After menopause women are advised to start taking estrogen to replace the dwindling supply of the hormone in their bodies. In addition to relieving menopausal symptoms and preventing osteoporosis, some studies suggest estrogen may improve older women's memory.

But now researchers are questioning whether supplements of male hormone may do the same for older men experiencing what some doctors refer to as "male menopause."

Like estrogen, testosterone declines with age, though not as rapidly. But according to Monique Cherrier, PhD, the loss of testosterone can cause subtle changes that make memory less sharp and may even increase the risk of Alzheimer's disease.

Cherrier and colleagues from the University of Washington Medical School in Seattle gave 25 older men, who had low levels of testosterone but were otherwise healthy, injections of testosterone or a placebo weekly for six weeks. Tests of different types of memory were conducted before the study began, at the midway point and again at the end.

Compared to men who only received placebo, those who got testosterone had significant improvements in a test of spatial memory -- which is memory for information such as the geographical layout of your hometown or the inside of a friend's house. They also had improvements in verbal memory, which is memory for words and verbal items, like the ability to recall a short story.

The study appears in the July issue of Neurology.

"This is a very controversial area and there are not that many studies," says Wayne Hellstrom, MD, but, he adds, there is early evidence to indicate that men who have low testosterone show memory improvement when testosterone is replaced.

Hellstrom, a professor of urology at Tulane University Health Sciences Center in New Orleans, says testosterone replacement may have many benefits, but a man must have testosterone levels that are significantly below normal for it to work.

"If that's the case, he can definitely benefit," he says. "Probably the most important area where it can help is with prevention of osteoporosis."

Hellstrom says there is also evidence that testosterone helps maintain strength and muscle tone and may improve libido and mood as well.

Abraham Morgentaler, MD, who frequently prescribes testosterone replacement, agrees that testosterone has much to offer men as they age.

"Certainly improvement of memory is one of those things," he tells WebMD. "In the past we focused almost exclusively on the sexual benefits and ... it's only recently that we are looking at this again from the nonsexual aspects of what testosterone can do."

But a major concern is the potential for testosterone to increase the risk of prostate cancer.

"It won't cause prostate cancer, but if a person has a [hidden] prostate cancer it can encourage it to keep on growing," says Hellstrom. Also, if a person has an enlarged prostate, testosterone can make it grow and impair urination.

"If someone is on testosterone for any reason and they are older than 50, they need to be monitored ... probably on a six-month basis," says Morgentaler, an associate professor of surgery at Harvard Medical School. He suggests the men have both blood tests and a physical examination.