What is vitamin D and what is it needed for in the body
Strictly speaking, vitamin D, or cholecalciferol (vitamin D3), is not a vitamin because we can produce it ourselves. In fact, it is a prohormone, i.e. a preliminary stage of a hormone, which itself has no or hardly any hormonal effect, but must first be converted into its active form by the metabolism.
Cholecalciferol is produced in the skin and, with the help of co-factors, is converted into the active steroid hormone calcitriol, which has a variety of functions in the body. To tell the truth, science may not yet understand the full extent of the impact vitamin D has on the entire body. So far, over 2,000 genes have been discovered that are influenced by vitamin D.
Vitamin D3 is not found in plant-based foods. However, it can be found in fatty sea fish, eggs, or organ meat (e.g. liver, kidneys). This also explains why the peoples of the far north are not deficient in vitamin D, even though they see no sunlight at all for a relatively long time during winter, provided they eat accordingly. Their traditional diet with all sorts of sea creatures such as fish, seals, whales or mussels ensures a good supply of vitamin D (and other very valuable substances, which we will discuss in further articles). Some of you might remember being “tortured” with cod liver oil as a child (cod liver oil is only torture if it is of poor quality - then it becomes rancid and tastes disgusting - quality is key here).
Why we absolutely need vitamin D and why we don't produce it ourselves in winter
Vitamin D apparently has a very large influence on all kinds of processes in the body. I would like to highlight two areas in particular: the immune system and the psyche.
Studies show that if there are sufficient levels of vitamin D in the blood (we will go into this in another article), up to 1,200 genes that are directly related to the activity of the immune system are regulated by it. One part is activated, another part is deactivated. Think of it like a symphony orchestra with vitamin D as the conductor.
The influence on the psyche is also significant. We sure all know the winter blues. This is, among other things, due to the falling vitamin D level (full spectrum light itself also has an important influence) and many people who supplement vitamin D report a better mood during the winter months. But why supplement? You’ve probably heard from medical professionals that you only have to go into the sun for 10 minutes and that would cover your entire demand for vitamin D. Well, medical professionals may understand something about medicine, physics is obviously not their topic of expertise. The truth is that north of the 40th latitude, no UVB radiation penetrates down to the earth's surface in the winter months. Due to the low angle that the sun makes with earth in the winter half-year, UVB radiation is absorbed by the atmosphere and is therefore not available to us for the production of vitamin D.
Solariums are no remedy, because they produce UVA radiation almost exclusively.
The situation is not much better in summer
Even in summer, the reality for most people is that they are indoors at lunchtime or actually the whole day and therefore cannot produce any vitamin D. Studies have shown that a large part of the population already starts into the winter half-year with a vitamin D deficiency, during which the situation cannot improve “naturally”, as explained above.
Here one could at least assume one reason why older people have a poorer immune system and are generally more susceptible to infections. Many just don't stay outside in the sun for long enough. Of course, there are other influences to consider here.
But that applies in general. The body is a complex system. It depends on the perfect interplay of many nutrients and other factors such as exercise, light and a fulfilled life.
Vitamin D is therefore not a silver bullet, but it can make a valuable contribution on the way to better health.