Vitamin D is a special vitamin because, unlike other vitamins, it can be produced by your body itself. But whether you take it with food or your body produces it, vitamin D must always be activated by your body so that it can develop its effect. The active form of vitamin D plays an important role in your bone metabolism, your immune system and ensures that there is always enough phosphate and calcium in your blood. In this article you will learn how to keep your vitamin D level in balance and why this is especially important for people with kidney disease.
What is vitamin D actually?
Vitamin D, as the name suggests, is a vitamin. Vitamins are, as scientists often say, "essential". That sounds complicated, but it really just means that your body can't make them on its own. Which means you have to get them from your diet.
Together with vitamins E, K and A, vitamin D is a fat-soluble vitamin. Unlike the other fat-soluble and water-soluble vitamins, however, vitamin D has a special feature: your body can produce it itself.
As you have probably heard before, the sun plays a decisive role in vitamin D production in your body. This is perhaps a bit confusing, because we have just been talking about the fact that vitamin D - as an essential vitamin - must be ingested with food, since your body cannot produce it itself.
Now which of these is actually true? Is vitamin D really a real vitamin if our body can make it itself with the help of the sun's natural ultraviolet (UV) radiation?
Is vitamin D really a vitamin?
Although vitamin D is a vitamin, there are hardly any foods that contain much of it. Especially in plant foods, vitamin D is found only in very small amounts. Some foods that contain plenty of vitamin D are:
- Fatty fish (herring, mackerel, salmon, etc.).
- Egg yolk
- Edible mushrooms
- Cod liver oil (fish oil)
Unlike other vitamins, your body can also make vitamin D on its own. For one step of the body's own vitamin D production, the UV radiation contained in the sun is needed. Through intermediate steps in your liver and kidneys, these precursors are then converted into "active vitamin D." Only the active form of vitamin D can ultimately develop its full effect in your body. Since you only take in "inactive" precursors of vitamin D through your food, these also have to be activated by your body first. Although vitamin D is theoretically a vitamin, from a scientific point of view it is often referred to as a hormone.
How much vitamin D should I take in?
According to the German Nutrition Society (DGE), adolescents and adults in Germany generally consume between 2 and 4 µg (=micrograms) of vitamin D through food. However, a daily intake of 20 µg of vitamin D per day is recommended. The rest of the vitamin D production is covered by our own body. Isn't it fascinating what our body can do? Exactly how much vitamin D it can produce depends on several factors: our skin type, the latitude of where you live, the season, the time of day, the use of sunscreen, and the clothes you wear.
As you already know, the DGE advises a daily vitamin D intake of about 20 µg per day. The maximum recommended intake for healthy people is 25 µg of vitamin per day. This maximum amount of 25 µg vitamin D corresponds exactly to 1000 units (IU) vitamin D per day. In food supplements, the amount of vitamin D contained is often stated in IU. But what exactly does your body need this vitamin D for?
The role of vitamin D in the body
In our body, vitamin D performs a variety of functions. Its role in bone metabolism is particularly important. Together with parathyroid hormone, vitamin D regulates the calcium and phosphate balance and the formation, breakdown and remodeling of your bones. In this way, vitamin D ensures that your bones are strong and stable, and protects them from fractures. In addition, vitamin D is also responsible for:
- Increased absorption of calcium & phosphate by your kidneys.
- Increased absorption of calcium & phosphate via your intestines
- Increased mineralization of bones (strong bones)
- Better function of your immune system
Vitamin D deficiency can lead to a decrease in your bone strength (=osteomalacia), which makes you more susceptible to bone fractures. In children, it is mainly growth disorders and deformities of the bones that occur. This clinical picture in children is called rickets.
Vitamin D deficiency in chronic kidney disease
Chronic kidney disease often results in low levels of active vitamin D in your body. One reason for this is that the activation of vitamin D occurs in the kidneys. If they no longer function properly, this also leads to a lack of active vitamin D. However, vitamin D is not only activated in the kidneys, but also has an important task here: at the kidneys it regulates the excretion of calcium and phosphate, thus keeping these two minerals in balance.
As a result of a lack of active vitamin D, our body often lacks calcium. In response, the parathyroid glands in turn produce more parathyroid hormone. This parathyroid hormone commands your body to release calcium from the bones and pass it into the blood to compensate for the deficiency.
The result of the release of calcium from your bones can be bone pain or even bone fractures. So pay attention: keeping this interaction in balance is one of the most important jobs of you and your dialysis team! But don't worry, so that you know exactly how to keep your vitamin D level in a healthy range, let's take a detailed look at just that.
How do I cover my daily vitamin D requirements with kidney disease?
With kidney disease, your body often lacks active vitamin D despite sufficient sun and a suitable diet. Your doctor can detect this by low vitamin D levels in your blood. At the same time, the laboratory often shows elevated levels of parathyroid hormone and, of course, your doctors usually also look at your calcium and phosphate levels.
To support the therapy, active vitamin D can be prescribed, which can be taken as a tablet or in the form of drops. If this is the case, regular monitoring of laboratory values should be carried out to avoid over dosage. Optimally, the vitamin D level in the laboratory should be above 20 ng/mL or 50 nmol/L.
