Vitamin D deficiency

Vitamin D is important for the formation of bones. It is also involved in metabolic processes and the formation of proteins. The vitamin is usually inadequately absorbed with food, the main source is sunlight: when it hits the surface of the skin, a biochemical process starts in the skin, at the end of which the body's own vitamin D production takes place.

Overview: What is a vitamin D deficiency?

Vitamins are substances that are important for health, but the human body can only produce them in insufficient quantities or not at all. They must therefore be taken in primarily through food. Strictly speaking, vitamin D is not really a vitamin at all, but a kind of hormone, because the body can produce it itself.

Nevertheless, despite this exceptional position, vitamin D is generally regarded as a vitamin. It supports the absorption of calcium and phosphate from the intestine and helps to incorporate these minerals into the bones. It is also involved in other metabolic processes and strengthens the muscles.

Vitamin D is a fat-soluble vitamin. Unlike water-soluble vitamins, which the body excretes in the urine, fat-soluble vitamins are stored in the liver, muscles and fatty tissue. Here they are available as a depot that the body can fall back on in the event of a shortage. However, the vitamin only accumulates if it is present in large quantities. However, this rarely happens with vitamin D. On the contrary: the majority of Swiss people are deficient in this vitamin, at least some of the time. The Federal Commission for Nutrition (FCN) assumes that there is a “widespread vitamin D deficiency” in Switzerland. As in many other countries, a large proportion of the population does not come into sufficient contact with sunlight through the skin to produce enough vitamin D.

Vitamin D is produced in the body in a complicated process involving the skin, liver and kidneys. This process starts when sunlight hits the surface of the skin – more precisely, the UVB radiation contained in the light. This is how the body usually produces more than 80 percent of the vitamin it needs; the rest of the vitamin D intake normally comes from food. Even with a healthy and balanced diet, it rarely contains sufficient amounts of vitamin D.

A noticeable lack of vitamin D occurs above all if the skin surface is exposed to the sun too rarely. This is the case, for example, if you spend most of your time indoors and only rarely outdoors. Or if your clothes cover so many parts of your body outdoors that your skin does not have the opportunity to come into contact with the UVB rays of sunlight.

Diagnosis: How is vitamin D deficiency diagnosed?

Vitamin D is the umbrella term for a group of vitamins called calciferols. These include vitamin D2 (also known as ergocalciferol) and vitamin D3 (cholecalciferol). If you are suspected of having a vitamin D deficiency, your doctor may suggest a blood test. The laboratory will then examine whether your blood contains enough vitamin D3 in stored form.

However, your doctor will first ask you about your lifestyle habits. If it turns out that you expose your skin to the sun often and long enough, a vitamin D deficiency is rather unlikely. However, if certain symptoms nevertheless indicate a vitamin D deficiency, this could also be due to impaired vitamin D metabolism. It can also be detected with the help of a blood test in the laboratory.

The value of a vitamin D precursor, known in medicine by the abbreviation 25(OH)D, is determined in the blood. The measured value can be displayed in nanograms (ng) per milliliter (ml). Depending on the result of the laboratory test, the following assessment is made:

  • Less than 10 ng per ml: severe vitamin D deficiency
  • 10 to 20 ng per ml: vitamin D deficiency
  • More than 20 ng per ml: acceptable vitamin D value
  • 30 to 50 ng per ml: desirable value
  • More than 50 ng per ml: risk of oversupply

An oversupply of vitamin D can lead to kidney stones or cardiac arrhythmia, among other things.

A low vitamin D level does not always have to be a cause for concern. It is quite normal for the amount of the vitamin in the blood to fluctuate. In the winter months, when there is little sunshine, vitamin D levels usually fall, whereas they rise in summer when there is intensive UVB radiation. The body can then store vitamin D in fatty tissue. Symptoms of deficiency do not appear in the short term, but only if vitamin D levels are significantly too low for a longer period of time. It is not possible to provide precise information on this because individual differences also play a role.

Symptoms: What are the consequences of vitamin D deficiency?

An extreme lack of vitamin D leads to rickets in children. When boys or girls develop this disease, their bones develop imperfectly. For example, the upper and lower legs do not harden sufficiently and bend. A severe vitamin D deficiency can also lead to bone softening in older people; doctors refer to this as osteomalacia.

Another possible form of bone damage occurs at an advanced age in the form of osteoporosis: This disease reduces the mass and fracture strength of the bones. As a result, the risk of fractures after a fall increases. A study (the “Zurich Hip Fracture Study”) has shown: Vitamin D deficiency was found in 80 percent of patients with a broken hip.

Another possible consequence of vitamin D deficiency is chronic kidney disease. This suffering can in turn lead to further illness. It is called “secondary hyperparathyroidism”. Its symptoms include muscle weakness, diarrhea and weight loss.

An increased susceptibility to infections, reduced muscle strength, muscle cramps and hair loss can also be consequences of a vitamin D deficiency.

Causes and risk factors: How does vitamin D deficiency develop?

The half-life of vitamin D is only three to six weeks. So if you spend time outdoors in the summer wearing light clothing and “soak up” plenty of sun to produce vitamin D, you can no longer benefit from this in the sunless winter. The reserves are then used up. However, many people do not even use the sunny season to replenish their vitamin D stores – out of concern that an excess of UV radiation could lead to skin cancer. In the sun, they protect themselves with sunscreen products that have a high or very high sun protection factor, which also prevents vitamin D formation.

Several groups of people are particularly at risk of vitamin D deficiency – due to a lack of exposure to sunlight, but also for other reasons:

  • Infants, because their sensitive skin must not be exposed to direct sunlight.
  • People with darker skin color, because the higher pigmentation of their skin naturally allows less UV rays to penetrate.
  • Chronically ill people, people in need of care and anyone else who can never or only very rarely spend time outdoors.
  • People who completely cover their bodies for religious or cultural reasons, so that neither face nor hands are exposed to sunlight.
  • Older people, because their production of vitamin D decreases.
  • People with certain diseases in which vitamin D metabolism is impaired, for example due to inadequate nutrient absorption in the intestine.
  • Patients who are taking a medication that has an adverse effect on vitamin D metabolism. These include certain antiepileptic drugs and cytostatics.

Therapy: How can vitamin D deficiency be treated?

After the connection between rickets and a lack of sunlight was recognized in the 19th century, special sanatoriums were established in Switzerland and other European countries: they offered extended “light cures” or “sun cures” to boost the body’s own production of vitamin D. Today, prolonged and unprotected exposure to the sun is no longer considered beneficial to health. On the contrary: UV radiation from the sun promotes the development of skin cancer.

Nevertheless, skin contact with sunlight is the easiest way to counteract a vitamin D deficiency. The following guideline applies to people with light to light brown skin (skin type I to skin type III) at our latitudes: To enable good vitamin D production, the face, hands and forearms should be exposed to the sun (even without sun cream) for around 10 minutes a day from June to August, and around twice as long in the other months. Sunburn should be avoided at all costs.

Another way to treat a vitamin D deficiency is to supplement your diet with the vitamin. It is usually administered in the form of drops or tablets. You should discuss the dosage with your doctor.

Prevention: How can vitamin D deficiency be prevented?

Relying on sunlight alone to produce enough vitamin D is often not enough. Especially not in winter. Between November and the end of April, it is often almost impossible to get a regular dose of vitamin D in Switzerland. Not even in the mountains, although the UVB radiation here is more intense than in the lowlands.

Although external conditions are better in the sunnier summer months, dermatologists recommend protecting uncovered areas of skin with sun cream during this time to reduce the risk of skin cancer. Even a low to medium sun protection factor (such as SPF15) blocks around 99 percent of UVB radiation.

Vitamin D accumulates in the fatty tissue of fish, especially in wild marine fish. If you eat a lot of high-fat salmon, herring, eel, mackerel or whitefish, you can cover at least part of your vitamin D requirement through your diet. However, in order to absorb all the vitamin D required for good health, you would have to eat large portions of fish almost every day.

As this is unrealistic, current guidelines recommend providing two risk groups in particular with external vitamin D: children (to prevent rickets) and adults over the age of 65 (to counteract the body’s own declining vitamin D production). For older people, a daily vitamin D intake of 600 to 1000 IU (international units) is sometimes given as a guideline. But the same applies here: ask your doctor beforehand.