Doctors and pharmacists have known for nearly two decades that grapefruit juice can boost the body's absorption of certain prescription medications to a dangerous degree. In some cases, the tart and tangy beverage can cause normal drug doses to behave like toxic overdoses in the body.

Medications known to be affected in this way by grapefruit juice include many that are used in the treatment of high blood pressure, high cholesterol levels, cancer and those taken by organ transplant recipients to help prevent organ rejection. More than 50 medications are now known to interact unfavorably with grapefruit juice.

Earlier this month, researchers from the University of Western Ontario reported their most recent findings concerning drug-grapefruit interactions at the 236th National Meeting of the American Chemical Society. They demonstrated that the fruit juice can also have the opposite effect, substantially reducing the absorption of certain medications.

In a study of healthy volunteers, the Canadian scientists asked subjects to take fexofenadine, an antihistamine widely used in the treatment of allergies. Fexofenadine is sold under the brand name Allegra in the United States.

In the volunteers who took the drug with a single glass of grapefruit juice, only half the drug was absorbed compared to volunteers who washed down the medication with a glass of plain water. When less than the appropriate dose of a given drug is absorbed by the body, the scientists noted, its performance is likely to be negatively affected.

Previous research has shown that orange juice and apple juice may also reduce the absorption of certain medications, including antibiotics and several drugs commonly used in the treatment of heart disease and cancer.

Although grapefruit juice may not be the best chaser for prescription pills, it offers a bounty of benefits for healthy folks who are not taking grapefruit-sensitive medications. It's a tasty, refreshing drink that is completely fat free, and it has no cholesterol or refined sugar.

Grapefruit juice is packed with important vitamins and minerals. A single serving provides 100 percent of the recommended daily allowance for vitamin C, and it's an excellent source of folate, a B vitamin that helps prevent certain types of birth defects.

The juice is known to offer several important benefits for the heart and circulatory system. It's packed with antioxidants and other compounds that may reduce the risk of developing cardiovascular disease.

In a study conducted at the Hebrew University of Jerusalem, researchers demonstrated that eating a single serving of grapefruit daily brought about significant reductions in cholesterol levels in patients with heart disease. The study included 57 patients with high cholesterol levels who had recently undergone coronary bypass surgery and who had failed to respond sufficiently to cholesterol-lowering statin drugs.

After being assigned to one of three treatment groups, the patients were given either a single serving of red grapefruit, white grapefruit or no grapefruit along with regular, nutritious meals for 30 days. The patients who received either red or white grapefruit showed significant reductions in blood lipid levels, while those consuming the grapefruit-free diets showed no changes.

Red grapefruit was more effective than the white variety in lowering lipid levels, particularly levels of triglycerides in the blood. Elevated triglycerides are associated with a number of serious diseases, including heart disease and diabetes.

The impact of grapefruit juice on cancer risk is less clear. Although a 1996 animal study demonstrated a 50 percent reduction in breast tumor growth with the consumption of grapefruit juice, more recent studies yielded different results. In a study published last year in the British Journal of Cancer, researchers announced their findings that women who regularly consumed grapefruit had a 30 percent higher risk of developing breast cancer than women who ate none at all.

The study included more than 46,000 women and lasted for nearly 10 years. Drugs containing estrogen, a hormone responsible for fueling certain types of breast cancer, are known to interact unfavorably with grapefruit. At least two previous studies have found higher estrogen levels in women consuming grapefruit or grapefruit juice. The U.S. Food and Drug Administration requires hormone replacement products and many other medications to carry warning labels stating that grapefruit juice may increase drug concentrations in the body.

For most healthy individuals, drinking grapefruit juice is a great way to meet the minimum daily recommendation for fruit intake. But for folks taking prescription medications, it's wise to read all drug labels or check with a pharmacist before drinking up.

Rallie McAllister is a board-certified family physician, speaker and the author of several books, including "Healthy Lunchbox: The Working Mom's Guide to Keeping You and Your Kids Trim." Her website is www.rallieonhealth.com. To find out more about Rallie McAllister, M.D., and read features by other Creators Syndicate writers and cartoonists, visit the Creators Syndicate Web page at www.creators.com.

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