Was ist Vitamin D3?

What is Vitamin D3?

The sun, which enables us to live on earth every day, is not only a life-giving source of heat and light, but also the supplier of an essential nutrient for our bone health: vitamin D3.

In this article we delve into the fascinating world of the “sunshine vitamin” and explore its crucial role in strong bones, an efficient immune system and our emotional balance.

What is Vitamin D3?

Vitamin D3, commonly referred to as “vitamin D” and scientifically referred to as cholecalciferol, is a subform of vitamin D that is naturally produced in the human body and plays a central role there. Vitamin D is just a general term for fat-soluble vitamins.

Vitamin D occurs in two forms in foods: as ergocalciferol (vitamin D2) in plant foods (e.g. chanterelles) and as cholecalciferol (vitamin D3) in animal foods (especially in fatty fish).

However, most of the vitamin D3 in our body does not come from food, but from somewhere else - the sun, at least indirectly. The sun does not provide us with immediately available vitamin D3, but ensures that it is synthesized in response to our skin's response to contact with the sun's UVB radiation.

And how exactly does that work?

The sun's UVB rays convert 7-dehydrocholesterol, which is found in our skin, into vitamin D3. After synthesis, vitamin D3 is transported to the liver, where it is converted into the active form, calcidiol.

A further conversion into the biologically active form, calcitriol, then takes place in the kidneys. Calcitriol regulates the calcium and phosphate balance in our body by increasing the absorption of calcium in the intestine and inhibiting the breakdown of bone tissue.

The biological function of vitamin D3 is closely linked to our calcium metabolism and our bone health. It also plays a role in muscle contraction and influences various cellular processes in our body.

Both endogenous synthesis through sun exposure and intake through foods and dietary supplements help maintain sufficient vitamin D3 levels in our organism.

Before we go into more detail about the individual biological functions of vitamin D3, we have summarized five (not so fun) fun facts about vitamin D3 to give you a foretaste of the integral importance of the sunshine vitamin.

5 (Not so) Fun Facts about Vitamin D3

  • Vitamin D deficiency worldwide: Despite its importance, vitamin D deficiency is widespread worldwide. This is due to various factors including inadequate sun exposure, certain diets and age-related skin changes.
  • Sunscreen and Synthesis: Wearing sunscreen reduces the production of vitamin D3 by blocking UVB rays. Nevertheless, protection against skin cancer is important, which requires us to carry out a balancing act.
  • Vitamin D3 and diabetes: There is evidence that inadequate vitamin D3 levels may influence the risk of diabetes. Studies show links between low vitamin D levels and an increased risk of diabetes.
  • Seasons Affect Synthesis: The amount of sunlight available varies with the seasons. In regions with limited sunlight, vitamin D3 supplementation may be necessary in winter.
  • Vitamin D3 is hardly contained in food: Vitamin D3 is only contained in a few foods - and in most foods only in small amounts. In addition, this vitamin is fat-soluble, so its efficient absorption in the intestine requires the presence of sufficient amounts of fat. People on low-fat diets or digestive disorders that affect fat absorption may therefore have additional difficulty meeting dietary vitamin D3 requirements.

What role does vitamin D3 play in our body?

Consequently, we would now like to take a closer look at the various biological functions of vitamin D3 for our overall health.

Vitamin D3 for Healthy Bones — The Key to Calcium Absorption

As already mentioned, vitamin D3 plays a key role in regulating the calcium and phosphate balance in the body. This mechanism is crucial for the mineralization of bones, which in turn supports their structure and strength. Vitamin D3 gives us our backbone, if you will.

A deficiency of vitamin D3 can lead to inadequate calcium absorption, increasing the risk of bone diseases such as osteoporosis. The way to strong bones is through the efficient absorption of calcium.

But how does vitamin D3 do this?

By stimulating calcium transport proteins in the intestine, vitamin D3 helps this essential mineral to be better absorbed and incorporated into the bones. It is not only important to consume enough calcium, but also to ensure that the body can utilize it optimally.

Vitamin D3 therefore acts, so to speak, as a key that opens the doors for calcium and thus lays the foundation for strong, resilient bones.

Vitamin D3 for muscles and coordination skills

Vitamin D3 also plays a central role in muscle function by regulating muscle contraction and their ability to coordinate. Studies have shown, for example, that people with low calcidiol blood levels fall more often than people with sufficient blood levels.

Vitamin D3 binds to muscle receptors, supporting strength development and helping to prevent muscle weakness. A sufficient vitamin D level is therefore crucial for the health and performance of our muscles.

Vitamin D3 to strengthen the immune system

But the effect of vitamin D3 is not just limited to our bones. It also acts as an invisible shield that strengthens our immune system.

Studies show that adequate vitamin D levels are associated with lower susceptibility to infections and inflammation. This protective mechanism ranges from warding off colds to more serious illnesses.

In times when our immune system is particularly challenged, it becomes clear how vitamin D3 acts as a natural amplifier that increases our body's resistance to disease.

Vitamin D3 to improve mood

The sun makes many of us feel like we're in a better mood - and that's scientifically proven. Vitamin D3 plays an important role in this effect.

Studies show that vitamin D3 plays a role in regulating neurotransmitters in the brain, particularly those related to mood. The happy mood in the sun could not only be due to the beautiful golden rays of the sun, but also to the vitamin D3 that is synthesized by them.

Conversely, a lack of vitamin D3 can lead to low levels of serotonin and dopamine, which in turn have been linked to mood problems such as depression.

This phenomenon has strong connotations with the so-called winter depression.

Sources of vitamin D3 – sun and dietary supplements

The crucial question now is: How can we ensure that we get enough vitamin D3?

The main source of vitamin D3 is the sun. When our skin is exposed to sunlight, the body begins to produce vitamin D3. However, factors such as skin type, season and geographical location are crucial for the synthesis, which is not possible for all of us at all times.

In Switzerland in particular, there is a long winter where the sun is sometimes not visible for a long time and sufficient synthesis of vitamin D3 through sunlight is hardly possible.

Vitamin D3 supplementation therefore makes a lot of sense in this country in order to ensure an adequate supply of this important vitamin.

Can't you get vitamin D3 through food?

As one of our “Fun Facts” already mentioned, vitamin D3 is only found in small amounts in our food. Many foods contain only traces of vitamin D3, especially if they are of plant origin, as the synthesis of this vitamin is closely linked to animal tissue.

Oily fish are the exception and are a fairly good source of vitamin D3, but these are not part of most people's everyday diet to adequately cover their needs.

For those who live in regions with little sun or who have difficulty spending enough time outdoors due to their work, dietary supplements can be a useful supplement.

Interestingly, the Yale School of Medicine has even announced that vitamin D3 from supplements is on a par with vitamin D3 synthesized from the sun.

And how should a good vitamin D3 supplement or nutritional supplement be designed?

Vitamin D3 Supplements – Quality is of integral importance

A high-quality and bioavailable vitamin D3 supplement should contain a form of cholecalciferol, the natural form of vitamin D3. It is also advantageous if vitamin D3 is offered with high-quality carrier oils such as fish oil to support fat solubility in the intestine. The combination of vitamin D3 and vitamin K2 (particularly in the form of menaquinone-7, also known as MK-7) is recommended because they have synergistic effects on bone metabolism and other physiological processes in the body.

Dosage should be based on individual needs and in accordance with the recommendations of healthcare providers.

We can conclude that vitamin D3 is not only the “sunshine vitamin” for strong bones, but also a crucial player for a functioning immune system, healthy muscles and a bright mood.

By consciously integrating sunlight and high-quality vitamin D3 nutritional supplements, we can ensure that our body optimally benefits from the benefits of this vital nutrient - in our latitudes all year round but especially in the winter months.

Please note that it is important to consult a professional before taking any dietary supplements or making any changes to your dietary habits. The information in this blog is for general educational purposes only and is not a substitute for professional medical advice.


  1. Institute of Medicine, Food and Nutrition Board. Dietary Reference Intakes for Calcium and Vitamin D. Washington, DC: National Academy Press, 2010.
  2. Norman AW, Henry HH. Vitamin D. In: Erdman JW, Macdonald IA, Zeisel SH, eds. Present Knowledge in Nutrition, 10th ed. Washington DC: Wiley-Blackwell, 2012.
  3. Holick MF, Binkley NC, Bischoff-Ferrari HA, Gordon CM, Hanley DA, Heaney RP, et al. Evaluation, treatment, and prevention of vitamin D deficiency: an Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab 2011;96:1911-30.
  4. Roseland JM, Phillips KM, Patterson KY, Pehrsson PR, Taylor CL. Vitamin D in foods: An evolution of knowledge. Pages 41-78 in Feldman D, Pike JW, Bouillon R, Giovannucci E, Goltzman D, Hewison M, eds. Vitamin D, Volume 2: Health, Disease and Therapeutics, Fourth Edition. Elsevier, 2018.
  5. Jones G. Vitamin D. In: Ross AC, Caballero B, Cousins ​​RJ, Tucker KL, Ziegler TR, eds. Modern Nutrition in Health and Disease, 11th ed. Philadelphia: Lippincott Williams & Wilkins, 2014.
  6. Borel P, Caillaud D, Cano NJ. Vitamin D bioavailability: State of the art. Crit Rev Food Sci Nutr 2015;55:1193-205.
  7. Silva MC, Furlanetto TW. Intestinal absorption of vitamin D: A systematic review. Nutr Rev 2018;76:60-76.
  8. Sempos CT, Heijboer AC, Bikle DD, Bollerslev J, Bouillon R, Brannon PM, et al. Vitamin D assays and the definition of hypovitaminosis D. Results from the First International Conference on Controversies in Vitamin D. Br J Clin Pharmacol 2018;84:2194-207.
  9. Okereke OI, Reynolds III CF, Mischoulon D, Chang G, Vyas CM, Cook NR, et al. Effect of long-term vitamin D3 supplementation vs placebo on risk of depression or clinically relevant depressive symptoms and on change in mood scores: A randomized clinical trial. JAMA 2020;324:471-80.
  10. LeFevre ML. Screening for vitamin deficiency in adults: US Preventive Services Task Force recommendation statement. Ann Intern Med 2015;162:133-40.
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