Vitamin D is often in short supply in winter
From an early age, we have learnt that vitamins are important for our health. This includes the fat-soluble vitamin D. However, the term "vitamin" only applies to a limited extent in this particular case. Vitamins are essential micronutrients that are mainly absorbed through food. In the case of vitamin D, however, dietary intake only plays a subordinate role, as it is produced in the body itself with the help of UVB rays from the sun. It is therefore basically a hormone precursor, a so-called prohormone. The two most important forms of the vitamin are vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol).
Why is vitamin D so important?
Vitamin D3 is often referred to as the "bone vitamin", as it has a significant influence on bone metabolism and plays a key role in bone mineralisation. Vitamin D3 promotes the absorption of calcium and phosphate from the intestine and incorporates these into the bone structure.
However, this is by no means the end of vitamin D's work, as it has a wide range of tasks and is involved in our health in many ways. In addition to bone metabolism, it is also involved in the formation of proteins and the control of genes and influences our muscle strength. An adequate supply of vitamin D is also important for the immune system, a healthy nervous system, can prevent infections and generally supports the cardiovascular system.
According to the Robert Koch Institute, observational studies have also found links with vitamin D supply with regard to high blood pressure, type 2 diabetes and cardiovascular diseases [3] and cancer [1], but no causal evidence has yet been found.
How does the body absorb vitamin D?
If you want to be sufficiently supplied with vitamin D3, you should treat yourself to sunbathing more often in the summer months to avoid a vitamin D deficiency. 80 to 90 % of our vitamin requirements are covered by the skin, where the vitamin is produced by the body with the help of sunlight. Depending on skin type, season and time of day, five to 25 minutes is usually sufficient for vitamin D production. People with darker skin colour need to spend a little longer in the sun than others to get the same amount of vitamin D due to the stronger pigmentation of the skin. From April to September, you should get plenty of sun - always in moderation, of course - to boost vitamin D production. But be careful! Nevertheless, sun protection should not be neglected, as the sun's rays can be very aggressive, especially at midday in the summer months. This increases the risk of sunburn and skin cancer. In the evening and in winter, vitamin D can hardly be formed due to the lower UV-B radiation. To prevent vitamin D deficiency in winter, our body stores excess vitamin D3 in fatty tissue as a reserve for the winter months and thus keeps vitamin D levels at a relatively constant level.
What role does diet play in vitamin D intake?
Vitamin D can also be absorbed through food, but diet is not a decisive factor in the supply of vitamin D3. The vitamin is only found in a few foods, such as fatty sea fish, certain offal, edible mushrooms and eggs. However, the content of the vitamin in food is so low that the diet has no major influence and can neither prevent nor compensate for a vitamin D deficiency. It is also a misconception that people on a vegan diet are more frequently affected by a vitamin D deficiency.
Who is particularly at risk from a vitamin D deficiency?
Certain groups of people, such as infants, people in need of care and older people, are more frequently affected by a vitamin D deficiency than others. This is due to the fact that they spend less time outdoors and are therefore exposed to little or no UVB radiation, which is important for vitamin D production. Because their skin is still very sensitive, infants, for example, should not be in direct sunlight, while chronically ill and elderly people are usually hardly mobile and therefore spend little or no time outdoors. The same applies to people from cultures that cover large parts of their skin with clothing. They also have an increased need for vitamin D and are more susceptible to a deficiency of the vitamin.
People who suffer from chronic diseases of the stomach, liver or kidneys or who take medication that impairs vitamin D metabolism and can therefore favour vitamin D deficiency also belong to the risk group for vitamin D deficiency. These include, for example, anti-epileptic drugs or cytostatics. [2] These increase the breakdown of the vitamin by various enzymes in the liver and can disrupt bone metabolism, as they influence the processing of other micronutrients that have an effect on bones, such as vitamin K, calcium and zinc. When taking these medications, it is therefore often advisable to take a vitamin D supplement or a combination supplement.
In addition, weight gain also has an impact on vitamin D levels in the body. People who suffer from obesity are therefore particularly at risk of vitamin D deficiency, as it is no longer possible to transfer the vitamin into the bloodstream.
What are the symptoms of vitamin D deficiency?
If there is an undersupply, the low vitamin D level or vitamin D deficiency becomes noticeable through various symptoms. The first signs of an insufficient vitamin D supply are muscle and limb pain, muscle weakness and cramps, but hair loss, migraines and sensations such as numbness or tingling of the hands or lips can also be symptoms of a vitamin D deficiency. It is also generally known that people with a vitamin D deficiency are more susceptible to infections and are more frequently affected by cardiovascular problems (e.g. heart attack, stroke). [3] Other symptoms include frequent fatigue in everyday life, symptoms of weakness, mood swings and depression, sleep disorders and a weakened immune system.
In infants and young children, a vitamin D deficiency can lead to so-called vitamin D deficiency rickets. Rickets is a bone disease in which the bone substance is weakened. This means that the bones remain too soft during growth and become deformed. The curvature of the bones leads to symptoms such as bone pain and slower growth in affected children.
In adults, vitamin D deficiency over a longer period of time can lead to a condition known as osteomalacia. Osteomalacia is a decalcification of the skeletal bones, a disorder in the bone formation process in which minerals such as calcium are released from the bone substance. Similar to rickets, the bone structure becomes soft and deformation can occur. This is often accompanied by a weakening of the jawbone and an increased risk of periodontitis, a chronic disease of the periodontium. In the worst case scenario, a long-term vitamin D deficiency can also cause bone loss, or osteoporosis. Older people in particular are often affected by this. As vitamin D deficiency is often accompanied by muscle weakness and unstable posture, not only is the risk of falling particularly high in these people, but also the risk of bone fractures. But be careful! If you notice the symptoms of a deficiency, you should not simply take vitamin D supplements without consulting a doctor, but should first have a vitamin D status test carried out using blood tests. This is because, in addition to vitamin D deficiency, incorrect doses from supplements and excessive vitamin D levels can also harm the body.
Can an overdose of vitamin D3 harm the body?
The answer to this question is a resounding yes. While an overdose through sunbathing alone is hardly possible, you should be careful when taking vitamin D supplements. Too high a vitamin D level from taking a supplement can cause nausea, abdominal cramps and vomiting and can even lead to cardiac arrhythmia and kidney damage. As the vitamin is stored in the body's fatty tissue, an overdose can occur not only acutely but also gradually. In the long term, this can lead to poisoning (intoxication), which in the worst case can be life-threatening. Therefore, before taking a vitamin D supplement, you should always consult your GP first and discuss the correct dosage of the vitamin with them before taking it.
How much vitamin D does the body need?
The German Society for Nutrition (DGE) and the Robert Koch Institute give a daily vitamin D guideline of 10 µg for infants if vitamin D production cannot be covered by UV-B rays. [4] To counteract a vitamin D deficiency and to prevent rickets, infants are often given a preparation containing 12.5 µg of vitamin D3 in the first year of life. This makes it easy to compensate for low vitamin D levels. Adults should achieve a vitamin D level of 20 µg for an optimal vitamin D supply. The amount of vitamin is often not listed in micrograms (µg), but in international units (IU) for better comparability. 1 µg corresponds to 40 IU, which means that the recommended dose for adults is 800 IU of vitamin D.
If you want to avoid a vitamin D deficiency, you should therefore get enough sun in the summer months and build up vitamin D reserves, take vitamin D supplements under medical supervision if necessary or treat yourself to a holiday in the Mediterranean or in the mountains in the winter months, as the vitamin D requirement can also be met in winter thanks to the more intensive UVB radiation.
Stay healthy!
Sources
[1] https://www. zentrum-der-gesundheit.de/news/gesundheit/general-health/vitamin-d-deficiency-cancer
[2] https://www.deutsche-apotheker-zeitung.de/daz-az/2008/daz-45-2008/antiepileptika-und-vitamin-d
[3] https://www.zentrum-der-gesundheit.de/ernaehrung/vitamine/vitamin-d-uebersicht/vitamin-d-herz
[4] https://www.dge.de/wissenschaft/referenzwerte/vitamin-d/