Side Effects of Vitamin D: Questions and Answers

Nebenwirkungen von Vitamin D: Fragen und Antworten
The concept of vitamin D deficiency is well known, especially in the winter months: the body can only absorb vitamin D naturally from UVB rays, and the diet is not sufficient to cover the requirement. As a result, people often resort to dietary supplements to supply the body with the important vitamin for bone metabolism. In this article you will find out which vitamin D side effects are possible under which conditions in the human body.

the essentials in brief

  • Vitamin D strengthens the immune system, strengthens the muscles and boosts bone metabolism. The vitamin is mainly absorbed through the skin through sunlight.
  • Since vitamin D production via sunlight is problematic, especially in the winter months, vitamin D supplements offer a safe solution to always cover the need.
  • Side effects with vitamin D only occur with preparations. A constant overdose, as well as the lack of important cofactors, can have a problematic effect on the body.

What is vitamin D?

Vitamin D belongs to the group of fat-soluble vitamins and is also known as the “sunshine vitamin”. Unlike other vitamins, the body can produce vitamin D on the skin through exposure to UVB radiation from the sun. The cholesterol is converted into vitamin D3, which in turn is processed into vitamin D in the liver and kidneys.

What does my body need vitamin D for?

Vitamin D performs many functions in your body. The most important of these is its involvement in bone metabolism. This means that vitamin D promotes the absorption of calcium and phosphate from the intestine and also ensures its incorporation into the bones.(1) A supply of calcium is also essential for the muscles.(2) In addition, vitamin D is involved in other metabolic processes. In the hormonal system, it is responsible for the secretion of insulin and the functionality of the thyroid hormones.(3) Vitamin D also strengthens the immune system by boosting the defense against pathogens through a faster reaction time of the T cells.(4)

How do I recognize a vitamin D deficiency?

Symptoms of vitamin D are varied. Since vitamin D influences many processes, you will find deviations in bone health, muscles or the immune system in particular. A visit to the doctor will help you to be sure whether you actually have a vitamin D deficiency and need supplements. With the help of the blood test, your vitamin D content can be determined here. Here are some symptoms listed to preventively recognize a vitamin D deficiency:
  • hair loss
  • muscle weakness
  • disturbed bone mineralization
  • increased susceptibility to infection

Is it worth taking vitamin D supplements?

The vitamin D content in your body can easily be maintained by sufficient sunlight. Depending on where you live and the time of year, switching to vitamin D supplements can make sense for you if you don't get enough natural sunlight. Your vitamin D content can also be boosted with a tailored diet. However, there is not enough vitamin D in food to cover your needs holistically.
Foods that are particularly rich in vitamin D include fish, cheese, eggs and mushrooms.
Keep in mind that you can usually only cover 20 percent of your actual needs. Taking vitamin D supplements is particularly suitable for the following people:


Babies in particular should get plenty of vitamin D. The important vitamin protects babies from bone diseases and also strengthens the immune system, which prevents further diseases. A vitamin D deficiency is widespread in babies, as breastfeeding mothers with a vitamin D deficiency cannot fully cover the daily requirement of the child. In addition, coverage for non-breastfed babies is made even more difficult. Since babies are rarely exposed to blazing sunlight, preparations are useful here to maintain health.


Vitamin D deficiency is particularly widespread in the elderly age group. In addition, the effects of a vitamin D deficit are expressed here very strongly. In addition to osteoporosis and cardiovascular disease, the likelihood of depression and cognitive decline is also increasing. In order to reduce the health risk for people over the age of 60, it is therefore advisable to take vitamin D supplements here as well.

Dark-skinned people

Dark-skinned people also belong to the risk group, who often suffer from vitamin D deficiency. This is due to the higher melanin content, which means that the UVB radiation is shielded more.
yellow transparent tablets in a yellow light Vitamin D supplements can cover the daily requirement even without sunlight. With a constant overdose, however, side effects are possible here. (Source: / michele blackwell)
As a result, vitamin D3 is not built up on the skin as efficiently as in white-skinned people. Here, too, it is advisable to resort to dietary supplements.

What are the side effects of vitamin D?

With a normal intake of vitamin D you do not have to expect any side effects. However, there are special cases in which side effects can be expected when taking vitamin D. We will inform you about this in more detail here.

Vitamin D overdose

In addition to a lack of vitamin D, an overdose of it is also possible. This is usually extremely unlikely. You would need to exceed your daily requirement over 200 times over a period of several months.(5)


Actual vitamin D poisoning is simply impossible in a natural way, i.e. through exposure to sunlight and diet. This can only happen to you if you access vitamin D supplements and take too high a dose for several weeks. Individual cases occur when a vitamin D deficiency is overcorrected.(6)


Vitamin D overdoses are noticeable through symptoms such as nausea, vomiting, tiredness or even fever. These symptoms are caused by the increased calcium levels caused by vitamin D dosage. In acute cases, kidney damage and cardiac arrhythmias can even lead to death.(7)

lack of cofactors

Side effects of vitamin D due to a lack of important cofactors are also possible. The importance of vitamin K2 and magnesium is particularly noteworthy.

Vitamin K2 deficiency

Vitamin K2 is responsible for the removal and utilization of calcium. Accordingly, it is particularly important as a partner of vitamin D and it is advisable to take vitamin D in combination with K2, as they work synergistically. (8th) A lack of vitamin K2 can therefore lead to an accumulation of calcium in the tissues, even with correct vitamin D values, since the utilization is not optimal. This can become dangerous in the long run, since kidney stones, organ damage or calcification of the vessels are conceivable.(9) You can recognize a vitamin K2 deficiency by the following symptoms:
  • lack of concentration
  • fatigue
  • decreased blood clotting

magnesium deficiency

Conversely, vitamin D also promotes the absorption of magnesium in the intestine. That is why a magnesium deficit with a vitamin D deficiency is increasingly problematic. Even with vitamin D food preparations, the need for a magnesium deficiency cannot be adequately covered, since the utilization suffers as a result. Magnesium is needed for the body to convert vitamin D into its active form. As a result, it is also advisable to use synergies here and to exploit the interaction of the nutrients(10). That's why you should combine them if necessary. A lack of magnesium is manifested by symptoms such as:
  • fatigue
  • sleep disturbance
  • anxiety/nervousness
  • Headache
  • cramps
  • poor performance

What alternatives are there to vitamin D?

Vitamin D is essential for the human body and primarily supports the immune system and bone structure. However, vitamin D is completely natural for the body to obtain, so you don't necessarily need to resort to dietary supplements. Alternatively, you can exhaust that in the following way:
  • Sunbathing : Especially in summer you can use the UVB radiation to cover your vitamin D needs holistically. 30 minutes of sunlight daily are often sufficient to store reserves in the fatty tissue. Your body can fall back on these when there is no natural sunlight over the winter months. When sunbathing, however, you should make sure not to use any or weak sunscreen. Strong sun protection factors of over 20 block vitamin D absorption through the skin.
  • Food : You can also get vitamin D naturally through your diet. However, meeting vitamin D needs through diet is limited because sunlight is the main factor. The potential is exhausted for around 20% of the vitamin D requirement through food. Fatty fish are particularly rich in vitamin D.
filleted fish on a cutting board Fish are particularly rich in vitamin D. Nevertheless, you will not be able to cover the daily requirement of vitamin D even with daily consumption. (Source: /Jeremy Stewart)


Vitamin D is essential for the human body. It promotes bone preservation, strengthens the immune system and plays an important role in metabolic processes. Vitamin D deficiency is a widespread deficit, especially in the winter months due to the conditioned UVB radiation. Accordingly, it often makes sense to resort to dietary supplements, since intake through food is only possible to a limited extent.

You don't have to worry about side effects with vitamin D. These only occur from an overdose, and that is naturally impossible. Even with supplements, they only appear after you've abused them over a long period of time. In order to rule out other side effects caused by the lack of cofactors, it is advisable to combine vitamin D with the intake of K2 and magnesium. These nutrients work synergistically and supply the body holistically



  1. Vitamin D and Bone Health; potential mechanism
  2. Vitamin D and muscles
  3. Biology and Mechanisms of Action of the Vitamin D Hormone
  4. Vitamin D and the Immune System
  5. Vitamin D Toxicity-A Clinical Perspective
  6. Development of Vitamin D Toxicity from Overcorrection of Vitamin D Deficiency: A Review of Case Reports
  7. Vitamin D Toxicity in Adults: A Case Series from an Area with Endemic Hypovitaminosis D
  8. The Synergistic Interplay between Vitamins D and K for Bone and Cardiovascular Health: A Narrative Review
  9. Proper Calcium Use: Vitamin K2 as a Promoter of Bone and Cardiovascular Health
  10. Magnesium deficit? overlooked cause of low vitamin D status?
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