Vitamin D deficiency: when do tablets make sense?

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.

Consequences of a vitamin D deficiency

A severe vitamin D deficiency can lead to rickets in infants and young children. Bone softening (osteomalacia) can also occur in adults, as can bone fragility (osteoporosis).

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.

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.

What's important:

• 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.

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).

The daily requirement of vitamin D differs according to population group and is listed in the table (data in micrograms, µg).

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
• weakness
• fatigue
• headaches
• nausea
• vomiting
• disorientation
• 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.

Sources