Vitamin D and K - a strong team

Long working days, little time outdoors and then maybe even winter. The problem: Too little sunlight also means too little vitamin D for the body. This is because 80 to 90 percent of vitamin D is produced by UV-B rays through the skin. But especially in the dark season from October to March, the sun's rays are often insufficient. As a result, around 50 percent of the population is undersupplied with vitamin D. This is the reason why the sun's rays are often insufficient. In an expert interview, nutrition researcher Prof. Dr. Tilman Grune answers our questions about "sun vitamin D" and his important partner - vitamin K.

What does the sun have to do with vitamin D?

A vitamin is normally a substance that cannot be synthesized by the body and has key metabolic functions. Vitamin D is an exception: we can synthesize vitamin D, but only when exposed to sunlight. Precise UV-B radiation. This is the intensive part of sunlight that can also cause skin cancer.

So what makes vitamin D a vitamin?

In northern latitudes, we usually do not have enough sunlight to synthesise enough vitamin D. This is why we have to take into account the fact that we do not have enough sunlight. This has been known for about 100 years, and vitamin D also protects against rickets, the classic vitamin D deficiency disease. Sun exposure should be about 15 to 30 minutes per day for about a quarter of the body's surface. Then there are other factors that influence vitamin D synthesis. These include sun protection, skin type and age. Since this exposure to the sun is almost always insufficient, vitamin D must be continuously ingested with food.

If I get enough sun in the summer, do I have enough vitamin D reserves for the winter?

Vitamin D is a fat-soluble vitamin and can be stored as such. This happens in the liver, fatty tissue and muscles. These stores can contribute to the supply of vitamin D during the sunny months. However, a sole supply of vitamin D from filled stores is not sufficient for the dark season and must be supplemented with food.

Why does my body need vitamin D?

In short: to stay healthy. It is known that vitamin D acts in the bone metabolism and ensures the absorption of calcium into the organism. Calcium is a major component of solid mineral bone. Vitamin D improves the absorption of calcium in the intestines and keeps it in the body. At the same time, vitamin D has a positive effect on bone cells. This is the classic function of vitamin D; a vitamin D deficiency in this area leads to rickets, a deformation of the skeleton. In recent years we have gained a lot of experience in this field. Today we know that vitamin D assumes functions in the immune system, in muscle metabolism and in cell division.

Can the daily requirement of vitamin D be covered by the diet? What influences the individual vitamin D balance?

Essentially three factors: food, exposure to the sun and the body itself. In the latter case it is skin pigmentation: the darker, the worse the vitamin D synthesis in the sun. The aging skin also has a lower synthesis performance. Another point: the higher the body fat content, the more vitamin D you need. We have already talked about sun exposure. It should be borne in mind here that many professional activities no longer take place outdoors - from the factory to sales to the office. In addition, our leisure activities have often shifted indoors: computers, television; even sports take place in the fitness center. We can influence our vitamin D supply sustainably through nutrition. The best way to do this is through fresh sea fish. This requires approx. 100 to 200 g - every day. Honestly, who really eats like this? Other sources are relatively high-fat animal products such as milk fat (butter), cheese, eggs and liver. But they only contain tiny amounts, so you will never achieve such an optimal intake. Other food components can improve the vitamin D effect. Here, a sufficient calcium intake and vitamin K must be called will be. By the way, the classic vitamin D - also known as vitamin D₃ - is of animal origin. From plants comes another form: the vitamin D₂. Avocado and sun-exposed mushrooms contain smaller amounts. Whether Vitamin D₂ and Vitamin D₃ exercise everywhere in the body same functions, is not yet finally clarified.

What is vitamin K and how can I take it to my body?

Vitamin K is another fat-soluble vitamin that was discovered in the mid-1930s. There are several forms: Vitamin K₁ and K₂. K₁ is found in green plants, i.e. lettuce, spinach, kale, and to a lesser extent in vegetable oils. K₂ is of bacterial origin, i.e. it occurs in fermented foods and in minute amounts in some animal foods. Nattō, a Japanese fermented soy product, is the only food source worth mentioning here. However, this product is hardly consumed by us. Vitamin K₂ is synthesized by our intestinal flora, but in the colon, a section of the intestine where the absorption of substances is no longer efficient. Vitamin K is responsible for a single biochemical reaction in the body, but it has many metabolic effects. The best known is the effect of vitamin K on blood clotting, especially through drugs such as Marcumar - a vitamin K antagonist (the substance prevents the effect of vitamin K). This inhibits blood clotting and helps many patients. However, there are side effects. There are changes in calcium and bone metabolism. Therefore, there are new preparations for "blood thinning" which do not have these effects. What is interesting is what vitamin K does in calcium and bone metabolism. There are two things: On the one hand it promotes the incorporation of calcium into the bones and on the other hand it prevents the deposition in the vascular walls and thus has an anti-arteriosclerotic effect. Vitamin D and vitamin K work best together in this way. Vitamin D ensures that the necessary calcium is absorbed by the body and prepares the bone cells for incorporation, while vitamin K guides the calcium in the right direction, i.e. directs calcium into the bones and prevents faulty deposition in blood vessels.

Who has an increased risk of vitamin D and K deficiency?

Basically the same people who are exposed to a vitamin D deficiency as described above. Risk groups are also older people, people with dark skin types, overweight people and people who are rarely exposed to direct sunlight. The same risk groups apply to vitamin K, which is a vitamin D-supporting vitamin. In addition, there are people who take blood thinners based on vitamin K antagonists. Other risk groups that are associated with certain diseases must be clarified with the treating physician, and the same applies to infants and children.

Our interview partner Prof. Dr. Tilman Grune

Prof. Dr. Grune studied medical biochemistry in Moscow. He then went to the Charité in Berlin, where he received his doctorate in 1992 and his habilitation in 1998. In the following years he first worked at the Charité in Berlin, then at the Institute for Environmental Medical Research at the University of Düsseldorf. In 2006, he received his first chair at the University of Hohenheim, Stuttgart, in the Department of Biofunctionality and Food Safety. Between 2011 and 2014, Prof. Dr. Grune was Director of the Institute of Nutritional Sciences at the University of Jena. Since 2014, he has been Scientific Director of the German Institute of Nutrition Research and Professor of Molecular Toxicology at the University of Potsdam. His focus is on vitamin metabolism, antioxidants and oxidative stress.