DEAR DR. BLONZ: I have begun taking statins for my elevated cholesterol. I've been advised to stop drinking grapefruit juice and eating grapefruit, because it impedes the body's ability to get rid of statins (and other medications). I enjoy grapefruit and am a bit disappointed, but certainly do not want to do anything to counteract a medication my body needs. Can you provide a brief explanation? -- S.T., San Jose, California
DEAR S.T.: Medications are given for a reason, but from the body's perspective, they are foreign substances that need to be eliminated. The body can rid itself of unwanted substances through the kidneys, the digestive tract, via breath exhalations, or even through the skin.
In many cases, medications or other "undesirable" compounds will first be broken down, or metabolized, by special enzymes prior to disposal. (Think of this as similar to the way that foods are taken apart by digestive enzymes before they can be absorbed.) The body uses various enzymes in its disposal system, but one of the stars is called cytochrome P-450 3A4, or CYP3A4 for short. This enzyme is present in the liver -- the organ that does the lion's share of the breakdown work. CYP3A4 is also present in the walls of our digestive tract.
The point of all this is that the partial breakdown of medication before absorption is normal and expected, as is the breakdown by the liver. These factors are all studied and accounted for when arriving at a drug's therapeutic dose. But grapefruit juice acts as a wild card because it inhibits the ability of the CYP3A4 enzyme to do its job. This is not an interaction with the medication itself; if that were the case, the effect would be more short-lived, persisting until the next dose. Rather, it is analogous to sand in the gears of an enzyme "machine."
This interaction was uncovered in 1989 when a researcher used grapefruit juice to mask flavors in a study designed to test how alcohol affected a particular medication. The results were unexpected, and the scientists soon realized that grapefruit was more than a benign flavorant. Researchers soon began investigating the range of the "grapefruit effect."
When grapefruit juice is around, more of the drugs get absorbed because the breakdown in the walls of the intestines no longer takes place. Grapefruit affects the ability of this enzyme to break down the medication, which means that blood levels remain higher for a longer period of time. Depending on the medication, the grapefruit effect can be serious, and it can remain long after the fruit is consumed. In one study, the effect was significant 24 hours after grapefruit juice was consumed.
Grapefruit and its juice cause this issue with a wide range of medications -- all those that are normally metabolized by the CYP3A4 system. The list includes some cholesterol-lowering drugs, certain anticonvulsants, calcium-channel blockers (prescribed for heart disease), cyclosporin (used after transplants) and benzodiazepines. If you enjoy grapefruit juice and you are on prescription medications, it is essential that you check with your pharmacist or your physician to see if your medication is at risk. Read more about the grapefruit effect at tinyurl.com/j4l72nf.
Send questions to: "On Nutrition," Ed Blonz, c/o Universal Uclick, 1130 Walnut St., Kansas City, MO, 64106. Send email inquiries to email@example.com. Due to the volume of mail, personal replies cannot be provided.