Learn about the role of vitamin K in cancer treatment and prevention. Explore the research, benefits, supplementation, and safety of vitamin K.
Table of Contents
- Vitamin K – What is it and where is it found?
- Anti-cancer properties of vitamin K: a review of studies
- Effect of vitamin K on cancer development and treatment
- Vitamin K in cancer prevention – can it prevent cancer?
- Symptoms of deficiency and recommended vitamin K supplementation
- Safety and side effects of vitamin K use
Vitamin K – What is it and where is it found?
Vitamin K is a group of fat-soluble chemical compounds that play an extremely important physiological role in the human body. The most significant representatives of this group are vitamin K1 (phylloquinone) and vitamin K2 (menaquinone), which differ in their chemical structure, origin, and range of action. Vitamin K1 is mainly found in green plants and is primarily responsible for maintaining proper blood clotting by activating proteins involved in this process. However, increasing research also indicates its impact on bone health and cellular processes. Vitamin K2, on the other hand, is produced by intestinal bacteria and found in fermented animal-based foods such as natto (a traditional Japanese dish made from fermented soybeans), blue cheeses, or certain types of meat. It is essential for the functioning of proteins regulating calcium metabolism, including osteocalcin and Gla-matrix protein, which help incorporate calcium into bone tissue and prevent its deposition in blood vessel walls, thereby reducing the risk of atherosclerosis and supporting cardiovascular health. Additionally, vitamin K supports metabolic functions, influences inflammatory processes, and—as suggested by recent studies—may play a role in inhibiting the formation and development of cancer cells, making it a particularly important dietary component in the context of cancer prevention.
When it comes to dietary sources, vitamin K1 is most abundant in leafy green vegetables such as spinach, kale, lettuce, broccoli, savoy cabbage, beet greens, and Brussels sprouts. Vitamin K2 is present in the previously mentioned fermented foods like natto, but its lower concentrations are also found in aged yellow cheeses (e.g., gouda, cheddar, emmental), meat, liver, eggs, and certain yogurts. Vitamin K deficiencies are relatively rare in healthy individuals with a properly functioning digestive system, as the body can partially synthesize vitamin K2 with the help of our natural gut microbiota. However, increasing data suggest that intake levels—particularly of vitamin K2—in Western diets are often insufficient. Adequate amounts of this vitamin protect not only against coagulation disorders (e.g., bleeding or bruising) but may also lower the risk of osteoporotic complications (bone fragility), heart disease, inflammation, and possibly the development of certain cancers such as lung cancer, prostate, lung, or stomach cancers. It is important to remember that the absorption of vitamin K is improved by the presence of fats in food, so the best strategy is to combine vitamin K-rich vegetables with vegetable oils, nuts, or avocado. Modern science is intensively researching both the functions and therapeutic potential of different forms of vitamin K, which has sparked justified interest in its role in the prevention and treatment of cancer and other chronic diseases.
Anti-cancer properties of vitamin K: a review of studies
A growing number of scientific studies point to a potentially significant role for vitamin K, both K1 and K2, in the prevention and treatment of cancer. Scholars are particularly interested in the mechanisms by which vitamin K may influence cellular processes related to tumorigenesis. In vitro studies have shown that vitamin K2 (menaquinone) can induce apoptosis—programmed cell death—in various types of cancer cells, including lung cancer, leukemia, and colorectal cancer. In laboratory studies, the use of vitamin K inhibited the proliferation of cancer cells by blocking the cell cycle, reducing telomerase activity, and regulating the expression of genes associated with cancer cell survival and growth. One of the principal mechanisms suspected for menaquinone is the generation of reactive oxygen species (ROS) within the cell, leading to mitochondrial damage and triggering a signaling cascade that results in apoptosis. Other reports indicate that vitamin K may inhibit angiogenesis—the formation of new blood vessels necessary for tumor growth—and limit the ability of cancer cells to migrate and metastasize. Notably, similar—albeit somewhat weaker—effects have also been observed for phylloquinone (K1), especially in cell models of colorectal and breast cancer.
Translating laboratory findings to clinical practice is the subject of increasing epidemiological and clinical research on humans. Population analyses suggest a relationship between higher vitamin K intake and a lower risk of certain cancers, especially liver, prostate, and breast cancer. One of the better-documented examples includes studies performed in Asian countries on groups of patients with hepatitis C, where vitamin K2 supplementation was associated with a reduced risk of progression to hepatocellular carcinoma and improved survival rates among those already affected by this disease. A Japanese study from 2004 showed that daily menaquinone supplementation in patients after tumor resection significantly reduced the risk of hepatocellular carcinoma recurrence. Similarly, in Europe, the EPIC (European Prospective Investigation into Cancer and Nutrition) cohort studies demonstrated that high vitamin K2 intake may relate to reduced risk of prostate cancer in men and some reduction in breast cancer risk. Nevertheless, this effect was not observed to the same extent for vitamin K1, suggesting significant differences in the metabolism and action of these vitamin forms. Although many results are promising, there is still a lack of large randomized clinical trials to clearly determine vitamin K’s effectiveness as supportive or preventive therapy in oncology. Limitations of existing studies include small sample sizes, variations in dosing and forms of vitamin K, and a lack of standardized supplementation protocols. Despite these reservations, researchers emphasize that due to its high safety profile and low risk of adverse effects, vitamin K could be a promising adjunct in cancer treatment strategies—especially in integrated approaches that combine diet, supplementation, and conventional oncology therapies.
Effect of vitamin K on cancer development and treatment
Scientific interest in the effects of vitamin K on cancer processes stems from increasing evidence indicating its active participation in the regulation of mechanisms responsible for both the formation and inhibition of cancer cell development. Vitamin K, encompassing both phylloquinone (K1) and menaquinones (K2), has shown in vitro the ability to interact with key signaling pathways in cancer cells. Above all, vitamin K2 is known to initiate apoptosis, which leads to the elimination of abnormally proliferating cells. This mechanism is crucial since apoptosis disruptions are a main component of tumorigenesis. Furthermore, vitamin K affects the generation of reactive oxygen species (ROS), which through cellular and DNA damage, can inhibit the proliferation of cancer cells and increase their sensitivity to the body’s repair mechanisms. Equally important is vitamin K’s role in modulating gene expression involved in cell division and differentiation. Studies have observed that K2 can influence signaling pathways such as p53 and Wnt/beta-catenin, which are critical in the development of various cancers, including the liver, colon, and prostate. Promising results also concern the impact of vitamin K on inhibiting angiogenesis—the process of creating blood vessels essential for tumor growth—and limiting cancer cell migration and invasion, which is significant for metastasis formation. Some experiments show that vitamin K can enhance the effectiveness of other treatments, such as chemotherapy or radiotherapy, by increasing cancer cell sensitivity to cytostatics while simultaneously protecting healthy tissues from oxidative stress.
Vitamin K in clinical studies and therapeutic perspective
Translating laboratory research to clinical reality is a considerable challenge, but an increasing number of epidemiological observations and clinical trials suggest that an optimal level of vitamin K in the diet and blood may be linked with a lower risk of cancer development and better outcomes in already diagnosed patients. Among the most remarkable scientific reports are those concerning liver cancer. In patients with hepatitis B and C—particularly exposed to liver cancers—vitamin K2 supplementation has demonstrated benefits such as delayed cancer progression, reduction of tumor size, and increased survival rates. Also, studies on prostate and breast cancer indicate potential benefits from a high intake of both K1 and K2—women with higher vitamin K intake are found to have a reduced risk of developing precancerous changes in breast tissue. Importantly, vitamin K seems to work synergistically with other components of an antioxidant-rich diet such as vitamin D or omega-3 fatty acids, which may further support cancer prevention strategies. Proposed therapeutic mechanisms also include vitamin K’s role in inhibiting chronic inflammation, a known factor predisposing to cancer development. Moreover, clinical studies confirm that vitamin K supplementation is generally well tolerated, rarely leading to adverse events—although caution is advised in those with coagulation disorders or on anticoagulant drugs. As existing data is largely based on observations and small trials involving cancer patients, scientists emphasize the need for further large-scale, randomized studies encompassing different cancer types, populations, and supplemental doses and forms of vitamin K. Nevertheless, current findings indicate that optimizing vitamin K intake—through diet and, if needed, supplementation—may be a valuable support in prevention and possibly as adjunct cancer therapy, particularly in at-risk groups and patients with increased requirements for this nutrient.
Vitamin K in cancer prevention – can it prevent cancer?
In recent years, vitamin K has gained recognition not only as an essential factor in coagulation and bone metabolism but also as a potential agent in cancer prevention. An increasing number of epidemiological and experimental studies suggest that both phylloquinone (K1) and menaquinones (K2) may play a significant role in cancer prevention by influencing key cellular processes that determine tumor initiation and progression. One primary mechanism attributed to vitamin K’s preventive abilities is its capacity to regulate the cell cycle and promote apoptosis—the body’s natural means for eliminating damaged or potentially mutated cells. This hampers the accumulation of abnormal cells which could later form cancerous lesions. Additionally, vitamin K reduces oxidative stress and the production of free radicals, protecting cells from DNA mutations that often represent the first step of cancer transformation. Scientific research has also demonstrated that especially vitamin K2 can modulate the Wnt/beta-catenin signaling pathway, which is aberrantly activated in many cancers and leads to uncontrolled cell growth and division. These mechanisms make vitamin K an interesting candidate for preventive use in high-risk groups, such as those with a family history of cancer, chronic inflammation, or metabolic disorders.
Analysis of cohort population studies conducted across Europe and Asia reveals a connection between high vitamin K intake—especially K2—and lower risks for certain cancers, such as colorectal cancer. For example, renowned Japanese studies involving postmenopausal women found that those with the highest K2 intake had significantly lower risks of developing liver and breast cancers compared to those with the lowest intake. Similarly, the German EPIC-Heidelberg study confirmed that higher K2 consumption correlated with reduced incidence of prostate cancer. While vitamin K1 also offers benefits, its effect on cancer prevention is less pronounced, likely due to weaker tissue penetration outside the liver and different bioavailability. The presence of vitamin K in daily diets—especially those rich in fermented products, cheese, leafy greens, and some animal products—may thus be an element of integrated cancer prevention. However, the mechanisms involved and optimal vitamin K dosages for cancer prevention remain the subject of intensive research. There are currently no definitive supplementation guidelines for the entire population, but supplementation may be especially valuable in individuals with limited absorption, intestinal issues, or long-term antibiotic use. Importantly, available clinical data confirm the safety of both K1 and K2, even in higher doses, provided regular monitoring—especially for patients on anticoagulants. Based on current research, maintaining high vitamin K levels through natural diet or targeted supplementation can support cancer prevention strategies, particularly in combination with other healthy habits such as regular physical activity and avoiding harmful substances.
Symptoms of deficiency and recommended vitamin K supplementation
Vitamin K deficiency in adults is not common, but its occurrence can have serious health consequences, especially in the context of blood clotting mechanisms and cellular repair processes. The most characteristic symptom of vitamin K deficiency is coagulation disorders, manifested by prolonged bleeding, frequent bruising, bleeding gums and nose, and—in severe cases—internal hemorrhages. Children and newborns, who are particularly vulnerable due to an immature enzymatic system and low vitamin K content in breast milk, may exhibit symptoms of hemorrhagic disease, including gastrointestinal bleeding, cerebral hemorrhage, or hematuria. In adults, aside from clotting issues, long-term deficiency can lead to decreased bone mineral density and an increased fracture risk since vitamin K is involved in activating osteocalcin and other proteins responsible for incorporating calcium into bone structure. Recent reports also indicate that a chronic K2 deficiency may intensify inflammatory processes and negatively impact the prevention of chronic diseases, including cancer. At-risk groups for vitamin K deficiency include individuals with fat malabsorption (celiac disease, cystic fibrosis, chronic liver and biliary tract diseases), patients following bariatric surgery, those on very low-fat diets, people on long-term antibiotics (which destroy gut flora producing K2), and the elderly, in whom nutrient absorption tends to be reduced.
If a vitamin K deficiency is diagnosed or suspected, supplementation may be necessary, but it should be agreed on with a doctor—especially for patients on anticoagulants (vitamin K antagonists like warfarin), as interactions can disrupt anticoagulant therapy. For healthy adults, the recommended daily intake is approximately 75–120 µg (values may vary by country and authority), with slightly higher needs during pregnancy and lactation. Vitamin K1, found mainly in leafy green vegetables, is well-absorbed, especially when eaten with plant oils; K2, present in fermented foods and some animal products, accumulates better in tissues and remains in the blood longer, making its supplementation often suggested in targeted osteoporosis, cardiovascular disease, or as an element supporting cancer prevention. Dietary supplements with vitamin K2 are commonly available as menaquinone-7 (MK-7), which provides high bioavailability and efficacy. Noteworthy dietary sources include natto, hard cheese, pickles, egg yolks, and liver—valuable especially for those limiting green vegetable intake. Supplementing vitamin K is generally well tolerated, and excess intake is not toxic due to the body’s ability to excrete it. An exception is the synthetic form menadione (K3), which is toxic and should not be used as a human supplement. Monitoring vitamin K intake and blood levels is especially important in chronically ill individuals, those with digestive disorders, the elderly, and pregnant women. According to the Polish Neonatal Society’s guidelines, newborns receive prophylactic doses of vitamin K to prevent rare but life-threatening hemorrhages. Optimizing the diet for vitamin K presence—and supplementation if necessary—are key elements in preventing deficiencies, which can have both short- and long-term health consequences, particularly related to severe bleeding complications, bone weakness, inflammation, and potential cancer risk.
Safety and side effects of vitamin K use
Vitamin K, especially in its natural K1 (phylloquinone) and K2 (menaquinone) forms, is considered one of the safest micronutrients. Its toxicity is exceptionally low, and side effects at recommended dosages are very rare. For adults obtaining vitamin K through diet or recommended supplemental doses, overdoses are virtually nonexistent. Studies show that the body has effective mechanisms to prevent accumulation even at comparatively high intakes, distinguishing it from other fat-soluble vitamins. A crucial issue is the difference between forms: K1 and K2 widely used in foods and supplements, and the synthetic K3 (menadione), which is not recommended for human supplementation due to its much higher risk of adverse effects. Large population studies show that even prolonged K1 or K2 supplementation does not lead to serious side effects, and rare reactions like allergies, nausea, or mild skin symptoms after high doses are usually temporary and mild. Importantly, vitamin K does not cause typical overdose symptoms such as hypercalcemia seen with excess D3 or A vitamins. For this reason, there is no established upper limit (UL) for healthy adults. Children, pregnant women, and older people can also safely benefit from vitamin K supplementation for both cancer prevention and hematological support—provided they follow recommended doses.
The most significant safety concern with vitamin K is among users of anticoagulant drugs, particularly vitamin K antagonists (e.g., warfarin, acenocoumarol). Uncontrolled high-dose supplementation may significantly decrease the effectiveness of anticoagulants, posing a serious health threat. Accordingly, vitamin K supplementation in those with chronic cardiovascular disease, especially on anticoagulants, should always be closely supervised by a physician with individual recommendation and regular blood clotting monitoring (INR). Even small changes in vitamin K intake in these patients may require adjustment of drug dosing. Other potential adverse effects, when they occur, are rare and mostly limited to gastrointestinal symptoms (such as abdominal discomfort or diarrhea after high supplement doses), allergic reactions (rashes, itching, edema), or temporary changes in blood morphology. For newborns, who routinely receive prophylactic doses, safety is well established by years of practice and numerous studies, with adverse effects being exceptionally rare (e.g., local swelling after intramuscular injection). In healthy adults, prolonged supplementation, especially at or moderately above daily requirements, does not lead to accumulation or organ dysfunction. The main exception is the synthetic form menadione (K3), which is toxic in humans and laboratory animals—associated with risks of liver damage, jaundice, hemolytic anemia, and allergic responses. Its use is therefore virtually banned in food supplements and medicines for humans. For healthy individuals obtaining vitamin K from food (green leafy vegetables, fermented dairy, pickles, egg yolks), the risk of adverse effects is negligible. Supplementation with vitamin K2 (MK-7, MK-4) is highly safe and not associated with specific health issues, even with use over many months. In summary, both natural K1 and K2 can be safely taken by most people—provided dosage sensibility and particular care in those on anticoagulation therapy or with serious chronic diseases.
Summary
Vitamin K plays a crucial role in the body, and its anti-cancer properties are confirmed by numerous scientific studies. It may slow the progression of certain cancers and support the effectiveness of oncological treatment. Regular vitamin K intake is vital for both cancer prevention and general health. Deficiency of this vitamin can increase disease risk, so ensuring adequate levels through diet or supplementation is important. However, always consult your doctor before starting supplementation to avoid possible side effects.
