The link between the blood thinner warfarin and soyfood consumption is not immediately apparent. However, issues regarding this association do occur from time to time, as when a vegan recently voiced concern about ingesting soyfoods due to his warfarin treatment. This concern is, for the most part, unfounded. The vitamin K level of soy is a big factor in this association, but it’s not the only one. Let’s take a look at the numbers, starting with some background information on warfarin and vitamin K.
Warfarin has been used as an anticoagulant for approximately 70 years.
Thromboembolism (obstruction of a blood vessel by a blood clot that has gotten dislodged from another place in the circulation) and different cardiovascular disorders such as atrial fibrillation are among the indications for its use (irregular heartbeat that can lead to blood clots, stroke, heart failure). Warfarin works by blocking the vitamin K epoxide reductase complex 1, an enzyme that is required for vitamin K activation in the body.
Vitamin K is a fat-soluble vitamin that serves as a coenzyme in the creation of the biologically active version of several proteins involved in blood coagulation and bone metabolism.
2 Vitamin K has been studied in the fields of osteoarthritis, diabetes, vascular disease, cognitive function, and fractures, among other things. 7 Vitamin K comes in two forms: phylloquinone (vitamin K1) and a group of menaquinones (vitamin K2). The former is found primarily in plants, particularly green leafy vegetables; the latter is primarily bacterial in origin and can be found in small levels in a variety of animal-based and fermented meals.
Because warfarin works by suppressing vitamin K action, individuals who take it must be careful about how much vitamin K they ingest. Too much of a good thing can reduce the drug’s effectiveness, increasing the danger of blood clots. Excessive bleeding could occur if you don’t get enough vitamin K. The idea is to maintain a constant vitamin K intake so that blood levels can be titrated appropriately. Men and women over the age of 20 in the United States eat on average 118 and 123.5 ug/d of vitamin K, respectively,8 which just about meets the necessary intake for men and surpasses it by almost one-third for women (table 1). So, given that context, how does soy fit into the picture?
The report that sparked the most worry about soy eating by warfarin patients came out in 2002. It depicts a 70-year-old Caucasian man on warfarin who got subtherapeutic international normalized ratio (INR) readings as a result of soymilk drinking, according to the report. 9 A subtherapeutic INR shows that the blood thinner warfarin was not working properly. “Healthcare providers should be aware to the potential ramifications of this food/drug combination,” the report’s author stated. However, this was not the first time that a soy-warfarin interaction had been reported in the literature.
The earliest mention of this interaction may have been in 1978, when it was hypothesized that the fermented soybean product natto could counteract warfarin’s effects.
10 It’s hardly surprising that this piece received little attention because it was written in Japanese and covered a delicacy that is rarely eaten outside of Japan. Kudo11’s investigation a decade later corroborated the original report. So, what’s the deal with this interaction? Vitamin K is the answer.
Natto has an extraordinarily high vitamin K content, as indicated in table 2, with one serving providing many times the daily amount. In addition, the majority of vitamin K in natto comes in the form of MK-7. MK-4 through MK-13 are the names given to menaquinones based on the length of their side chains. The most well-studied menaquinones are MK-4, MK-7, and MK-9. Although there is little information on the relative bioavailability of different types of vitamin K supplements, Schurgerset al.12 discovered that MK-7 is well absorbed and has a long half-life, resulting in stable and high serum levels. Hematologists should be aware that preparations containing 50 ug/d or more of MK-7 may interfere with oral anticoagulant medication in a clinically meaningful way, according to these authors.
The fermentation of Bacillus subtillis, which produces vitamin K, results in a high concentration of vitamin K in natto. In fact, after eating natto, this bacterium continues to manufacture vitamin K in the colon for several days. 14 Natto’s high vitamin K content could explain why this cuisine has lately been linked to a lower risk of osteoporotic fractures in Japanese women. 15 Vitamin K is involved in the gamma-carboxylation of osteocalcin, a bone mineralization protein. 16 However, because of the high vitamin K concentration of natto, it is suggested that warfarin users avoid it. 17 But what about soyfoods that aren’t soy?
Table 2 shows that two forms of tofu give roughly 12 ug/100 g, despite the fact that another variety had significantly greater values, but nothing like natto or broccoli, cabbage, and spinach. And, while there is a variation, most soymilks contain less than 10 ug/cup. 18 A cup of boiling soybeans has 33 ug of potassium, but it also has more than 30 grams of protein. 18 Although soybean oil is substantially higher in vitamin K than other oils, a tablespoon only offers around 21% and 28% of the recommended daily consumption for adult men and women, respectively. 18 As a result, most soyfoods have no need to be avoided because of their vitamin K concentration.
Finally, what may have caused the previously reported interaction between soymilk and warfarin, given that the patient’s soymilk contained less than 1 ug vitamin K? The author of this case report believed that the isoflavones in soy may have influenced warfarin absorption and metabolism, but the answer remains unknown. However, the soymilk ingested likely provided no more than 25 mg of isoflavones, which is a modest quantity when compared to the usual intake of 25 to 50 mg per day among older Japanese males. 19 If isoflavones do alter the efficacy of warfarin, one could fairly wonder why more examples of soy interacting with it have not been documented.
In conclusion, there appears to be no evidence that warfarin patients should avoid soyfoods, with the exception of natto.
Table 3: Vitamin K Content of Selected Oils per Tablespoon (14 g) based on USDA National Nutrient Database Standard Reference Release 2818.
- JE Ansell, JE Ansell, JE Ansell, JE Ansell, JE Ansell, JE Ansell, JE Ansell, JE Ansell, JE Ansell, JE Ansell, JE Ansell, JE Ansell, JE Ansell, JE Ansell
- The Institute of Medicine is a non-profit organization dedicated to the advancement The Food and Nutrition Board is a non-profit organization that promotes healthy eating Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc Dietary Reference Intakes National Academy Press, Washington, DC, 2001.
- A review of current information on the association between vitamin K and osteoarthritis, Chin KY. 2020;12;12;12;12;12;12;12;12;12;12;12 (5).
- Effect of soy milk on warfarin effectiveness, Cambria-Kiely JA. 2002;36(12):1893-6. Ann Pharmacother. 2002;36(12):1893-6.
- Warfarin antagonism of natto and natto consumption enhance serum vitamin K. Kudo T. 17189-201. Artery. 1990;17189-201.
- Rasouli-Ghahroudi AA, Akbari S. A overview of the most recent findings from preclinical investigations on vitamin K and bone metabolism. 2018;20184629383. BioMed research worldwide.
- M. Messina, C. Nagata, and A. H. Wu. Adult Asian soy protein and isoflavone intake estimates. 2006;55(1):1-12 in Nutr Cancer.
Is K2 present in soy sauce?
One of the most important advantages of fermented soya is that it is the best food source of vitamin K2, which is necessary for avoiding osteoporosis, cardiovascular disease, brain diseases like dementia, and even cancer.
Is it OK to eat soy when on Coumadin?
Warfarin (Coumadin) is a blood thinning medication. Warfarin’s effectiveness has been reported to be impaired by soy (Coumadin). Warfarin (Coumadin) efficacy being reduced may raise the risk of clotting. The reason for this interaction is unknown.
Is vitamin K present in soybean oil?
This oil, like canola, is high in phylloquinone, the most common type of vitamin K. A tablespoon of soybean oil contains around 25 micrograms of vitamin K, while a tablespoon of canola oil contains approximately 10 micrograms.
Is soy milk a good source of vitamin K?
Soybeans contain a lot of vitamin K, according to your website.
Does this mean that a Coumadin patient cannot drink soymilk? What would you propose, given that dairy products don’t agree with me?
Dr. Gourmet Says…
Soy milk contains only a small quantity of Vitamin K. Vitamin K is found in roughly 7 micrograms (mcg) per cup. This is a modest dose of Vitamin K, thus it should be safe for persons on Coumadin (warfarin).
Is it safe to use soy sauce?
Soy sauce is usually used in tiny amounts. As a result, there aren’t likely to be significant health benefits. Soy contains isoflavones, which are substances that have been linked to a variety of health advantages, including easing menopause symptoms and lowering cholesterol. Tofu or other soy products, such as soy milk, may be a better alternative if you want to reap the benefits of soy in your diet.
Antioxidants. Dark soy sauce may be high in antioxidants, according to a study. Free radical damage to cells can be delayed or prevented by antioxidants. However, because the evidence is limited, further research is needed to be certain.
Sodium content is high. One tablespoon of soy sauce has about 40% of the daily salt allowance of 2,300 milligrams. Salt is a nutrient that our bodies require to function properly. Too much of it, on the other hand, can raise blood pressure and cause heart disease and stroke. On a daily basis, the average American consumes more than 3,400 mg of sodium.
Allergens. Allergies to soy are frequent, especially among children. Soy sauce also includes wheat, which may cause allergic reactions in certain people. Others may suffer from celiac disease, an autoimmune illness brought on by gluten consumption.
Although most soy sauces contain wheat, several manufacturers offer gluten-free options. If you have any allergies, check the label for ingredients. Tamari is a type of soy sauce that can be prepared with less or no wheat.
Is vitamin K2 present in tofu?
Unfortunately, vitamin K2 is not vegan. Vitamin K2 is mostly prevalent in animal tissues and organs, particularly in grass-fed animals. Dairy products, organ meats, and normal beef, pig, eggs, poultry, and fish are the most major sources.
Vitamin K1 is more vegan-friendly, and fruits and vegetables provide half of your vitamin K.
When opposed to vitamin K2, you can receive vitamin K1 from a lot more foods.
In a typical diet, you’d obtain ten times the quantity of vitamin K2 you’d get from vitamin K2.
Vitamin K1 deficiency is unlikely because a Western diet will quickly help you meet the necessary intakes.
On the other hand, vitamin K2 contributes for just around 25% of total vitamin K intake from diet. As a result, you’re taking a supplement, which is a good thing to think about!
The good news is that your body can convert some vitamin K1 to K2 (but not enough). The MK-4 side chain is produced in your body by microorganisms.
Is vitamin K2 present in miso?
What distinguishes natto from other fermented soy products such as miso and tempeh, and why is it more beneficial? Here are three probable causes; there are many more that are feasible and even likely:
Natto fermentation produces a large amount of Vitamin K2 (MK-7), but miso and tempeh fermentation do not. Vitamin K2 can only be made by a few types of bacteria, the most common of which is the natto-fermenting Bacillus subtilis. Fermentation of miso and tempeh is mediated by fungus (Aspergillus and Rhizopus genuses, respectively) that do not produce Vitamin K2.
Natto contains nattokinase, a naturally occurring blood thinner (named after the food it comes from). This enzyme, which is more usually seen in the West as an isolated supplement, has been demonstrated in vitro and in vivo to prevent and dissolve blood clots. Oral nattokinase has also been shown in clinical research to reduce blood pressure and the risk of stroke.
Bacillus subtilis is a probiotic bacteria that is a well-known member of the human gut microbiome. It has been shown to have good effects on inflammation and immunology in human health, which are factors that could affect cardiovascular health. On the other hand, there is currently minimal evidence that the fungi that dominate miso and tempeh fermentations operate as probiotics.
In the United States, cardiovascular disease is the leading cause of death. Eating a heart-healthy diet is an important element of everyday preventative care, and evidence suggests that eating fresh fermented natto is one of the best options.
Does soy sauce have an impact on INR?
Soybeans are produced by the soy plant, which is a leafy green plant. Nowadays, soy is used in a variety of goods. The vitamin K contained in the soy bean influences soy bean formulations, especially soy milk.
The fact that soybean products lower a patient’s international normalized ratio (INR) value over time has been cited by several publications; however, the amount of soy consumed has not been determined.
Patients on warfarin should maintain a steady soy intake. Patients who are thinking about adding or eliminating soy from their diet should talk to their anticoagulation practitioner first because their warfarin dose may need to be modified. Patients who consume soy products may generally require somewhat greater warfarin doses. Although soy is not contraindicated for warfarin users, thorough communication regarding all dietary changes is required to keep the INR stable. Interactions between soy proteins and warfarin may be more widespread than the literature shows, and further research is needed to pinpoint the specific mechanism. The potential consequences of this food-drug combination should be made known to health care practitioners.