Posted on August 8, 2007 by Joel Fuhrman, M.D.
From the September 2004 edition of Dr. Fuhrman's Healthy Times:
I have been asked by multiple individuals to give a complete answer
with guidelines for patients on Coumadin (Warfarin is the generic name)
who have been told by their health professionals to avoid green
vegetables because of the interaction between Coumadin and vitamin K.
This subject is of interest to me because I am a physician and author
who advocates a green vegetable-rich diet for both weight loss and
disease reversal and longevity. As a proponent of a diet rich in leafy
greens, broccoli, and other foods rich in vitamin K, my dietary
recommendations often contradict the advice of dietitians, nurses, and
doctors who advise their patients taking Coumadin to avoid vitamin
The reason health professionals recommend that their patients on
Coumadin avoid vitamin K containing foods is because Coumadin produces
its anticoagulation (blood thinning) effects by interfering with the
activation of a vitamin K-dependent enzyme that is needed to build
When you ingest more vitamin K from green vegetables, you can
decrease the effectiveness of Coumadin. A higher dose of the drug will
then be required to maintain the recommended degree of blood thinning.
The term “blood thinning” is a lay term that means a reduction in the
natural ability of the body to form a blood clot.
The following definitions are important in order to understand
Coagulation: refers to the formation of blood clots formed by
clotting factors and platelets, a normal body reaction when, for
example, you cut yourself. Coumadin (Warfarin) is called an
anticoagulant because it works against the formation of blood clots.
Thrombus/Thrombi: clots formed inside the blood vessels, typically to
seal a defect in the vessel wall. These clots, when formed in the blood
vessels that supply the heart with oxygen, cause heart attacks. Thrombus
is singular; thrombi is plural.
Embolus/Emboli: a traveling clot, usually caused by a thrombus that
breaks off and travels to a distal portion of the artery where it is
narrower, occluding it, leading to a stroke, pulmonary infarction, or
heart attack. A traveling thrombus is an embolus. Embolus is singular;
emboli is plural.
In many cases, Coumadin is used as a preventive treatment to reduce
the chance of forming emboli that could cause a stroke. Coumadin is most
often prescribed for patients with atrial fibrillation, a common
irregularity in the heart rate. When you have this irregular heartbeat,
the turbulent flow of blood increases the likelihood of the formation of
an embolus that can travel to the brain and cause a stroke. Coumadin
therapy also is used by people who have experienced a serious blood
Serious Side Effects
Since Coumadin is a drug given to prevent clots, the major side effect
is bleeding. When you are taking Coumadin, you will not stop bleeding
easily if you are cut. If you get in a car accident, you will more
likely bleed to death. If you have a stomach ulcer or a broken blood
vessel in your digestive tract while taking Coumadin, you can bleed to
The main problem with this medication is its very narrow therapeutic
range—too much, and you can suffer from a major bleeding episode; too
little, and it is ineffective at preventing embolic events. Patients
have to be closely monitored with blood tests and their dose adjusted
accordingly to make sure they are taking the correct amount.
According to current estimates, 70 percent of patients on Coumadin
tend to stop taking the medicine because of frustration with blood
tests, dosage changes, and side effects. While Coumadin monitoring is a
medical necessity, many times the demands of heavy patient loads can
make it very challenging for busy physicians to follow patients as
closely as necessary.
Besides the risk of a major bleed, another serious but more
infrequent complication of Coumadin therapy is drug-induced limb
gangrene and skin necrosis. Other adverse reactions that occur
infrequently include white blood cell diseases, hair loss, allergic
reactions, diarrhea, dizziness, hepatitis and abnormal liver function,
skin rash, headache, nausea and/or vomiting, and itching.
Physicians treat patients with Coumadin primarily to decrease the
occurrence of thrombo embolism. They perceive that this risk has a
greater clinical impact than the risk of Coumadin induced bleeding.
However, only recently has the extent of the risks of bleeding been
thoroughly investigated. A recent meta-analysis that pooled data from 33
separate studies examined the bleeding rates of patients who received at
least three months of anticoagulation therapy. Major bleeding occurred
at a rate of 7.22 per 100 patient-years, and fatal bleeding occurred at
the rate of 1.3 per 100 patient-years.1 That means if 10 people were put
on Coumadin therapy for ten years each, seven out of the ten would have
suffered a bleeding event and one would have died from taking Coumadin.
Only for High-Risk Patients
Before 1990, Coumadin therapy for the prevention of stroke for those who
had atrial fibrillation was limited to those who also had additional
risk factors, such as rheumatic heart disease and prosthetic heart
In recent years, however, hundreds of thousands of patients with
atrial fibrillation, including those without significant accompanying
risk factors, have been placed on Coumadin to decrease the risk of
embolic stroke. Medical studies have shown that patients with atrial
fibrillation, who also have other risk factors for strokes, did have a
survival advantage and a reduced risk of strokes when Coumadin was
prescribed. The results were considerably better than those in high-risk
patients who only used aspirin, but not considerably better in patients
who had only atrial fibrillation and no other serious risk factors.
Younger patients with atrial fibrillation and those without cardiac
risk factors have not been demonstrated to have lived longer as a result
of taking Coumadin. Aspirin does just as well in this low-risk group
mainly because strokes are more infrequent.
The American College of Cardiology recommends aspirin, not Coumadin,
for those patients with atrial fibrillation who have a relatively low
risk for embolic stroke. That includes patients who do not have
diabetes, advanced atherosclerosis, poorly controlled blood pressure, an
enlarged heart, a recent embolic event, obesity, or who smoke. In other
words, it is standard practice that treatment with Coumadin be guided by
the risk of thromboembolic events and not be used for those patients at
relatively low risk.
Eat more healthfully and stop taking Coumadin. The main problem with
the studies that show that patients at risk of stroke benefit from
anticoagulation with Coumadin is that they tested mostly high-risk
patients on the typical disease-creating American diet, not low-risk
patients on a vegetable-heavy, plant-based diet. As one’s diet changes
to include more vegetation and less and less animal products and refined
foods, one’s cholesterol drops, one’s blood pressure typically
decreases, and one’s risk of a heart attack or embolic stroke plummets.
A high-nutrient, plant-based diet already has been demonstrated in
medical studies to have a powerful effect at decreasing the risk of
embolic stroke as well as heart attacks. In fact, in the Nurses Health
Study a mere 5 servings per day of fruits and vegetables reduced risk of
embolic stroke by 30 percent (and this is still a poor diet by my
standards). 2 Another study looking at the consumption of greens,
vegetables, and daily fruit consumption found a dramatic decrease in
stroke incidence (approaching 50 percent) when they compared high and
low fruit and vegetable consumption.3 My dietary recommendations,
extremely low in salt and offering the equivalent of more than 10
servings per day of stroke-protecting produce, have been demonstrated to
dramatically lower cholesterol and offer a much greater resistance to
both strokes and heart attacks than Coumadin therapy. For people
following my nutritional advice, the use of Coumadin becomes
ill-advised. The use of this dietary intervention quickly drops people
from a high-risk to a low-risk status. In most cases, Coumadin is no
Most people on Coumadin would be much safer if they ate an ideal diet
with lots of vitamin K containing greens; took an aspirin, EPA/DHA fatty
acids, and LDL protect daily; and stopped taking the Coumadin. The risk
of all causes of death would decrease precipitously. Eating right will
not cause you to bleed to death. Instead, it can save your life.
Natural anticoagulants to consider instead of Coumadin are tomato
juice, pomegranate juice, fish oil, vitamin E, horse chestnut seed
extract, and ginkgo biloba.
Is Coumadin the Only Hope?
For those who absolutely must take Coumadin, because of a recent
thrombotic event, the danger of not eating a healthful diet exceeds the
risk of increasing the Coumadin dose slightly to accommodate the
healthier diet. As long as the amount of greens you eat is consistent,
your doctor can adjust your Coumadin dose to accommodate it.
For the patient who must stay on Coumadin, the diet must be
consistent from day to day to avoid fluctuations in the effectiveness of
the drug. To keep the vitamin K amount constant, it is sensible to eat
one large raw salad a day and one serving of dark green vegetables such
as asparagus and string beans, but leave out the dark green leafy
vegetables, such as steamed kale, collards, and spinach. Adding some of
those to a soup is okay, however. The goal is to keep your vitamin K
level stable, so the amount of blood thinning does not swing into a
danger zone. A dangerous level of blood thinning can occur if the dose
of Coumadin is adjusted to a high vitamin K intake and then suddenly the
patient does not eat many vitamin K-containing foods for a few days. In
other words, the main goal is to eat the same amount of vitamin
K-containing foods every day.
In summary, the evidence indicates that both Coumadin and aspirin are
effective for prevention of emboli in patients with atrial fibrillation.
Coumadin is more effective than aspirin in those very high-risk
patients, but is associated with a higher rate of serious bleeding. The
advice of the typical healthcare provider to severely limit vitamin
K-containing foods does not consider the risk reduction that occurs from
the dietary improvements. A diet high in processed foods and animal
products, although low in vitamin K, will increase your risk of a heart
attack and stroke. Instead, eat even more of those high-vitamin K foods
and, if at all possible, get off the Coumadin.
1. Linkins LA, et al. Clinical impact of bleeding in patients taking
oral anticoagulant therapy for venous thromboembolism. Ann Intern Med
2. Joshipura KJ, Ascherio A, Manson JE, et al. Fruit and vegetable
intake in relation to risk of ischemic stroke. JAMA 1999;282(13):1233-9.
3. Sauvaget C, Nagano J, Allen N, Kodama K. Vegetable and fruit
intake and stroke mortality in the Hiroshima/Nagasaki Life Span Study.
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