What is vitamin D and why it’s important
Vitamin D is actually a hormone that the body produces in the skin through the use of sunlight. This is why it’s also called the «sun vitamin».
Vitamin D performs the following functions in the body:
- It regulates calcium and phosphate metabolism.
- It promotes the absorption of calcium and phosphate in the intestine and thus ensures strong bones and teeth.
- According to recent findings, vitamin D is said to be important not only for the bones, but also for the entire musculoskeletal system, especially the muscles.
- A number of other positive properties are attributed to vitamin D: it is said to protect against cardiovascular diseases, autoimmune diseases and infections. However, recent research results cannot confirm these effects.
- It used to be said that vitamin D supplements help prevent osteoporosis, fractures and falls. But a recent large study analysis shows a different result: preventive therapies don't help healthy adults, i.e. those without risk factors. A benefit is only seen in patients who already have osteoporosis or fractures.
Symptoms of a vitamin D deficiency
Whether a mild vitamin D deficiency actually causes symptoms isn't clearly established. The symptoms mentioned aren't always considered conclusive.
Widespread bone and muscle pain
Preventing vitamin D deficiency: go outside regularly
80-90% of the vitamin D necessary for our health is formed in the skin. People who regularly spend time in the sun can at least ensure sufficient vitamin D formation from April to September.
- to expose your face and hands uncovered to sunlight for 5 to 25 minutes, several times a week. The duration depends on the skin type, the month and the time of day.
- Several short exposures to the sun are recommended.
- As a rule, everyday activities such as going to work or school or other periods spent outdoors are sufficient.
- Avoid sunburn, but don't use sun creams. These reduce vitamin D synthesis.
One cause of vitamin D deficiency in winter: not enough sun
In winter, sunlight in our latitudes isn't sufficient to produce enough vitamin D. However, the body can store it, which helps with the supply – provided you've spent enough time in the sun in the summer. Information varies on how long these stores remain filled and whether they are sufficient until spring.
What to remember in the colder months:
Eat a diet rich in vitamin D. The German Nutrition Society (DGE) recommends eating fatty sea fish once or twice a week.
Get out into the fresh air regularly even when it’s cold, preferably with your face and hands uncovered.
Seek advice from a doctor if you are in doubt, if you have symptoms and before resorting to vitamin supplements.
Getting vitamin D from food
Certain foods can supply a small amount of the much needed vitamin D. The following is a selection. (Vitamin D content in micrograms per 100 grams; values can vary greatly depending on the origin of the product).
||Vitamin D content|
||up to 25 µg|
||up to 25 µg|
||up to 6.25 µg|
||up to 6.25 µg|
whole hen’s egg
||up to 5 µg|
||up to 5 µg|
up to 1.25 µg
The daily requirement of vitamin D differs according to population group and is listed in the table (data in micrograms, µg).
Daily requirement of vitamin D
|Babies up to 1 year old||10 µg|
From the 2nd to the 60th year of life
Pregnant and breastfeeding women
From 60 years old
Vitamin D deficiency: values
A blood test will determine whether someone is suffering from a deficiency. This involves measuring the 25-hydroxyvitamin D (calcidiol) level. A concentration below 50 nanomoles per litre of blood serum (nmol/l) is defined by the Federal Office of Public Health (FOPH) as a vitamin D deficiency. A distinction is made between vitamin D deficiency (concentrations between 25-49 nmol/l) and severe vitamin D deficiency (below 25 nmol/l). If the level is below 25 nmol/l, vitamin D supplements are generally recommended as therapy.
Why not everyone needs a vitamin D test
Blood tests are only recommended for people with a higher risk of vitamin D deficiency and aren't generally recommended as preventive tests. They also make sense for older patients who have had a fall. The fact that the tests are now carried out on a large scale and as standard is controversial.
Who is at risk of vitamin D deficiency
- People with dark skin as they need more UV light.
- Old people: with increasing age, the body produces less vitamin D.
- Overweight people, presumably because of the greater absorption of vitamin D into fatty tissue.
- Pregnant women.
- Newborn babies. They are generally given vitamin D supplements in their first year to prevent rickets.
- People who wear full-body clothing for cultural/religious reasons.
- People who are housebound due to illness or in need of care and get little sun.
- Patients with chronic kidney failure or chronic liver disease.
Vitamin D supplements: capsules, tablets, drops
Vitamin D supplements should only be taken if a deficiency is detected and after consultation with a doctor, as an oversupply can be dangerous. It's not advisable to take more than 100 micrograms of vitamin D per day for a longer period of time. Vitamin D supplements are available in various forms such as capsules, tablets and drops.
Symptoms of too much vitamin D:
- heart arrhythmia
- a long-term overdose can also lead to kidney stones and kidney failure.
The body's own vitamin D production regulates itself, therefore an overdose from capsules is impossible. However, experts warn of the risks of randomly taking vitamin D from a range of sources – fortified foods, food supplements, medicines – at the same time.
Does vitamin D help fight COVID-19?
Some studies have found an association between higher levels of vitamin D and milder cases of COVID-19. However, this doesn't necessarily mean that vitamin D supplements have a positive effect on COVID infections. Whether or not vitamin D has a positive effect in preventing COVID is debatable – studies conducted so far come to very different conclusions.