Q: I have a friend who has a cholesterol problem but can’t take medication for it because of elevated liver enzymes. Her doctor told her to mix 4 cups of apple juice with 3 cups of white grape juice and 1/2 cup of apple cider vinegar. She is supposed to drink 6 ounces of this mixture every morning.

She’s been following this regimen for approximately six months, and her cholesterol is going down. Could this drink lower cholesterol?

A: As far as we can tell, there aren’t any scientific studies to support the use of vinegar to lower cholesterol. Despite the lack of evidence, we often hear from readers that apple cider vinegar has health benefits. One woman reports:

“I am 44 years old with four grown children and four grandchildren. I take apple cider vinegar every day. My recent physical showed my HDL (good cholesterol) is 63 and my bad LDL cholesterol is 61. My husband was astonished, since before I started taking apple cider vinegar my total cholesterol was 384. I also eat lots of garlic, drink green tea and eat tons of vegetables.”

Q: I learned about the so-called “Mayo diet” and have been following it with good results. This diet calls for eating half a grapefruit three times a day. I also drink two glasses of grapefruit juice.

Someone at work mentioned that grapefruit can interact with certain medications. I take prescription pills for high blood pressure and high cholesterol. Will this be a problem?

Also, I had kidney stones last fall and recently heard that grapefruit juice could be involved. Is this true?

A: Your diet is not endorsed by the Mayo Clinic. As the clinic’s Web site notes: “None of these ‘magic’ diets that push grapefruit or eggs or promise to peel off pounds are approved by Mayo Clinic  and can be dangerous for some individuals.”

Grapefruit juice is a great source of nutrients, but a study published in the Annals of Internal Medicine (Dec. 1, 1998) suggested that regular intake of grapefruit juice might increase the risk of kidney stones. Varying your juice choices would probably be wise.

Grapefruit does interact with many kinds of medicines, including certain blood pressure and cholesterol-lowering drugs.

We are sending you our newly revised “Guide to Grapefruit Interactions.” Others who would like a copy should send $2 in check or money order with a long (No. 10), stamped, self-addressed envelope to: Graedons’ People’s Pharmacy, No. J-91, P.O. Box 52027, Durham, N.C. 27717-2027.