Q. Lately I've been hearing a lot about maca and how it can increase male sexual potency. Can you tell me what maca is, and if the claims are true?

A. Maca (Lepidium meyenii) is a plant from Peru that has been used for centuries to increase physical and sexual endurance. Cultivated in the harsh climate of the Andes, the plant only grows at elevations above 12,000 feet.

Modern research, including both animal and human testing, confirms long-held beliefs about maca's benefits. Although the exact mechanism by which it works has not been elucidated, the root of the plant — the part traditionally used to increase physical and sexual endurance — has been found to contain active compounds that may explain its effects.

Let's look at claims that have been made about maca, and see what studies have to say:

Maca increases sexual desire in men: A study in the journal Andrologia in 2002 found maca improved sexual desire in men ages 21 to 56 who took 1.5 to 3.0 grams for 12 weeks.

Maca increases male sexual potency: A study in the Asian Journal of Andrology in 2001 reported that 4 months of oral treatment with maca improved seminal fluid volume, sperm count, sperm motility and sperm mobility in men ages 32 to 44. The study also concluded that maca did not affect testosterone, estrogen, prolactin or pituitary hormones FSH and LH.

Maca doesn't affect hormones: A study published in the Journal of Endocrinology in 2003 found serum testosterone levels were unchanged in men who took 1.5 to 3.0 grams of maca for 12 weeks — good news for men concerned with preventing prostate enlargement.

Maca increases sexual behavior in animals: A study published in the Journal of Ethno-pharmocology in 2001 found that mice treated with maca extracts had significant improvements in sexual behavior.

Maca helps you cope with stress: In addition to increasing male sexual potency, maca has stress-relieving effects. A study published in Phytotherapy Research in June 2004 found that maca has "adaptogenic" properties — which means that it helps the body adapt, or better cope, with stress. The authors say maca "is capable of attenuating or even eliminating variations in homeostasis produced by stress," and it decreases or abolishes "stress-induced ulcers, elevated corticosterone levels, the reduction of glucose and the increase in the weight of adrenal glands produced by stress."

None of the studies reported any side effects. For men who are undergoing significant stress and feel their sex lives need a boost, maca may be the solution.

Laurie Steelsmith is a naturopathic physician and licensed acupuncturist in Honolulu, as well as author of the new book "Natural Choices for Women's Health," published by Random House. Reach her and read her past columns at www.DrSteelsmith.com. This column is for information only. Consult your health provider for medical advice.