Common prostate cancer treatment linked to Alzheimer's risk

Men undergoing hormone therapy as treatment for prostate cancer may be at a significantly greater risk of developing Alzheimer's disease, new research suggests.

"In this study, we did find that men who received hormone therapy had about an 88 percent increased risk of Alzheimer's disease," lead study author Dr. Kevin Nead of the University of Pennsylvania Perelman School of Medicine told CBS News.

The report, published in the Journal of Clinical Oncology, found that men who were on androgen deprivation therapy (ADT) for more than a year had the greatest risk of developing Alzheimer's.

Because testosterone can promote the growth of prostate tumors, doctors have used ADT to lower testosterone and other androgens in prostate cancer patients since the 1940s. Currently, about a half-million men receive ADT as a treatment for prostate cancer in the U.S.

"Testosterone has been shown to be important for the health of neurons," Nead said, "and neurons make up the brain and if we are not keeping those neurons healthy it could lead to an increased risk of Alzheimer's."

For the study, researchers from the Stanford University School of Medicine and the University of Pennsylvania Perelman School of Medicine analyzed the medical records of more than 16,000 patients with non-metastatic prostate cancer. Almost 2,400 had been treated with ADT.

"This is the kind of question that typically you would need a large clinical trial to answer," senior study author Nigam Shah, PhD, associate professor of biomedical informatics research at Stanford, said in a statement. But a formal clinical trial would be enormously expensive. "So instead, we're making secondary use of existing clinical data collected as part of routine medical care."

The researchers controlled for other potential risk factors, including age and heart disease.

But experts point out that the research only shows an association -- not a cause and effect relationship -- and that the overall risk of these patients developing Alzheimer's disease is still low.

"The benefits of continuing treatment far outweigh this theoretical risk based on this retrospective study," Dr. Matt Galsky, director of Genitourinary Medical Oncology at Mount Sinai Hospital, told CBS News.

Experts also say it's typically patients with advanced prostate cancer who are given ADT, so it's unclear whether the increased Alzheimer's risk is connected with the treatment or with the severity of the disease.