Warfarin and Supplement Interactions – and What About Food?

Way back in 1988 I was Editor of a book called The Medicine Chest which was a straightforward examination of the interactions between drugs, supplements and foods. It had a lot of good advice that hasn’t changed much over the years so I was surprised to receive a ‘news’ item that warned that Warfarin when taken with vitamin E and large doses of vitamin C can decrease effect of the drug.

I was not surprised at the effect because I was writing about it over 20 years ago, but that it was news came as a surprise. However, it never hurts to repeat a good piece of information and scientists never turn up a chance for a grant to research something we already know.

This time it is researchers at the Intermountain Medical Center Heart Institute in Salt Lake City, Utah who want to point out the dangers. Warfarin is a commonly prescribed drug used to prevent blood clots from forming and given to people with certain types of irregular heartbeat, those with prosthetic heart valves, and those who have suffered a heart attack.

The study consisted of interviews with 100 atrial fibrillation patients to determine their understanding of potential interactions between supplements and medications such as Warfarin. This is not really a study about interactions but of people’s understanding of them and generally people do not know enough about how supplements, and everyday foodstuffs react with their medication.

In this study more than half were unaware of potential interactions and they also found that of the 100 most-used supplements (vitamins, glucosamine/chondroitin, fish oil and coenzyme Q10) 69 percent interfere with the Warfarin’s effectiveness.

Warfarin and herbal and dietary supplements “compete” in the liver and this competition changes the way the blood thinner works — either intensifying its active ingredients, thereby increasing the risk of bleeding, or by reducing its effectiveness, increasing the risk of stroke.

All true, and the lead researcher is urging that doctors do a better job of teaching patients about the dangers of mixing Warfarin with these products. Now I entirely agree with him, but what he doesn’t mention is that this particular drug is also seriously affected by certain foodstuffs and other drugs.

Given what the average doctor knows about nutrition I hold out little hope they will also pass on this advice so that instead of increasing or decreasing their drug prescription they could suggest changes to their patients diet. In addition, the effectiveness of Warfarin is impacted by other drugs – particularly antifungals, barbiturates and beta blockers which all decrease the drugs effectiveness.
Conversely, antibiotics, some diabetes drugs, gout medicines, tricyclic antidepressants and asprin and paracetamol – among others – all can increase the drug’s effectiveness, making it more potent.

On Warfarin? Avoid These:
Warfarin is affected by large doses of vitamin E, vitamin C, bioflavanoids and calcium and a large intake of fats or oils. If the diet is also high in vitamin K rich foods this can cause an imbalance in the body which could decrease the anticoagulant effect.

Vitamin K is needed to allow your blood to clot normally, to protect your bones from fracture and postmenopausal bone loss, to prevent calcification of the arteries and provide possible protection against liver and prostate cancer.

Vitamin K is a fat soluble vitamin and only a small amount is able to be stored in the body. It is destroyed by light and acids and alkalis such as vinegar or baking soda. A deficiency of it can lead to increased blood clotting time, easy bruising and excessive bleeding.

Significant food sources include: green leafy vegetables including spinach, Brussels sprouts, Swiss chard, green beans, asparagus, broccoli, kale and also cauliflower, cow’s milk, eggs, fish liver oils, green vegetables, kelp, liver, molasses, polyunsaturated oils, tomatoes

Everyone responds differently to drugs, foods and supplements so if you have any concerns, or if your diet is high in vitamin K rich foods, then you should discuss with your doctor how this is affecting your medication.

Varicose Veins Linked to DVT

October 27, 2009 by  
Filed under Medical Research & Studies, Travel


Varicose veins are generally harmless, though not considered attractive, but a new study in Graz, Austria reveals that danger may be lurking under your skin.

There are any number of reasons to get varicose veins including family history, jobs where you are standing for long periods such as hairdressers and teachers, being very overweight and of course in pregnancy.   The most common form generally seen is superficial vein thrombosis (SVT), where the veins become inflamed and swollen.  It can be a painful condition, but most doctors don’t regard it as a major problem.
However this new research looked at a potential link between varicose veins and DVT (deep vein thrombosis) which a dangerous condition that prompts blood clotting in the legs.  Clots that break away can cause thromboembolism (restricted blood flow), and even death if the clot reaches the lungs and triggers a pulmonary embolism.

Of the 50 patients examined who had confirmed SVT it was found that one in four of them had DVT, although none had shown any symptoms.   This suggests those with varicose veins need to be alert and ask for a sonagraph screening to establish if they are at risk.

Varicose veins and Vitamin K link
One factor in keeping your veins healthy is to have a good intake of vitamin K as its importance for circulatory health is already well known.
There was an important study done in France in 2007, only on male subjects, with and without varicose veins. They found a link between getting varicose veins and low levels or no activity of a protein called matrix GLA protein.  This protein is only properly activated when vitamin K levels are adequate, so the researchers at Nantes University concluded that a dood intake of the vitamin may play a role in varicose vein prevention.

If you have any history of narrowing of the arteries in your family, then some nutritionists 5 to 15 mg of vitamin K per day, but that is considerably higher than the recommended daily allowance.
If you want to increase it in your diet then it’s mostly found in dark green leafy vegetables like spinach, brussel sprouts, broccoli and cauliflower, also in cheddar cheese and oats.

WARNING!!! Vitamin K needs to be carefully monitored if you are on blood thinning or anticoagulant drugs after a stroke or surgery and a limited intake is suggested.

Vitamin K, helps women fight heart disease

October 27, 2008 by  
Filed under Food & Nutrition, Womens Health

Hardening of the arteries is a major concern for many, particularly as they get older, but new research has good news for women – sorry chaps but it doesn’t help you much apparently. It’s just been reported in the journal Atherosclerosis, that women who have the highest levels of vitamin K2 have the greatest protection against hardening of the arteries.

The researchers examined the diets of women in their 60s and found that vitamin K2 reduced hardening of the arteries by as much as 20 percent and the more K2, the better. We tend to be encouraged to eat more of the K1 vitamins, which are found primarily in leafy green vegetables, as they have plenty of other health benefits but they don’t provide any K2. The best sources are cheese and milk products and some from meat. These of course can be sources of cholesterol and fats, so don’t switch your diet completely – remember everything in moderation is the very best health advice.

Warning on fruit juice and drug interactions

Sorry to be still on the fruit juice trail, but news this week had a real deja-vu quality about it for me. In the 1980′s, I was involved with a naturopath in the writing of a book called ‘The Medicine Chest’ which looked at the relationship and interaction between foods, vitamins and medicines. One of the things we flagged up then was how food can affect your medication. One example of this is the drug warfarin which interacts with vitamin K, which we get from food, and from the bacteria in our gut. Vitamin K is involved in the formation of special liver proteins, known as coagulation factors, which reduce the risk of haemorrhage or bleeding. Conversely, if you are susceptible to blood clotting, warfarin (because of how it interferes with the formation of these vitamin-K-dependent factors) may be prescribed for you. So you can see that if you increase the amount of vitamin K-rich foods then you can alter the effect that the warfarin will have in your body. Such foods include everyday items like spinach, lettuce, beef, broccoli and soy beans – good foods in themselves but to be discussed with your doctor if you are on warfarin.

Now the scientific world seems to have caught up with the research done by naturopaths over the years, which has always treated food as ‘medicine’ and been much more aware of its effects. Recent research presented at a US conference has now suggested that a chemical in grapefruit, orange, and possibly also apple juice, could stop anti-allergy drugs being absorbed properly. Grapefruit juice is already known to interfere with blood pressure drugs and indeed some medicines carry a warning that taking them alongside grapefruit juice could cause an overdose and normally your pharmacist will point this out to you. However, the latest finding shows that grapefruit juice had the reverse effect on fexofenadine, an antihistamine drug, making it less rather than more potent. Volunteers took the drug with either a single glass of grapefruit juice, or just water.

When it was taken with juice, only half the drug was absorbed, potentially reducing its effectiveness. The active ingredient of the juice, naringin, appears to block a mechanism which moves drug molecules out of the small intestine into the bloodstream and this substantially decreases the absorption of certain drugs.

The three juices mentioned have also been found to affect etoposide, a chemotherapy drug, some beta-blocker drugs used to treat high blood pressure, and cyclosporine, taken by transplant patients to prevent rejection of their new organs. Dr David Bailey of the University of Western Ontario, the study’s author, said: “This is just the tip of the iceberg – I’m sure we’ll find more and more drugs that are affected this way.”