Vitamin D from the sun: the most important questions and answers

Vitamin D durch die Sonne: Die wichtigsten Fragen und Antworten

In order to prevent a vitamin D deficiency, it is important to go out in the sun regularly. The special thing about vitamin D is that our body can produce it itself under direct sunlight and can thus cover the majority of the vitamin D requirement.

In the following we will explain why sufficient vitamin D is so important for your body and why the sun is so important for the formation of vitamin D. You will also learn what to look out for when producing vitamin D and how you can use alternatives to producing your own vitamin D.

the essentials in brief

  • Vitamin is important for your body. It helps build bones and keep them healthy. A vitamin D deficiency can therefore have serious consequences for your health.
  • Our body can produce vitamin D itself when exposed to sunlight. We can cover about 90% of our vitamin D requirement in this way. We absorb the remaining 10% through our food.
  • In Germany, the sun's rays are only sufficient for vitamin D production between March and October. During this time, you should regularly expose your skin directly to the sun for a few minutes in order to build up enough vitamin D reserves.

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Vitamin D and sun: What you should know

The following is an overview of what you need to know about vitamin D and the connection between vitamin D and the sun. In addition, we will show you what you should pay attention to when developing vitamin D in the sun.

What is vitamin D and what does it do?

Vitamin D is a collective name for a group of fat-soluble vitamins. The most important of these are vitamin D2 and vitamin D3. These help with bone metabolism. They ensure that substances such as calcium and phosphate are absorbed in the intestine and built into the bones. This is probably the most well-known function of vitamin D.


Staying in the sun stimulates vitamin D production in the skin. (Image source: Dan Gold / unsplash)

In addition, vitamin D helps with other metabolic processes and with the formation of proteins, or the control of many genes. (1)

Why is vitamin D important for our body?

Vitamin D is often advertised as being a miracle cure for our bones. In a way, that's true. Vitamin D is responsible for ensuring that our bones are adequately supplied with calcium, phosphate and other important substances. These substances are essential to keep bones strong and healthy.

Especially during growth, it is important that sufficient vitamin D supplies the bones with all the necessary substances. This is the only way the bones can grow into the right shape and later complaints can be avoided.

But a supply of vitamin D is also very important for the maintenance of fully grown bones. This keeps the bones healthy and doesn't break easily. (2)

What happens with a vitamin D deficiency?

Vitamin D is essential for bones. A vitamin D deficiency can therefore have serious consequences for bone health. Decalcification and ultimately even softening of the bones can occur, which can lead to the following diseases:

Illness symptoms
rickets Impaired bone growth in children
osteomalacia Deformation of the bones due to decalcification
osteoporosis Decreased breaking strength of bones

For infants and growing children, this can lead to what is known as rickets. This means there are severe impairments in bone growth, which can lead to permanent damage and deformation of the skeleton. It can also lead to reduced muscle strength and an increased susceptibility to infections. (3)

Vitamin D deficiency can also have serious consequences in adults. Osteomalacia can often occur. This means that the decalcification of the bones can cause them to become deformed. In addition, bone pain, muscle weakness and reduced strength can be observed in this clinical picture.

Vitamin D deficiency can also contribute to osteoporosis, especially in older people. Here, the breaking strength of bones is reduced due to deteriorated bone tissue and reduced bone mass. (1)

Who is particularly at risk for vitamin D deficiency?

Some groups of people are particularly at risk for vitamin D deficiency. These primarily include people who spend a lot of time indoors and hardly move outside in the sun. This group mainly includes people who are unable to move much due to illness or disability.

Many people in need of care have problems getting out of the house on their own and are therefore particularly susceptible to vitamin C deficiency. (4.5)

People who spend a lot of time indoors or never expose their skin to direct sunlight are at risk.

People who obscure much of their skin, whether for cultural, religious, or medical reasons, can also become vitamin D deficient even when out in the sun. Vitamin D can only be formed by direct exposure to the skin. Any type of clothing or covering will prevent UV-B radiation from reaching the skin.

Older people are generally at risk for vitamin D deficiency. On the one hand, because they are usually not that mobile anymore and therefore don't go out in the sun much. On the other hand, the production of vitamin D in the skin decreases with age. (4)

Babies are also at risk of developing a vitamin D deficiency. It should be avoided to expose infants to direct sunlight, so they can only produce little vitamin D. (6)

Especially in our latitudes, dark-skinned people are at risk of vitamin D deficiency. This is due to the fact that the skin only lets through little UV radiation due to the higher pigmentation. The UV-B radiation in Germany is hardly intense enough to stimulate enough vitamin D formation. (7)

In addition, people suffering from chronic diseases of the stomach, intestines, liver or kidneys are at risk. Vitamin D metabolism is also inhibited when certain medications are taken. (8th)

What happens with a vitamin D overdose?

In addition to a vitamin D deficiency, vitamin D overdose can also occur. This is because vitamin D is stored in muscle and fat tissue. This can not only lead to an acute overdose, due to one-time excessive intake, but also to a gradual overdose.

This occurs when you take too much vitamin D over a long period of time and thus slowly build up an overdose. The body's own production normally does not lead to an overdose of vitamin D. (9)

Only the increased additional intake of certain foods, dietary supplements or a combination of both can become dangerous.

An overdose results in an increased calcium level in the body. This can lead to abdominal cramps, nausea, vomiting, or loss of appetite. In severe cases, it can even cause unconsciousness, kidney damage or cardiac arrhythmia. In the worst case, you can even die from an overdose. (10)

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  • Get an automatic 21% discount when you buy now 💸*

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How much vitamin D does my body need?

In order to recognize an overdose or a deficiency, there are some values ​​​​that prove a normal vitamin D level. To determine the vitamin D level, the concentration of 25(OH)D, a precursor of vitamin D, is measured in the blood serum. This concentration is given in ng/ml. Below are the values ​​and what they mean for your body:

Concentration of 25(OH)D in ng/ml Meaning
under 12 Lack of vitamin D supply, risk of diseases
12 - 20 Suboptimal care, negative consequences for bone health are possible
20 - 30 Adequate supply for bone health
30 - 50 Sufficient supply without additional health benefits
over 50 Possible oversupply with negative health consequences


Just over half of Germans have at least a slight vitamin D deficiency of less than 20 mg/ml. This deficiency is exacerbated in older people. In a study in Germany, three quarters of the women between the ages of 65 and 79 had a vitamin D value below 20 mg/ml even in the summer. (11)

How does the sun produce vitamin D?

The special feature of vitamin D is that people can not only consume it, but can produce it themselves. Vitamin D is formed in the skin when exposed to sunlight. For this, the skin must be exposed directly to sunlight.

The starting material for the formation of vitamin D is called 7-dehydrocholesterol. This substance is part of the cell membrane and is most present in our skin. Through a chemical reaction with the UV-B rays, previtamin D3 is first formed, which then becomes vitamin D through a further reaction.

The vitamin then travels through the blood to the liver with the help of certain proteins. There it is converted in such a way that it can be stored in the body over a longer period of time. (12.13)

In which months can vitamin D be formed by the sun in Germany?

In Germany, the sun's rays or UV-B radiation is not intense enough all year round to stimulate vitamin D formation. Vitamin D can only be formed all year round at latitudes below the 35th parallel.

However, Germany lies between the 47th and 55th degree of latitude. Here, UV-B radiation is only strong enough for the skin to produce vitamin D between March and October. (14)

clouds and sun

In our latitudes, the sun is strong enough for vitamin D formation from March to October. (Image source: chuttersnap/unsplash)

During this time, however, the body usually not only manages to cover its current needs, but also to build up reserves. As a result, in healthy people who spend enough time in the sun, the need for the winter months is covered as a reserve in the body.

How do I get enough vitamin D in winter?

As described above, in summer the body can produce and store enough vitamin D for the winter. However, it can happen that the body is not able to build up enough reserves for certain reasons.

Even if around 80 - 90% of the vitamin D requirement in healthy people is covered by the formation in the skin, around 10 - 20% comes from our food. You can therefore continue to meet your needs with a conscious, vitamin D-rich diet if you do not produce enough vitamin D yourself.

However, if you really do have a vitamin D deficiency, it is difficult to compensate for it through food. Most food contains little vitamin D and can therefore only be seen as a supplement to your own vitamin D formation. (15)

What time of day is best for vitamin D production?

Vitamin D is most produced when most of the UV-B radiation hits the earth. The steeper the sun is in the sky, the more intense or dense the UV radiation reaches us. The best time to produce vitamin D is around noon.

Depending on the season and thus the length of the day, the day offers more or less time to produce vitamin D.

Since production requires a certain intensity of UV-B radiation, only a few hours a day are suitable for this. When the sun is low on the horizon, not enough UV-B radiation reaches your skin.

Can vitamin D formation also be stimulated by indirect sunlight in the shade or through window panes?

Unfortunately, it is not enough for vitamin D formation to sit in a bright room, since UV-B radiation is disturbed by glass windows and vitamin D cannot therefore be formed in your skin. You can only make vitamin D indoors if you get direct sunlight on your skin through an open window.

You also produce less vitamin D in the shade. Even bad weather conditions, such as heavy clouds, can reduce vitamin D production by up to 90%.

Significantly less vitamin D is produced in bad weather.

Clothing also prevents the production of vitamin D. Since clothing casts a shadow on the skin, UV-B radiation cannot reach your skin unhindered.

For optimal vitamin D production, you should go outside in the sun on sunny days and at least expose your face and arms uncovered to direct sunlight for some time. (1)

What should you consider when vitamin D is formed by the sun?

For sufficient vitamin D formation, it is recommended to go out in the sun without sun protection at least two to three times a week between March and October. It is enough if your face, hands and arms are exposed to the sun. However, you should be careful not to stay in the sun for too long. Enough vitamin D is already formed in half the time in which you do not get sunburned without sun protection.

As a general rule of thumb, remember that you should expose parts of your skin to the sun for about 5-25 minutes each day for vitamin D production. The exact duration depends on your skin type. The more pigmented your skin is, the more sunlight it needs to produce enough vitamin D. (5)

Of course, you should definitely avoid sunburn to prevent an increased risk of cancer. So take care of your skin and don't stay in the sun for too long at a time. You can definitely make enough vitamin D without risking sunburn.

Here is an overview of the most important rules:

  • In the sun several days a week
  • Only a few minutes without sun protection
  • Avoid sunburn at all costs

What alternatives are there to vitamin D formation from the sun?

In addition to the body's natural production of vitamin D under sunlight, vitamin D can be obtained in the following other ways:

  • Diet: About 10-20% of our vitamin D needs are naturally covered by our diet. However, most foods contain very little vitamin D. Examples of vitamin D suppliers are: certain offal, sea fish, edible mushrooms and eggs.
  • Dietary supplements: If you suffer from a vitamin D deficiency, appropriate dietary supplements are an effective way to combat the deficiency. However, you should only resort to this remedy if your own production and natural nutrition are not sufficient, since in case of doubt an overdose can occur. (9)
  • Solarium: A visit to the solarium can also stimulate vitamin D production with a UV-B intensity like in midsummer. However, the UV-A radiation can be significantly higher here than it would be naturally. This leads to a significant risk of skin cancer, which definitely makes going to the solarium for vitamin D production not recommended.

Despite the alternatives, producing your own vitamin D in your body remains the healthiest and safest way to meet your vitamin D needs. This way you don't run the risk of getting an overdose of vitamin D and you don't stress your skin more than necessary by short stays in natural sunlight.


Your body needs vitamin D to build healthy bones and other important metabolic functions. A vitamin D deficiency is particularly dangerous in bone growth and can lead to malformations and severe pain.

Vitamin D is produced in the skin when exposed to sunlight. Therefore, between March and October you should regularly expose your skin to direct sunlight for short periods without sunscreen. This allows your body to build enough vitamin D reserves for the winter.

Avoid too much sun exposure on unprotected skin, a few minutes a day are enough for vitamin D production. Be careful with vitamin D supplements. Without an acute vitamin D deficiency and in connection with foods rich in vitamin D, an acute or gradual overdose can occur.


  1. Answers from the Robert Koch Institute to frequently asked questions about vitamin D
  2. Laird E, Ward M, McSorley E, Strain JJ, & Wallace J (2010). Vitamin D and bone health: potential mechanisms. Nutrients, 2(7), 693-724.
  3. Holick MF. Resurrection of vitamin D deficiency and rickets. J Clin Invest. 2006;116(8):2062-2072.
  4. Holick MF. Photosynthesis of vitamin D in the skin (1987): Effect of environmental and lifestyle variables. Fed Proc.
  5. Alfredsson L, Armstrong BK, Butterfield DA, et al. Insufficient Sun Exposure Has Become a Real Public Health Problem. Int J Environ Res Public Health. 2020;17(14):5014. Published 2020 Jul 13
  6. Kreiter, SR, Schwartz, RP, Kirkman Jr, HN, Charlton, PA, Calikoglu, AS, & Davenport, ML (2000). Nutritional rickets in African American breast-fed infants. The Journal of pediatrics, 137(2), 153-157.
  7. Richard, A., Rohrmann, S., & Quack Lötscher, KC (2017). Prevalence of Vitamin D Deficiency and Its Associations with Skin Color in Pregnant Women in the First Trimester in a Sample from Switzerland. Nutrients, 9(3), 260.
  8. Parva NR, Tadepalli S, Singh P, Qian A, Joshi R, Kandala H, Nookala VK, & Cheriyath P (2018). Prevalence of Vitamin D Deficiency and Associated Risk Factors in the US Population (2011-2012). Cureus, 10(6), e2741.
  9. Marcinowska-Suchowierska E, Kupisz-Urbańska M, Łukaszkiewicz J, Płudowski P, & Jones G (2018). Vitamin D Toxicity-A Clinical Perspective. Frontiers in Endocrinology, 9, 550.
  10. Koul PA, Ahmad SH, Ahmad F, Jan RA, Shah SU, & Khan UH (2011). Vitamin d toxicity in adults: a case series from an area with endemic hypovitaminosis d. Oman medical journal, 26(3), 201-204.
  11. Rabenberg, M., Scheidt-Nave, C., Busch, MA, Thamm, M., Rieckmann, N., Durazo-Arvizu, RA, ... & Mensink, GB (2018). Implications of standardization of serum 25-hydroxyvitamin D data for the evaluation of vitamin D status in Germany, including a temporal analysis. BMC Public Health, 18(1), 845.
  12. Webb AR, DeCosta BR, Holick MF. Sunlight regulates the cutaneous production of vitamin D3 by causing its photodegradation. J Clin Endocrinol Metab. 1989;68(5):882-887.
  13. Holick MF, Smith E, Pincus S. Skin as the site of vitamin D synthesis and target tissue for 1,25-dihydroxyvitamin D3. Use of calcitriol (1,25-dihydroxyvitamin D3) for treatment of psoriasis. Arch Dermatol. 1987;123(12):1677-1683a.
  14. Webb AR, Kline L, Holick MF. Influence of season and latitude on the cutaneous synthesis of vitamin D3: exposure to winter sunlight in Boston and Edmonton will not promote vitamin D3 synthesis in human skin. J Clin Endocrinol Metab. 1988;67(2):373-378.
  15. Holick MF, Binkley NC, Bischoff-Ferrari HA, et al. Evaluation, treatment, and prevention of vitamin D deficiency: an Endocrine Society clinical practice guideline [published correction appears in J Clin Endocrinol Metab. 2011 Dec;96(12):3908]. J Clin Endocrinol Metab. 2011;96(7):1911-1930.
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