Vitamin D – What you need to know

Vitamin D deficiency is most prevalent in the winter. If your vitamin D levels are too low, this can manifest itself in symptoms such as fatigue and muscle weakness. Supplements can help.


The body produces vitamin D itself. Therefore, it is not really a vitamin, but rather a hormone. The most important forms are vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol).

Production and absorption of vitamin D

80–90% of vitamin D in the body is produced via the skin. Vitamin D3 is developed through UVB radiation. This travels in the blood to the liver and the kidneys, where it is converted into vitamin D (calcitriol). 20–30 minutes of exposure to the sun per day is normally sufficient to produce the vitamin D we need.

Sunscreens with an SPF of 20 and higher block the UVB rays and thus inhibit the production of vitamin D. The production of vitamin D in the body decreases in the winter as the sun shines for fewer hours and the UV radiation is not as intense.

Nutrition plays only a secondary role in the absorption of vitamin D, with the body getting 10–20% of its vitamin D from food. The main sources of vitamin D are foods of animal origin. Some plant-based products also have a high vitamin D content. To meet your daily requirement, however, you would need to eat large amounts of these foods, which is not very realistic. We will talk more about your daily requirement later on.

Foods rich in vitamin D include:

  • Eel
  • Herring
  • Trout
  • Salmon
  • Oysters
  • Tuna
  • Avocado
  • Porcini mushrooms
  • Eggs
  • Mushrooms

What does vitamin D do in the body?

Vitamin D promotes the absorption of calcium and phosphorous in the intestines. It therefore regulates the absorption of minerals and calcium levels in the blood. It also supports the development of the muscles, bones and teeth and strengthens the immune system.

Your daily requirement of vitamin D

Your daily requirement varies depending on age:

  • Infants up to age 1: 10 micrograms
  • People aged 1 to 60: 15 micrograms
  • People over age 60: 20 micrograms

15 micrograms of vitamin D are contained for example in 180 grams of wild salmon, 515 grams of raw chicken eggs (equivalent to approximately nine medium-sized eggs) or 485 grams of fresh porcini.

Vitamin D is stored for several months in the fat, muscles and liver. During the winter months, however, these stores are no longer sufficient. You can find out below which vitamin D supplements can help.

Vitamin D deficiency: symptoms and effects

A deficiency results primarily in the following symptoms:

  • Fatigue
  • Loss of appetite
  • Bone pain and muscle weakness
  • Sleep disorders

If vitamin D levels in the body are too low, calcium is depleted from the bones. This fosters osteoporosis. In other words, your bones become more brittle. In the case of serious deficiencies, in children this can lead to skeletal deformations, while in adults the bones soften, known as osteomalacia.

The demographic groups subject to an increased risk of vitamin D deficiencies include infants, children, pregnant women and breastfeeding mothers, the elderly, the chronically ill, and overweight and dark-skinned persons.

There are various factors that influence the production of vitamin D: latitude, time of year, weather, time spent outside, skin type, age and the use of sunscreen. Illnesses such as celiac disease (gluten intolerance) or Crohn’s disease (chronic bowel disease) disrupt the digestion and absorption of fats. This can impede the absorption of vitamin D in the intestines. Certain medications can also exacerbate deficiencies. Epilepsy drugs, for example, impair the metabolism of vitamin D by increasing the requirement for vitamin D or rendering the vitamin inactive.

A vitamin D deficiency is detected by means a blood test administered by your doctor.

What happens if you get too much Vitamin D?

Nutrition and sunshine cannot lead to an overdose. Only the excessive consumption of supplements can cause a spike in vitamin D levels. This results in an excessive concentration of calcium in the blood, which manifests itself in a general feeling of weakness, headache and cardiac arrhythmia. In serious cases, this leads to kidney stones and kidney failure and can even result in death.

Vitamin D supplements

Supplements containing vitamin D are available in a wide range of forms:

  • Tablets
  • Injections
  • Capsules
  • Drops
  • Enriched foods

There are the active ingredients vitamin D2, vitamin D3 and vegan vitamin D. Vitamin D2 is found primarily in plant-based products. Vitamin D3, in contrast, is a component of products of animal origin. Today, most supplements contain the active ingredient vitamin D3. Studies have shown that this is absorbed most easily by the body.

If the supplements do not contain any fat or oil, you should take them with a meal that is high in fats. This fosters absorption, since vitamin D is fat-soluble.


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