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Vitamin D: Vital for health

Effect, deficiency, dosage, side effects, overdose

25 Mar 2022

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Vitamin D: Vital for health

What does the body need vitamin D for?

Contrary to what the name suggests, vitamin D is actually not a vitamin, but a hormone that the body can produce using sunlight. It is particularly important for building bones, teeth and joints and also involved in the following processes in the body:

  • Control the absorption of calcium in the intestines
  • Intact immune system and defense against infections
  • Synthesis of the body's own antibiotics
  • Build and maintain normal muscle function
  • Normal cell division
  • Reduction of inflammation in the body
  • Hormonal balance
  • Reduction of oxidative stress
  • Optimal signal transmission between the cells
  • Inner peace and better sleep
  • Adapted coping with stress
  • Mental performance function
  • Vitality and attention

Scientific studies have led to the assumption that vitamin D also plays a role in the prevention of a variety of diseases. This includes:

  • Autoimmune diseases
  • Colds
  • Osteoporosis and other bone diseases (including rickets)
  • Back and bone pain
  • Depressions
  • Diabetes
  • Cardiovascular diseases
  • High blood pressure
  • Chronic inflammation
  • Immune system disorders
  • Muscle weakness
  • Psoriasis
  • Joint rheumatism
  • Rheumatoid arthritis
  • Alzheimer's and neurological diseases
  • PMS
  • Cancer

Many people have a higher need for vitamin D, e.g. the elderly, children and also people who hardly spend time outdoors, who have dark skin tones or who are veiled. The health experts advise in these cases to use nutritional supplements. In England they go one step further: Now that many people are staying at home, the health authority in England is advising everyone to take additional vitamin D supplements every day. (Source:

How is vitamin D absorbed?

Vitamin D is the only vitamin that can not only be absorbed through the diet, but can also be produced by the body itself. Since vitamin D is only present in very small amounts in food, an adequate supply of the vitamin alone through food is extremely difficult. According to the German Nutrition Society (DGE), adolescents and adults in Germany only consume 10 to 20 percent of their daily needs with food - the body produces the majority of the vitamin using sunlight in the skin.

In the summer, 15 minutes of sunlight a day are enough for the body to produce the daily requirement of the vitamin. Even on cloudy days, UV radiation is usually sufficient to ensure adequate production. Nevertheless, studies have shown that up to 60 percent of people in Germany have insufficient vitamin D levels. The reasons for this are varied and are related to lifestyle, habitat or diseases that impair vitamin D intake. Several unfavorable factors can also come together and make an adequate supply of the vitamin difficult.

What happens if you have a vitamin D deficiency?

A vitamin D deficiency is particularly common in northern Europe in the winter months. One reason for this is that the majority of the population spends less time outdoors during that time than in the warm season. However, the low position of the sun between October and March in all areas north of the 40th parallel, e.g. north of Rome, prevents sufficient UV rays from reaching the skin even on regular walks. Although it is advisable to replenish the vitamin D depot in the summer months by spending a lot of time outdoors, the vitamin D level drops drastically after just a few weeks without sufficient vitamin intake.

Vitamin D deficiency: Symptoms

Low vitamin D levels are initially manifested by atypical symptoms such as fatigue and exhaustion, pessimism and depressed mood, listlessness, nervousness, easy excitability, sleep disorders, cravings for sweets or tooth decay and gum infections. In the further course, respiratory tract infections, an increased susceptibility to allergies or pain in the musculoskeletal system may occur.

Vitamin D deficiency means that calcium is no longer sufficiently stored in the bones and they become soft and flexible. If the vitamin D deficiency persists over a longer period of time, children's bones, particularly the skull and spine, may deform. In adults, a calcium deficiency can lead to a decrease in bone density, which favors the development of osteoporosis. Autoimmune diseases, loss of body functions, rheumatic complaints or personality changes can also be symptoms of a vitamin D deficiency.

Vitamin D levels: How much vitamin D does the body need?

The DGE recommends adolescents and adults between the ages of 15 and 65 to ingest 800 international units (IU) of vitamin D per day if the body can't produce vitamin D itself. This corresponds to around 20 micrograms of the vitamin. According to various vitamin D experts, however, this dose is only sufficient to meet the minimum requirements and to protect against vitamin deficiency diseases. In order to keep the vitamin D level constant at the required level, experts therefore advise adults with a body weight of 70 kg to take a daily dose of 5,000 IU on average.

Determine the individual need via a blood test

Babies, children, pregnant women and people with various diseases have different needs for vitamin D. In addition, many other factors play a role in the intake of vitamin D. This includes the age, body weight, skin color, intensity of sun exposure, lifestyle and absorption capacity of vitamin D and its metabolism. The recommended guidelines for calculating the optimal vitamin D dosage are therefore only indicative. A blood test is essential to find out how high your vitamin D level is.

Vitamin D supplements: does it make sense to take them?

Especially in the winter months, it is difficult to keep the vitamin D level constant at a sufficiently high level. Since the sun is not enough and the need for vitamin D can't be covered by the diet alone, taking vitamin D in the form of dietary supplements is recommended.

Who should take vitamin D tablets?

Taking vitamin D as a dietary supplement can be useful:

  • if you have a proven vitamin D deficiency
  • to maintain a normal level of vitamin D in the blood
  • to prevent osteoporosis (bone loss)
  • for the elderly for osteoporosis prophylaxis
  • for people with a tendency to depression
  • for children to prevent rickets
  • for people with high blood pressure
  • to prevent different types of cancer such as breast cancer, kidney cancer or colon cancer
  • to prevent and treat respiratory infections
  • to prevent autoimmune diseases

Vitamin D overdose

As with most substances, an overdose can also occur with vitamin D if the intake is very high. In this case, it is a vitamin D poisoning. For this, however, very high doses of the vitamin must be taken in the long term. Instead of the recommended 5,000 units daily, more than at least 10,000 IU, probably even up to 40,000 IU, of vitamin D would have to be added daily over a period of 3 months or longer to cause vitamin D poisoning. In order to avoid an overdose, it is advisable to have your individual needs checked with a doctor.

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Vitamin D dosage - This much is really necessary

Different organizations recommend varying doses of vitamin D. For example, in cases where vitamin D formation through sunlight is deficient, the DGE currently recommends a dose of 400 IU for infants up to 1 year of age and 800 IU for children, adolescents, adults, seniors, and pregnant and nursing women.

According to vitamin D experts this recommendation is too low and only represents the minimum daily intake required to stave off rickets.

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How to combine vitamin D and vitamin K properly

Recent studies clearly demonstrate that vitamin D3 and vitamin K2 are essential to good health. Deficiencies in both these vitamins are extremely common, which is why more and more people are taking vitamins D3 and K2 as a daily dietary supplement.

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How to determine the Vitamin D3 level

You can measure your vitamin D levels by using a blood test to determine if you have enough vitamin D in your body. In fact, not the active form of vitamin D is measured, but the concentration of 25(OH)D (25-hydroxyvitamin D) in the blood.

The 25 (OH)D value is a precursor of vitamin D, in which form is is transported in the blood. If necessary, this form is converted into the active form of vitamin D (calcitriol).

The 25 (OH)D value shows how much vitamin D you got through nutrition or produced during sun exposure. But this value does not tell you anything about your vitamin D levels throughout the year, which will vary depending on the sun exposure and vitamin D uptake from food.

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