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Health Briefs

Even good foods can be bad for certain drugs

Some foods that otherwise would fall firmly into the "good for you" category – grapefruit, spinach and other dark, leafy vegetables – can be quite bad for you if you're taking certain drugs.

Those foods can cause a chemical reaction that can block the absorption of certain drugs and amplify or decrease the effectiveness of others. The drugs most likely to be affected include commonly prescribed blood pressure medications, anti-depressants and blood thinners.

"These foods interfere with the drug metabolism. They can allow the drug to be absorbed too quickly, or not at all, or not enough," says Dr. Christine Gerbstadt, who is also a registered dietician with the Chicago-based Academy of Nutrition and Dietetics.

A long list

According to research published in the November 2012 issue of the Canadian Medical Association Journal, 85 drugs can be adversely affected by grapefruit. In about half of those cases, the side effect can be severe, including blood clots, kidney damage, and muscle damage. Other citrus fruits, such as the oranges used in marmalade, also contain the "furanocoumarins" that impact the absorption of drugs. And, the journal noted, the reaction can be pronounced in patients over age 70 who take felodipine for high blood pressure.

For patients who take anti-coagulant medications such as warfarin (brand name: Coumadin),  the good food that turns bad is dark green leafy vegetables such as broccoli, kale, and spinach, which pack a dose of Vitamin K. Also found in certain oils, Vitamin K can thin blood, amplifying the effects of warfarin.

"It's not that we want people to stop eating foods that are good for them," says Judith Kolish, a registered dietitian who works for Health Care Service Corp., the parent company of the Blue Cross and Blue Shield plans in Illinois, New Mexico, Oklahoma, Texas, and Montana. "It's more that we want people to be consistent and eat the same amount each day" so doctors can adjust the drug dosage accordingly.

How to avoid reactions

What should you do if you take medications and are worried about the potential for food interactions? Start by talking to your medical professionals—your doctor and your pharmacist. Ask them about foods you should avoid in addition to over-the-counter medications such as pain killers and dietary supplements like multi-vitamins that might interact with your medications. If you still have the pamphlet that came with your medication, take the time to read it carefully.

You also can visit the Internet in search of additional information, but Gerbstadt warns, it's important to know that you are visiting sites that can be trusted to provide accurate medical information, such as MayoClinic.com.

Learn more about antioxidants and why they are good for you.