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Inhaltsstoff-Glossar
Vitamin K
What Is Vitamin K?
Vitamin K (quinone) is an essential nutrient and, together with vitamins A, D, and E, belongs to the four fat-soluble vitamins. In the 1920s, unexplained bleeding in cattle and chickens puzzled veterinarians until scientists discovered the role of vitamin K in blood clotting (coagulation). The vitamin was simply named "K" after coagulation. Vitamin K plays an important role in the body as a cofactor for numerous enzymes involved in calcium metabolism. It is commonly supplemented to support cardiovascular health and is often taken together with vitamin D.
Where Does Vitamin K Naturally Occur?
There are two natural sources of vitamin K: green plants provide vitamin K1, while bacteria produce vitamin K2. Humans obtain vitamin K through their diet, but vitamin K produced by bacteria in the intestinal microbiota is also believed to contribute to the body's supply.
Vitamin K1 (phylloquinone) is particularly abundant in photosynthetically active plant tissues such as spinach leaves, lettuce, and parsley. This form accounts for the majority of dietary vitamin K intake but has relatively lower bioavailability.
Animal-derived and fermented foods such as liver, muscle meat, cottage cheese, cheese, and eggs contain high concentrations of vitamin K2 (menaquinone). Microorganisms in fermented foods—including the traditional Japanese dish natto as well as cottage cheese and cheese—produce this vitamin themselves. Animal products contain vitamin K2 because animals convert vitamin K1 from plant-based feed into vitamin K2.
Vitamin K2 comprises a group of menaquinones with side chains of varying lengths, designated as "MK-n." The most common forms are vitamin K2 MK-7 (with seven isoprene units in its side chain), which is synthesized by bacteria, and MK-4 (with four isoprene units), which is produced in animals through the conversion of plant-derived vitamin K1. Vitamin K2 MK-7 is regarded as the form with the highest bioavailability. There is also the synthetic form, vitamin K3, which is biologically active as well. However, only vitamin K1 and vitamin K2 are approved for use as food additives.
Vitamin K is heat-stable, and its absorption can be enhanced when consumed together with dietary fats and oils. Within the body, vitamin K is stored primarily in the liver. Total body stores are relatively small, amounting to approximately 70–100 micrograms. According to the German Nutrition Society (DGE), the recommended daily intake is 70–80 micrograms for men and 60–65 micrograms for women. From the age of 50 onward, the higher intake recommendation applies.
Vitamin K1 (phylloquinone) is particularly abundant in photosynthetically active plant tissues such as spinach leaves, lettuce, and parsley. This form accounts for the majority of dietary vitamin K intake but has relatively lower bioavailability.
Animal-derived and fermented foods such as liver, muscle meat, cottage cheese, cheese, and eggs contain high concentrations of vitamin K2 (menaquinone). Microorganisms in fermented foods—including the traditional Japanese dish natto as well as cottage cheese and cheese—produce this vitamin themselves. Animal products contain vitamin K2 because animals convert vitamin K1 from plant-based feed into vitamin K2.
Vitamin K2 comprises a group of menaquinones with side chains of varying lengths, designated as "MK-n." The most common forms are vitamin K2 MK-7 (with seven isoprene units in its side chain), which is synthesized by bacteria, and MK-4 (with four isoprene units), which is produced in animals through the conversion of plant-derived vitamin K1. Vitamin K2 MK-7 is regarded as the form with the highest bioavailability. There is also the synthetic form, vitamin K3, which is biologically active as well. However, only vitamin K1 and vitamin K2 are approved for use as food additives.
Vitamin K is heat-stable, and its absorption can be enhanced when consumed together with dietary fats and oils. Within the body, vitamin K is stored primarily in the liver. Total body stores are relatively small, amounting to approximately 70–100 micrograms. According to the German Nutrition Society (DGE), the recommended daily intake is 70–80 micrograms for men and 60–65 micrograms for women. From the age of 50 onward, the higher intake recommendation applies.
What Is the Primary Function of Vitamin K in the Body?
According to the European Food Safety Authority (EFSA), vitamin K has been scientifically proven to contribute to normal blood clotting and the maintenance of normal bones. Vitamin K fulfills these functions as a cofactor in the synthesis of proteins involved in blood coagulation and bone formation. These proteins include clotting factors, plasma proteins, and the Gla proteins found in bone-forming osteoblasts, all of which require vitamin K for their production.
These observations have led to the hypothesis that vitamin K status may be associated with the risk of arterial calcification and bone loss. In arterial calcification, medically referred to as atherosclerosis, calcium, blood lipids, and other substances form plaques that reduce blood flow, increase blood pressure, and damage blood vessel walls. In osteoporosis, bone minerals such as calcium are progressively lost, resulting in fragile bones and an increased risk of spontaneous fractures.
It is therefore well established that adequate vitamin K levels are necessary for the normal function of these physiological processes. Whether specific doses of vitamin K can help prevent the development of atherosclerosis, osteoporosis, or other diseases remains an important area of ongoing scientific research and has not yet been conclusively established.
These observations have led to the hypothesis that vitamin K status may be associated with the risk of arterial calcification and bone loss. In arterial calcification, medically referred to as atherosclerosis, calcium, blood lipids, and other substances form plaques that reduce blood flow, increase blood pressure, and damage blood vessel walls. In osteoporosis, bone minerals such as calcium are progressively lost, resulting in fragile bones and an increased risk of spontaneous fractures.
It is therefore well established that adequate vitamin K levels are necessary for the normal function of these physiological processes. Whether specific doses of vitamin K can help prevent the development of atherosclerosis, osteoporosis, or other diseases remains an important area of ongoing scientific research and has not yet been conclusively established.
What Are the Benefits of Vitamin K Supplementation?
Several cross-sectional studies and randomized controlled trials (RCTs) have shown that vitamin K status or supplementation can improve certain markers of bone health. In particular, low vitamin K intake appeared to be associated with bone loss in female participants. Overall, however, the available evidence is inconsistent, and the level of scientific evidence remains limited.
In a meta-analysis of nine randomized controlled trials conducted by a Canadian research group investigating the effects of vitamin K supplementation on arterial calcification and vascular damage, vitamin K increased the activity of an enzyme that helps prevent calcium deposition within blood vessels. However, the authors found no strong evidence that vitamin K supplementation effectively prevents or treats atherosclerosis. Further research is needed to determine whether vitamin K can prevent vascular calcification or improve existing atherosclerotic disease.
Like vitamin K, vitamin D is an essential nutrient for bone health. Studies have demonstrated that combining both vitamins in a single supplement enhances their beneficial effects on bone mineral density. Particularly in individuals with a high calcium intake—as is common in Western societies—the combination may help protect against calcium deposits that could develop as a result of excessive vitamin D intake.
Because there is currently no reliable biomarker for assessing the body's vitamin K status, nor sufficiently reliable data on the vitamin K content of foods, the German Federal Institute for Risk Assessment (BfR) classifies vitamin K as a Category 2 nutrient. According to the BfR, there is a certain degree of uncertainty regarding vitamin K supply and the potential development of deficiency.
If dietary intake is insufficient to meet vitamin K requirements, pharmacy-grade oral supplements providing 50–150 micrograms per day are available. In cases of life-threatening bleeding, up to 10 mg of vitamin K may be administered intravenously. Risk groups for vitamin K deficiency include individuals with eating disorders, inflammatory bowel diseases such as Crohn's disease, patients taking medications that interfere with the vitamin K cycle (including coumarin derivatives and certain antibiotics), as well as newborns and infants.
The BfR considers the risk of vitamin K overdose to be moderate and the risk of adverse effects to be low. Toxic reactions such as allergic responses or cardiac arrhythmias have been observed only rarely and primarily after intravenous administration of large doses. For individuals taking anticoagulant medications, the BfR considers a daily vitamin K intake of up to 100 micrograms to be safe. Higher intakes may result in life-threatening complications and should only be taken under medical supervision.
References
Further information and scientific studies on the active ingredient vitamin K can be found here.
Vitamin K and Osteoporosis: Myth or Reality?
pubmed.ncbi.nlm.nih.gov/28403946