Vitamin D in old age - the sun vitamin

With a daily dose of sunlight, your body can produce a large proportion of what it needs itself: Vitamin D, the sun vitamin. Vitamin D is important for the calcium balance, for the bones and the body's defences. How much vitamin D does your body need, how is it absorbed and what is the vitamin D supply like in old age?

The term vitamin D, also called calciferol, refers to a group of different fat-soluble vitamins that are vital for our body. Vitamin D is necessary for the regulation of the calcium balance and the mineralisation of the bones. Vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol) are particularly important for us, although they are actually not vitamins at all, but a hormone precursor. The body can produce vitamin D itself with the help of sunlight and also absorb it from food.

Vitamin D plays an important role in bone health. It increases the absorption of calcium from the intestine into the bloodstream and reduces calcium excretion via the kidneys. Vitamin D promotes mineralisation, i.e. the incorporation of calcium and phosphate into the bones, so that they become stable and strong. It thus counteracts osteoporosis and prevents falls and bone fractures in old age. In young years, an optimal supply of vitamin D and calcium is particularly important, because the maximum bone density is built up until the age of about 25. The higher the bone density develops, the more favourable the effect on bone health.

Vitamin D has a positive influence on the muscles and is of great importance for athletes, but also for sarcopenia patients. Athletes benefit from improved muscle strength, an increase in maximum oxygen uptake, a reduction in muscle inflammation and overall improved athletic performance. In the treatment of age-related sarcopenia, i.e. the increasing loss of muscle mass and muscle strength with advancing age, the administration of high-dose vitamin D in combination with protein supplementation leads to measurable muscle growth.

Vitamin D occupies a special position among the vitamins, as it is absorbed through food, but can also be produced by humans themselves through exposure to sunlight. The body produces about 80 - 90 percent of the required vitamin D itself under the influence of sunlight; the body obtains the remaining 10 - 20 percent from food.

The body's own formation of vitamin D3 through the UV-B radiation of sunlight is also called endogenous synthesis. It depends on latitude, time of year and day, weather, skin type, clothing and length of time spent outdoors. In Germany, the following applies: anyone who exposes themselves to the sun for about 5 to 25 minutes a day with uncovered face, hands and parts of arms and legs during the months from March to October produces sufficient vitamin D3. Since the body can store the fat-soluble vitamin for several months in fat and muscle tissue and in the liver, there is also a vitamin D store for the winter months. Depending on the skin type, the amount of UV-B radiation absorbed varies: fair-skinned people absorb larger amounts of UV-B radiation compared to darker skin types and form a larger amount of vitamin D3 in the same period of time. However, they also have a shorter self-protection time of the skin and should only spend a short time in the sun without sun protection.

The diet contributes only insignificantly to the absorption of vitamin D. Vitamin D2 is found in some plant foods and mushrooms, but the content is low; only some mushrooms have a relevant vitamin D2 occurrence. Animal foods contain vitamin D3, high levels are found for example in fatty fish. The following table lists some foods with a high vitamin D content:

You can find the complete table here [1].

Vitamin D supply is measured by the serum 25-hydroxyvitamin D concentration, it includes endogenous synthesis and dietary vitamin D intake. A concentration of at least 50 nmol/l reflects a desirable vitamin D supply. In order to achieve this, the Deutsche Gesellschaft für Ernährung e. V. (DGE) gives an estimated value of 20 µg/day for children over one year and adults [2].

The diet with the usual foods provides approx. 2 - 4 µg/day and is not sufficient to reach the serum concentration. In the absence of endogenous synthesis, i.e. the body's own formation under the influence of solar radiation, the desired supply can be ensured by taking a vitamin D preparation.

If there is a vitamin D deficiency, not enough calcium can be stored in the bones, and the bones become soft and flexible. Adults suffer from bone softening (osteomalacia) Children suffer from rickets, in the course of which deformities of the skull, spine and legs also occur. Typical symptoms are muscle weakness and bone pain. The risk of osteoporosis also increases; the bones lose strength and break more easily.

Vitamin D deficiency increases susceptibility to infections and the risk of developing cancer, autoimmune diseases and cardiovascular problems. A severe course of respiratory diseases is often associated with a vitamin D deficiency.

Often a deficiency can be treated in a simple way, namely by spending time in the sun. If this is not possible, a vitamin D preparation can be useful. Your doctor will decide which dosage is advisable.

With increasing age, the skin's ability to synthesise vitamin D decreases; older people produce about four times less vitamin D naturally in the skin. While occasional sunbathing is sufficient to cover 80 to 100 % of the vitamin D requirement in young years, older people can only produce fractions of the required vitamin D in the skin despite frequent sun exposure. In addition, many older people do not spend much time in the sun due to lack of mobility, chronic illness or need for care. However, the need increases with age: bone experts demand that the vitamin D level in people over the age of 60 should be at least 60nmol/l to prevent osteoporosis. In fact, however, almost 60 % of 50-75 year olds in Germany have a lower vitamin D level.

The essential vitamin D supports the regulation of the calcium balance and serves to mineralise the bones. A deficiency can lead to osteomalacia and increases the risk of osteoporosis. If you spend about 20 minutes a day in the sun during the summer months, your body can generate 80 to 90 % of the vitamin D it needs at a young age. The remaining ten to twenty percent is taken in with food, with the generally low content still highest in fatty fish. Almost 60 percent of German seniors have vitamin D levels that are too low because the skin's ability to synthesise vitamin D decreases with age.