Unlike for other vital nutrients, we only cover part of our needs through vitamin D-containing foods such as salt-water fish or eggs.
Instead, we owe most of our body's reserves to the sun: when the sun's rays hit our skin, complex processes are set in motion, which ultimately produce vitamin D that can be used by the body. Vitamin D is therefore often referred to as a “sunshine vitamin”.
The role of vitamin D
Basically, vitamin D (cholecalciferol) is by definition not a vitamin at all, but a precursor of a hormone that must be converted into an active form with the help of UV light on the skin. Through many developmental steps, the skin cells, liver and kidneys are significantly involved in the formation of the active substance calcitriol.
Vitamin D is involved in countless regulatory processes in human cells and has a key function for our health:
Bone health:
Many people are familiar with vitamin D in the context of bone health. It ensures that the calcium absorbed through food is well absorbed and can be incorporated into the bones and teeth. Since it promotes the incorporation of calcium into the bone structure, it is also often referred to as an “incorporation aid”.
Muscles:
Vitamin D is also essential for normal muscle function and muscle strength. It supports muscle performance and regulates both the speed and coordination ability of our muscles – which is essential for walking safely.
Immune system:
The sunshine vitamin can also make a significant contribution to the function of the immune system. Nowadays, we know that vitamin D influences various properties of the specific as well as non-specific immune system.
In sufficient quantity, it can mobilize the body's defences and fight unwanted germs.
Age:
The body's ability to produce vitamin D itself actually decreases with increasing age. This is why older people often have particularly low vitamin D levels.
It is assumed that at the age of 70, only 25% of the body's own vitamin D synthesis capacity is still available.
Rule of thumb: If the shadow is longer than your height, you can assume that hardly any vitamin D is produced.
The skin type:
Skin type also depends on vitamin D production. Darker skin actually synthesizes less vitamin D than lighter skin. This is due to the higher melanin content of darker-skinned people, which absorbs more UV radiation.
Nutrition:
It is very difficult to make a significant contribution to our vitamin D requirements through our diet. This is because only a few foods contain relevant amounts of vitamin D.
To achieve the recommended daily requirement of 1,000 international units (I. U.), for example, 150 g of salmon or another fatty sea fish would have to be eaten every day - although vitamin D levels can vary.
Around 90 % of the requirement is covered by the skin's own synthesis. If sufficient vitamin D is not produced in this way for a variety of reasons, dietary supplements are a sensible alternative to regulate the vitamin D balance.