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Bone Health



Nattokinase is an enzyme that has been present in the Japanese food natto for thousands of years, and recent studies have shown it to have anticoagulant properties. But we can’t really talk about nattokinase without talking about how fortunate you are to not have to eat natto anymore to reap the benefits. To the uninitiated, natto is scary. It’s a traditional Japanese dish of fermented soybeans that has been a staple in the Japanese diet for thousands of years.

Exactly how many thousands of years cannot be determined, but the things needed to make natto—beans, straw, water, and time—have been available in Japan for centuries. Natto is made by soaking soybeans in water for up to a day, then steaming the beans for several hours and finally mixing the beans with a sauce and rice straw and allowing it to ferment for twenty-four hours.

The magic of natto takes place when the bacterium Bacillus natto, present on the rice straw, is combined with the soybeans. This is how nattokinase is born. Without the bacterium, natto would be just another bowl of stinky beans.

An important development in the history of natto occurred in the early twentieth century when researchers discovered a way to introduce Bacillus natto into the soybean mix without using straw, therefore simplifying the process of making natto and producing more consistent results.

Natto’s sticky appearance and strong odor—if you like blue cheese you’ll love natto!—are an acquired taste, and even in Japan natto is mostly eaten in the eastern region of Kanto.

Nutritional information from the United States Department of Agriculture states that natto is “very low in cholesterol and sodium. It is also a good source of protein, Vitamin K, magnesium and copper, and a very good source of iron and manganese.”

As a good source of vitamin K, natto contributes to the formation of calcium-binding groups in proteins, assisting the formation of bone and preventing osteoporosis. Vitamin K1 is found naturally in seaweed, liver, and some vegetables, while vitamin K2 is found in fermented foods like cheese and miso. Natto has very high quantities of vitamin K2.

Japanese pets have also enjoyed natto as an ingredient in their food, and it has allegedly improved their health. The animals also don’t seem to mind natto’s smell and sliminess.

In spite of its smell and appearance, natto has a surprisingly mild taste and has been used in Japan for years as a folk remedy to treat heart and vascular diseases as well as fatigue and beriberi.


The scope and degree of the benefits of nattokinase were not documented until fairly recently. Its potent thrombolytic (clot-busting) activity is what’s currently gaining nattokinase attention and credibility.

Japanese researcher Dr. Hiroyuki Sumi studied thrombolytic enzymes while at the University of Chicago Medical School majoring in physiological chemistry. He wanted to find a natural enzyme that would help dissolve blood clots associated with heart attacks and strokes.

In 1980, Dr. Sumi tested over 173 natural foods as part of his research. You can imagine his joy when he dropped natto in a petri dish containing fibrin (a protein that forms in the blood to stop excess blood loss after trauma or injury and is chemically similar to thrombus) and within eighteen hours the natto had completely dissolved the fibrin.

Heart disease and stroke are the first and third most common causes of death in the United States. They account for more deaths than all cancers and injuries combined. To have discovered a supplement that originates from a natural source, has already been in use for thousands of years, and has a number of additional benefits—including lowering blood pressure—is a great leap forward in the quest to prevent cardiovascular disease.


Fibrin is a natural protein in our blood. When strands of fibrin accumulate in our blood vessels, blood clots form. Individual strands of fibrin are always present, but they undergo a chemical change and will stick together to form a blood clot as the body’s natural response to injury or trauma. This clotting process is a vital function, but problems occur when the body is unable to completely break down the clots once they have served their purpose.

The body produces more than twenty enzymes to produce blood clots, but only one to eliminate them. Plasmin is the body’s natural enzyme for breaking down blood clots. If too little plasmin is produced, then blood clots are not completely dissolved and the fragments will flow through the bloodstream, damaging blood vessel linings and sometimes blocking blood vessels completely.

A blood clot can block the flow of blood to muscle tissue. Blood carries oxygen, and if that oxygen supply is cut off, the tissue will eventually die. In the heart, a blood clot can result in angina and heart attacks. A blood clot in the chambers of the heart can move to the brain and cause a stroke.

Aging patients are the most likely to benefit from the blood-thinning effects of nattokinase. As the body ages, plasmin production decreases, which makes the blood more likely to coagulate, thus leading to a possible heart attack or stroke. Nattokinase’s ability to improve circulatory health will be most beneficial to those who suffer from conditions involving clogged arteries, such as patients with senile dementia caused by blocked cerebral arteries.

Nattokinase is a natural enzyme that complements the body’s natural production of plasmin. It is capable of potently dissolving fibrin as well as activating the prourokinase pathways to stimulate the body to produce its own plasmin. This complementary ability works in contrast to current pharmaceutical drugs, which can interfere with the normal clotting process. Most drugs are formulated to inhibit platelet aggregation, or the blood’s ability to clot. Nattokinase, on the other hand, seems to clean up old blood clots that would otherwise circulate through the bloodstream and cause damage to blood vessels.

“In all my years of research as a professor of cardiovascular and pulmonary medicine, natto and nattokinase represent the most exciting new development in the prevention and treatment of cardiovascular-related diseases,” said Dr. Martin Milner of the Center for Natural Medicine in Portland. Dr. Milner and Dr. Kouhei Makise of Kyoto, Japan, collaborated on a research project on nattokinase and wrote an extensive paper on their findings.

“We have finally found a potent natural agent that can thin and dissolve clots effectively, and with relative safety and without side effects,” said Dr. Milner.


Risk factors are traits that are used to measure a person’s likelihood to develop a disease. The more risk factors you have, the greater your risk. While many factors are hereditary, you do have control over many factors on the list.

• High cholesterol

• Family history

• High blood pressure

• Overweight

• Smoking

• Physical inactivity


• Stop smoking!

• Exercise

• Eat a diet rich in whole-grain foods and fiber

• Drink eight to ten glasses of water per day

• Engage in regular muscle strength training

• Practice a stress-reduction technique

A study conducted in 2002 noted that a mouthwash containing a unique cranberry compound was able to break up the dental plaque formed by a number of oral bacteria and decrease the salivary level of the Streptococcus mutans bacteria that causes tooth decay.


To date, seventeen studies have been devoted to natto and nattokinase, including two human trials. In 1990, Dr. Sumi and his research team published a series of reports on their findings on the clot-dissolving properties of nattokinase.

In the latest human study, researchers from JCR Pharmaceuticals, Oklahoma State University, and Miyazaki Medical College tested nattokinase on twelve healthy Japanese volunteers—six women and six men between the ages of twenty-one and fifty-five. The volunteers were given 7 ounces of natto before breakfast, and researchers then tracked fibrinolytic activity (or breakdown of fibrin) through a series of blood tests.

In one test, a blood sample was taken and a clot was artificially induced. The amount of time needed to dissolve the clot was cut in half within two hours of treatment, compared to the control group. The volunteers also retained the ability to dissolve blood clots for up to eight hours.

On average, the volunteers’ ELT (a measure of how long it takes to dissolve a blood clot) dropped by 48 percent within two hours of treatment.

The control group in the study ate only boiled soybeans, and their blood tests showed no significant fibrinolytic activity.

Dr. Sumi’s team conducted a test on two groups of dogs in which one group received nattokinase tablets and the other group received a placebo. The team then created a clot in a major leg vein in each dog that completely blocked the vein. Within five hours, the nattokinase-fed dogs had a complete restoration of circulation in their leg veins, while the dogs fed the placebo still had a complete vein blockage eighteen hours later.

Researchers from Biotechnology Research Laboratories and JCR Pharmaceuticals Company of Kobe, Japan, tested nattokinase’s ability to dissolve a blood clot in the carotid arteries of rats. Animals treated with nattokinase regained 62 percent of blood flow compared with those treated with plasmin that only regained 15.8 percent of blood flow.

And finally, in another laboratory study, endothelial (the inner lining of blood vessels) damage was induced in the femoral arteries of rats that had been given nattokinase. In normal circumstances, a thickening of arterial walls and blood clotting would occur, but they were both suppressed because of nattokinase’s fibrinolytic activity.


Although used as a traditional folk medicine in Japan to treat high blood pressure, recent studies confirm this benefit of nattokinase. In 1995, the effects of nattokinase on high blood pressure was studied in both animals and humans at Japan’s Miyazaki Medical College and Kurashiki University of Science and Arts.


Volunteers with high blood pressure were given 30 grams of natto extract (equivalent to 7 ounces of natto food), for four days. In four out of five volunteers, their systolic blood pressure dropped about 10.9 percent on average, and their diastolic blood pressure dropped about 9.7 percent on average.

Rats that were given natto extract showed an average decrease on blood pressure after just two hours. The data showed an approximate 12.7 percent drop in systolic blood pressure.

Nattokinase is particularly potent because it enhances the body’s natural ability to fight blood clots in several different ways, said Dr. Milner.

“In some ways, nattokinase is actually superior to conventional clot-dissolving drugs,” said Dr. Milner. “T-PAs [tissue plasminogen activators] like urokinase [the drug], are only effective when taken intravenously and often fail simply because a stroke or heart-attack victim’s arteries have been hardened beyond the point where they can be treated by any other clot-dissolving agent. Nattokinase, however, can help prevent that hardening.”


A team of researchers decided to use nattokinase in a case study to treat a retinal vein occlusion. In other words, the blood vessels draining out of the eye of a fifty-eight-year-old man were blocked by a blood clot. The blockage had caused bleeding in the eye and swelling from the backed-up blood, resulting in tiny vessels bursting. Using natto as the source of nattokinase, researchers fed the man a 100-gram serving before going to bed every night. Ten days later, the bleeding from the bottom of his eye was stopped. And at twenty days, the man’s vision was recovered and he was sent home from the hospital with instructions to continue to eat natto twice a week. In the space of two months, the nattokinase had completely dissolved the occlusion.


Recent research indicates that the body’s natural response to an injury by blood clots to arterial walls is to build up cholesterol in arterial plaques. Hence, if nattokinase can prevent blood clots from forming in the blood, then heightened cholesterol levels could be avoided.


Certain types of diabetes have also been shown to be due to changes in the blood vessels supplying the pancreas, again tied to small blood clots in these vessels.


As mentioned earlier, natto is the original form and source of nattokinase. However, thanks to modern technology, nattokinase is available in capsule form. A wide range and variety is currently available, including a highly advanced supplement that contains no soy and no vitamin K.

The standard dosage recommendations are 2,000 FU (fibrin units—or 50 grams) daily for a preventative, and 4,000 to 6,000 FU (160 to 200 grams) daily for therapeutic use.

For those using nattokinase for therapeutic purposes, it’s important to use a high-quality, researched nattokinase enzyme standardized for potency and guaranteed to be free of vitamin K to prevent bleeding side effects and contraindications.


Natto is considered a safe traditional food when eaten in moderate amounts. However, nattokinase enzyme and extracts that naturally contain vitamin K can interfere with blood-thinning drugs like coumadin and aspirin. Therefore, patients who are currently on blood thinners and those who suffer from kidney or liver disease should consult their doctor before using nattokinase.

People with bleeding disorders, such as hemophilia or a group of diseases called hemorrhagic diathesias, should not take nattokinase. People with ongoing bleeding problems, including ulcers, recent surgery, or recent major trauma should also avoid taking nattokinase.

Pregnant or nursing women should consult their doctors before using nattokinase until additional research confirms its safety.


Though it’s stinky and slimy in its natural state, the fermented soy product nattokinase has demonstrated some pretty remarkable health-promoting qualities in clinical research. Chief among them is nattokinase’s ability to improve circulatory health through its blood-thinning and anticlotting properties. With heart disease and stroke the first and third most common killers in the United States, nattokinase may prove to be a significant addition to the arsenal of disease-preventing supplements now available at your local health food store.


Amano Enzyme, Inc. “Natto—Traditional Japanese Fermented Soy Beans with Recently Discovered Health Benefits and Novel Industrial Applications.” Enzyme Wave 3, June 2002, 2–4.

Coumadin toxicity, information on: see

Maruyama M., Sumi H. “Effect of Natto Diet on Blood Pressure.” JTTAS, 1995.

“National Healthcare Quality Report,” AHRQ, U.S. Department of Health and Human Services, 2003.

Sumi H., Hamada H., et al. “A novel fibrinolytic enzyme (nattokinase) in the vegetable cheese Natto; a typical and popular soybean food in the Japanese diet.” Cellular and Molecular Life Sciences. 1987; 43 (10): 1110–11.

Sumi H., Hamada H., et al. “Enhancement of the fibrinolytic activity in plasma by oral administration of nattokinase.” Acta Haematologica. 1990; 84 (3): 139–43.

Suzuki Y., Kondo, K., et al. “Dietary supplementation with fermented soybeans suppresses intimal thickening.” Nutrition. 2003 Mar; 19 (3): 261–64.



Vitamin D is a fat-soluble vitamin that the human body uses to maintain normal calcium metabolism and promote bone health. The body can synthesize vitamin D when the skin is exposed to ultraviolet radiation from the sun. Additionally, vitamin D can be obtained from both natural food sources and fortified foods. Vitamin D deficiency can create a range of health problems, and a severe deficiency results in a condition known as rickets, a debilitating decalcification of the bones that was common among American children until the 1940s, when the U.S. government began a widespread program to fortify milk.

Today, a slew of important new studies has renewed interest in the role vitamin D plays in maintaining health and preventing disease. In fact, solid scientific evidence associates vitamin D deficiency with an increased incidence of many diseases—including cancer, cardiovascular disease, osteoporosis, stroke, Parkinson’s disease, and autoimmune disorders—and suggests that supplemental vitamin D can help prevent these serious health conditions.

New discoveries about vitamin D’s role in human health have been so important that Time magazine named “The Benefits of Vitamin D” one of the top ten medical breakthroughs of 2007. Adding his perspective to the excitement, interventional nutrition expert Dr. Greg Plotnikoff doesn’t mince words: “Because vitamin D is so cheap and so clearly reduces all-cause mortality, I can say this with great certainty: Vitamin D represents the single most cost-effective medical intervention in the United States.”


Vitamin D plays a critical role in many physiological processes, including calcium balance, blood pressure regulation, insulin production, cell differentiation, and immune system function. Vitamin D’s most important function involves maintaining normal blood levels of calcium, assisting in the absorption of calcium, and building bone mass.


Vitamin D is available from three basic sources: sunlight, food, and supplements. Most people depend on a combination of these sources to meet their nutritional needs.


Exposure to sunlight stimulates the epidermis of the skin to produce vitamin D. In fact, many people meet their entire vitamin D requirement by exposure to the sun. However, people with dark skin and those with limited exposure to sunlight need to be especially careful to ensure that their vitamin D needs are met through diet or supplementation.


While most vitamins are naturally prevalent in many of the foods we eat, food sources of vitamin D are quite limited. The best food sources are egg yolks and oily fish such as salmon, mackerel, and sardines. Foods with small amounts of vitamin D include oatmeal, parsley, sweet potatoes, and dandelion greens.


Because natural food sources of vitamin D are so limited, food manufacturers routinely fortify processed foods with the vitamin. The U.S. government initiated fortification in response to the high incidence of rickets among children in the first half of the twentieth century. In fact, in the 1920s, 75 percent of children in New York Public Schools had some form of rickets. In the 1940s, U.S. dairies began fortifying milk with vitamin D, which led to drastic reductions in the incidence of rickets in the U.S. population.

Today, the foods most commonly fortified with vitamin D include milk, orange juice, yogurt, and ready-to-eat breakfast cereals. Eight ounces of milk or fortified orange juice contain 100 IU of vitamin D, and a one-cup serving of fortified breakfast cereal contains 40 to 50 IU. Not all breakfast cereals or brands of orange juice are fortified with vitamin D, so it’s important to read the labels to determine exact vitamin D content.


Vitamin D is also available in supplement form, either as part of multivitamin formulas or as an individual supplement. Taking a vitamin D supplement is the easiest and most effective way to ensure an adequate intake of vitamin D.



Nutritionists once based recommendations for daily vitamin D intake solely on the amount needed to prevent rickets. But because scientists now recognize vitamin D’s role in so many critical physiological functions, experts now recommend 200 IU for adults under 50, 400 IU for adults ages 51 to 70, and 600 IU for adults over 70.


In 2008, the American Academy of Pediatrics (AAP) revised its recommended daily intake of vitamin D for infants and children to 400 IU. Additionally, the AAP recommends vitamin D supplements for breast-fed and partially breast-fed infants as well as non-breast-fed infants and children who drink less than one liter of vitamin-D–fortified milk or formula per day.



Symptoms of vitamin D deficiency include muscle pain, muscle twitching, visual problems, bone pain, anemia, diarrhea, joint pain, insomnia, nervousness, and a burning sensation in the mouth. If you have any of these symptoms and suspect a deficiency, consult with your physician for proper diagnosis and treatment.


Several population groups in the United States are at particular risk for vitamin D deficiency. These groups fall broadly into several categories, including people with limited sun exposure, the elderly, people with certain health conditions, exclusively breast-fed infants, and people taking certain medications.


As we age, our ability to synthesize vitamin D from sunlight decreases, resulting in lower vitamin D levels. Additionally, the elderly are more likely to spend time indoors and out of the sun. For older adults, the benefits of supplemental vitamin D in preventing disease and prolonging life are especially important.


Several health conditions can affect the absorption and metabolism of vitamin D. People with these conditions should consult with their physician to determine appropriate supplementation strategies. These conditions include:

• Obesity

• Fat malabsorption syndromes, including cystic fibrosis and cholestatic liver disease

• Inflammatory bowel disease and Crohn’s disease


Human milk contains only 25 IU of vitamin D per liter, so exclusively breast-fed infants need supplemental vitamin D to reach the recommended daily intake of 400 IU.


Certain medications can interfere with vitamin D absorption. These medications include barbiturates, corticosteroids, antacids, and statins (cholesterol-lowering drugs). People taking these medications should consider vitamin D supplementation to ensure sufficient intake.


An important study published in the Archives of Internal Medicine in 2008 reveals that inadequate vitamin D intake significantly increases overall mortality. In the study, Johns Hopkins University researchers followed a group of 13,000 initially healthy men and women for more than eight years. During this period, 1,806 people died, including 400 who were deficient in vitamin D. Lead author Dr. Michal Melamed summarized the study’s results: “Those who had the lowest levels of vitamin D had a 26 percent higher risk of death from all causes compared to those with the highest vitamin D levels.”


Scientists have long recognized the importance of vitamin D in human health, but recent studies have forced the medical world to reevaluate the role vitamin D plays in preventing disease. Dr. Michael F. Holick, director of the Vitamin D, Skin and Bone Research Laboratory at Boston University Medical Center, said, “We know that being vitamin D sufficient reduces the risk of having your first heart attack by more than 50 percent, reduces the risk of having peripheral vascular disease by as much as 80 percent, and decreases the risk of prostate, colon, breast and a whole host of other cancers by as much as 50 to 70 percent.”


Vitamin D deficiency can contribute to the development of osteoporosis. A 2006 multinational study of 2,600 postmenopausal women with osteoporosis found that 64 percent of the participants had insufficient blood levels of vitamin D. Additionally, in a 2003 study published in the American Journal of Clinical Nutrition, researchers followed 72,000 women for 18 years and found that the women who consumed at least 600 IU per day of vitamin D had a 37 percent lower risk of osteoporosis-related hip fracture than women who consumed less than 140 IU per day. Other clinical trials offer additional evidence that vitamin D supplementation reduces bone density loss and osteoporotic fractures in adults who are deficient.

Current evidence suggests that a minimum daily intake of 600 IU of vitamin Dcan reduce the incidence of bone decalcification and fractures among the elderly. Those who take supplemental vitamin D to promote bone health and avoid fractures should also ensure an adequate dietary intake of calcium (1,000 to 1,200 mg per day).


Scientists have found positive links between vitamin D deficiency and several types of cancer, including breast cancer, prostate cancer, and colon cancer. A 2007 study of 1,200 postmenopausal women revealed that participants who took supplements containing 1,100 IU of vitamin D and 1,400 mg of calcium over a period of four years had an overall cancer rate that was 60 percent lower than participants who took only placebos. Study leader Joan Lappe of Creighton University summarized the results: “This clinical trial strongly supports the observational studies that have associated sunlight and vitamin D levels with a lower risk of cancer.”


Several recent studies offer strong evidence that low vitamin D levels are correlated with the incidence of cardiovascular disease. In a 2008 study published in the Archives of Internal Medicine, researchers compared 454 men aged 40 to 75 who had a history of heart disease with 900 men who had no history of heart disease. Researchers found that participants with deficient vitamin D levels had a higher risk of heart attack than those with higher vitamin D levels. In another study—one of the most important to date—researchers followed 1,739 members of the Framingham Offspring Study for five years and found that the incidence of cardiovascular disease—including heart attacks, heart failure, and strokes—was from 53 to 80 percent higher in people with low blood levels of vitamin D.


According to the American Heart Association, over half a million Americans have a stroke each year. The most common risk factors for stroke include smoking, high blood pressure, lack of exercise, and heart disease. But a study of 6,000 people conducted in Heidelberg, Germany, suggests that the incidence of stroke is higher among people with low vitamin D levels, indicating a correlation between low vitamin D levels and stroke. In another study, a Cambridge University neurologist compared blood vitamin D levels of 34 stroke patients with those of 96 healthy volunteers. Results show that the stroke patients’ blood vitamin D levels were a third lower than those of the healthy volunteers.


Parkinson’s disease is a serious, debilitating health condition that causes stiffness, tremors, and slowness of movement due to inadequate levels of dopamine in the brain. In a 2008 study, researchers at the Emory University School of Medicine found that low vitamin D levels may be associated with Parkinson’s disease. In the study, researchers found that 55 percent of Parkinson’s patients had insufficient vitamin D levels, compared with 36 percent in a group of healthy elderly participants. Lead researcher Marian Evatt, MD, summarized the results: “We found that vitamin D insufficiency may have a unique association with Parkinson’s, which is intriguing and warrants further investigation.”


Autoimmune diseases (such as rheumatoid arthritis, multiple sclerosis, and type 1 diabetes) occur when the body launches an immune attack against its own tissues. Researchers have found that one type of immune cell, T cells, are responsible for mediating immune response, and that vitamin D is an important modulator of immune response, thus potentially diminishing the severity of autoimmune diseases. Animal studies confirm that vitamin D therapy can be beneficial in cases of rheumatoid arthritis, type 1 diabetes, and multiple sclerosis.


According to the American Dietetic Association, the daily tolerable upper intake level of vitamin D for children and adults is 2,000 IU. To prevent vitamin D toxicity and any long-term damage it may cause, do not exceed the 2,000 IU daily limit. Additionally, people who eat large quantities of fish or drink large amounts of fortified milk should use caution when taking supplemental vitamin D.

Long-term, excessive vitamin D intake can lead to serious health conditions, including bone loss; calcification of the heart, lungs, and kidneys; and deafness due to calcification of the tympanic membrane of the ear.

Possible symptoms of vitamin D toxicity include nausea, excessive thirst, appetite loss, dizziness, and headaches. If you think you may be suffering from vitamin D toxicity, please see your physician. In addition, individuals with gout, rheumatoid arthritis, and hyperthyroidism should consult with their physician before taking more than 400 IU per day.


To avoid any possible drug interactions, please talk with your physician before taking a vitamin D supplement with any of the following medications: orlistat (Xenical), cholestyramine (Questran), ketoconazole, and colestipol (Colestid).


Compston, J.E. “Vitamin D deficiency: time for action: Evidence supports routine supplementation for elderly people and others at risk.” British Medical Journal. 1998;317:1466–67.

“Doctors double vitamin D for children.” Boston Accessed 3:30 p.m., November 11, 2008.

Fragakis, Allison, Thomson, Cynthia. The Health Professional’s Guide to Popular Dietary Supplements. Chicago: American Dietetic Association, 2007.

Holick, M.F., Shao, Q., et al. “The vitamin D content of fortified milk and infant formula.” New England Journal of Medicine. 1992;326:1178–81.

“Lack of Vitamin D Boosts Death Risk.” U.S. News & World Report. August 11, 2008.

Melamed, Michal, Michos, Erin, et al. “25-Hydroxyvitamin D Levels and the Risk of Mortality in the General Population.” Archives of Internal Medicine. 2008;168(15):1629–37.

Pedersen, Stephanie. Vitamin D: Making the Most of Minerals. New York: Dorling Kindersly, 2000.

Reid, I.R. “The roles of calcium and vitamin D in the prevention of osteoporosis.” Endocrinology Metabolism Clinics of North America. 1998;27:389–398.

“Top 10 Medical Breakthroughs 2007.” Time.,30583,1686204_1686252_1690393,00.html Accessed 9:50 a.m., November 10, 2008.

Wagner, Carol L., Greer, Frank R., et al. “Prevention of Rickets and Vitamin D Deficiency in Infants, Children, and Adults.” American Academy of Pediatrics.;122/5/1142.pdf Accessed 11:20 a.m., November 10, 2008.

“Vitamin D.” Linus Pauling Institute, Oregon State University. Accessed 4:00 p.m., November 12, 2008.

“Vitamin D nears superstar status, as few get enough.” Accessed 10:15 a.m., November 11, 2008.

“Vitamin D supplementation.” Centers for Disease Control. Accessed 9:20 a.m., November 7, 2008.



Vitamin K is a fat-soluble vitamin that the body uses for blood clotting and bone formation. The “K” in vitamin K comes from the German word koagulation, because the vitamin is essential for the synthesis of proteins that are required for blood coagulation. There are three different forms of vitamin K: Vitamin K1 (phylloquinone), which is found in plant foods containing chlorophyll; Vitamin K2 (menaquinone), which is found in animal foods and is also synthesized by bacteria in the human gut; and vitamin K3 (menadione), a synthetic form that is not found in nature. Vitamins K1 and K2 both have roles as dietary supplements in recommended amounts, but vitamin K3 is not used as a dietary supplement.


Good food sources of vitamin K include dark leafy greens, such as spinach, broccoli, and kale, and vegetable oils, such as canola oil, soybean oil, olive oil, and cottonseed oil. Additionally, some fruits, nuts, and vegetables contain small amounts. One cup of dark leafy greens provides about 120 micrograms of vitamin K, the recommended daily intake for adult men. Most multivitamins contain the recommended daily amount of vitamin K, and further supplementation is typically not needed. However, vitamin K1 (phylloquinone) and K2 (menaquinone) supplements are available at health food stores and are useful in cases of specific health conditions.


The American Dietetic Association recommends a daily intake of 75 micrograms for teenagers aged 14 to 18, 90 micrograms for women, and 120 micrograms for men. Most people’s vitamin K needs are easily met through diet alone. Individuals taking anticoagulants (blood-thinning drugs) should be careful to eat vitamin K–rich foods in moderation, as too much vitamin K can interfere with the action of their medication.


Although vitamin K deficiency is rare in the United States, a true deficiency interferes with blood clotting. Symptoms of deficiency include various types of excessive bleeding, such as blood in the urine, nosebleeds, bleeding gums, heavy menstrual bleeding, or tarry, black stools. If you suspect you may be suffering from a vitamin K deficiency, please consult with your physician for proper diagnosis and treatment.


The American Academy of Pediatrics recommended in 1961 that all newborn babies receive an injection of vitamin K to prevent hemorrhagic disease, a condition that interferes with blood coagulation. Since infants are born with a sterile intestinal tract, and a major source of vitamin K is gut bacteria, it takes some time until infants’ gut bacteria can colonize and produce adequate levels of vitamin K. The practice of vitamin K supplementation at birth has dramatically reduced the incidence of hemorrhagic disease among infants in the United States.


Scientists refer to the process of blood clotting as the coagulation cascade, a series of interdependent events that stop bleeding though the formation of clots. The body utilizes seven different clotting factors, or proteins, in the coagulation cascade, and vitamin K is required to activate these seven factors. If the body lacks adequate amounts of vitamin K to activate the seven clotting factors, blood clots cannot form, leading to life-threatening bleeding disorders.


Preliminary research suggests that inadequate vitamin K intake may be correlated with an increased incidence of aortic calcification, leading to the development of arteriosclerosis. In a population-based study published in the journal Atherosclerosis in 1995, researchers followed 256 postmenopausal women and found an inverse correlation between long-term intake of vitamin K and arterosclerotic aorta calcification; in other words, the women with lower vitamin-K levels had more aortic calcification than those with higher levels.

In a 2004 study, Dr. J.M. Gelejinse and colleagues also found a significant inverse correlation between long-term, inadequate vitamin K2 intake and aortic calcification. While additional research needs to be done, it looks like maintaining adequate vitamin K levels can help prevent arteriosclerosis and the serious cardiovascular events it can precipitate.


Scientists are increasingly recognizing the critical role that vitamin K plays in building strong bones and maintaining bone health. In fact, three proteins that the body uses to form bone tissue—osteocalcin, anticoagulant protein S, and matrix gla protein—cannot be activated without sufficient blood levels of vitamin K. Specifically, vitamin K assists in deposition of calcium, magnesium, and phosphorus in the bone matrix. Studies have shown that elderly people with low vitamin K intake have suboptimal bone density and are at increased risk of osteoporosis. Additional evidence from several important clinical trials reveals that vitamin K supplementation—in cases of deficiency—can decrease loss of bone density and overall fracture rates. A 1998 study of postmenopausal women who ate one or more servings of lettuce a day (lettuce is a good source of vitamin K) were 45 percent less to have hip fracture likely than women who ate one serving or less of lettuce per week.

Another study compared the effects of vitamin K2 on bone mineral density to the effects of estrogen replacement therapy and vitamin D3 supplementation. Researchers divided 72 healthy postmenopausal women into four groups. Women in each group received one of four treatments: a placebo; a vitamin D supplement; hormone replacement therapy; or 45 milligrams per day of supplemental vitamin K2. At baseline and after six and 12 months of treatment, scientists measured bone mineral density in all four groups. They found that the women in the vitamin K and vitamin D groups had significantly less bone loss than the women in the placebo and hormone replacement therapy groups.


Nutrition experts consider vitamin K to be safe at recommended dosages. No tolerable upper intake level has been set, and vitamin K deficiencies are quite rare. Because vitamin K is a fat-soluble vitamin, consumption above the recommended daily intake levels is not recommended and may cause toxicity.


Individuals who are taking aspirin, antibiotics, anticoagulant/antiplatelet drugs, doxorubicin, laxatives, high doses of vitamin E, weight-loss medications, or warfarin (Coumadin) should consult with their physician before taking vitamin K supplements. Additionally, anyone on a daily aspirin regimen to help prevent cardiovascular disease should check with a health care professional before taking vitamin K supplements.


Booth S.L., Sokoll L.J., et al. “Assessment of dietary phylloquinone intake and vitamin K status in postmenopausal women.” European Journal of Clinical Nutrition. 1995 Nov;49(11):832–41.

Booth S.L., Suttie J.W. “Dietary intake and adequacy of vitamin K.” Journal of Nutrition. 1998 May;128(5):785–88.

Braam L.A., Knapen M.H., et al. “Vitamin K1 supplementation retards bone loss in postmenopausal women between 50 and 60 years of age.” Calcified Tissue International. 2003;73:21–26.

Geleijnse J.M., Vermeer C., et al. “Beyond Deficiency: potential benefits of increased intakes of vitamin K for bone and vascular health.” European Journal of Nutrition. 43(6); Dec 2004, 325–35.

Hodges S.J., Pilkington M.J., et al. “Depressed levels of circulating menaquinones in patients with osteoporotic fractures of the spine and femoral neck.” Bone. 1991;12(6):387­–89.

Jie K.S., Bots M.L., et al. “Vitamin K intake and osteocalcin levels in women with and without aortic atherosclerosis: a population-based study.” Atherosclerosis. 1995 Jul;116(1):117–23.

Kawashima H., Nakajima Y., et al. “Effects of vitamin K2 (menatetrenone) on atherosclerosis and blood coagulation in hypercholesterolemic rabbits.” Japanese Journal of Pharmacology. 1997 Oct;75(2):135–43.

Meunier P.J. “Calcium, vitamin D, and vitamin K in the prevention of fractures due to osteoporosis.” Osteoporosis International. 1999;9(Suppl 2):S48–52.

Weber, P. “Vitamin K and bone health.” Nutrition. 2110;17:880–87.