come in a variety of forms. (Image source: unsplash/Michele Blackwell)

It is suitable for these people to balance their vitamin D requirement with vitamin D3 supplements. D3 supplements are made from lanolin, which is derived from sheep's wool. So these are for people who are vegetarian, but not for those who eat vegan. However, for some time there have also been vitamin D3 supplements that are made from tree lichen and are therefore completely vegan.

Vitamin D from endogenous synthesis

To help you decide whether to take vitamin D with supplements or rely on the sun, we weighed the pros and cons of both methods. It is also advisable to determine the vitamin D level beforehand using a blood test.

In general, there are groups of people in whom the body's own vitamin D synthesis is impaired or not possible by solar radiation for various reasons. For these people there are alternatives in the form of food supplements.

Vitamin D from supplements

It is also a good idea to regulate the vitamin D balance with supplements. In the event of an acute deficiency, a healthy value can be achieved relatively quickly in this way.

The risk-benefit relationship between the risk of sun exposure without sunscreen and the time required for the body to synthesize vitamin D has not been clearly established, which may reinforce the argument for supplementation.

Weekly or monthly intake?

It is not necessary to take one pill every day to get adequate vitamin D levels. There are also products that allow for a weekly or even monthly dose. This is particularly recommended for seniors, who often take a large amount of medication every day.

Additional supplementation with vitamin K2

Even though many guidebooks state that vitamin D and vitamin K should only be administered together, otherwise the vessels could become calcified, there is no scientific evidence of any kind. On the one hand, there are almost no scientific studies on the relationship between vitamin D and vitamin K, and on the other hand there is no evidence that vitamin D calcifies the vessels without the addition of vitamin K. (4)


Vitamin D3 is synthesized in the body mainly through solar radiation in the skin and has various functions in the body. This is primarily the bone metabolism. However, different studies show that a balanced vitamin D value can have positive effects on fatigue, the psyche and the immune system. However, this was not the case with hypertension.

In the fight against rickets in babies and young children, vitamin D3 supplements are an indispensable tool. Furthermore, these are a good alternative for people who are unable to meet their vitamin D needs through exposure to the sun. In order to know the right dosage, the vitamin D value should be determined beforehand by a blood count in order to achieve the best possible effect.


  1. Nowak A, Boesch L, Andres E, et al. Effect of vitamin D3 on self-perceived fatigue: A double-blind randomized placebo-controlled trial [published correction appears in Medicine (Baltimore). 2017 Jan 20;96(3):e6038]. Medicine (Baltimore). 2016;95(52):e5353. doi:10.1097/MD.0000000000005353
  2. Davies PDO. A possible link between vitamin D deficiency and impaired host defense to Mycobac terium tuberculosis. tubercles. Elsevier 1985; 66(4):301-6.
  3. Haddad JG, Matsuoka LY, Hollis BW, Hu YZ, Wortsman J. Human plasma transport of vitamin D after its endogenous synthesis. J Clin Invest 1993;91:2552-5.
  4. Gröber, U., & Kisters, K. (2018). Vitamin D never without vitamin K2 - imperative or subjunctive? Empirical Medicine, 67(04), 226-230. doi:10.1055/a-0652-8337
  5. German pharmacist newspaper. (2019, August 21). Dekristol® 20,000 IU – off label and dangerous?
  6. Anglin RE, Samaan Z, Walter SD, McDonald SD. Vitamin D deficiency and depression in adults: systematic review and meta-analysis. Br J Psychiatry. 2013;202:100-107. doi:10.1192/bjp.bp.111.106666
  7. Witham, Miles Da; Nadir, M Adnanb; Struthers, Allan Db Effect of vitamin D on blood pressure: a systematic review and meta-analysis, Journal of Hypertension: October 2009 - Volume 27 - Issue 10 - p 1948-1954 doi: 10.1097/HJH.0b013e32832f075b
  8. Statement on products containing vitamin D (01/2016) Revision 1.1 (2017)
  9. Federal Office for Radiation Protection. Consented recommendation on UV radiation and vitamin D.
  10. Gruber-Bzura BM (2018). Vitamin D and Influenza Prevention or Therapy?. International journal of molecular sciences, 19(8), 2419.
  11. RKI - Gesundheit AZ - Answers from the Robert Koch Institute to frequently asked questions about vitamin D
  12. Choukri MA, Conner TS, Haszard JJ, Harper MJ, Houghton LA. Effect of vitamin D supplementation on depressive symptoms and psychological wellbeing in healthy adult women: a double-blind randomized controlled clinical trial. J Nutr Sci. 2018;7:e23. Published 2018 Aug 23. doi:10.1017/jns.2018.14
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