People who have Alzheimer's disease may be less likely to develop cancer, and people who have cancer may be less likely to develop Alzheimer's disease, according to a new study published in the December 23, 2009, online issue of Neurology, the medical journal of the American Academy of Neurology.

"Discovering the links between these two conditions may help us better understand both diseases and open up avenues for possible treatments," said study author Catherine M. Roe, Ph.D., of Washington University School of Medicine in St. Louis, MO, and a member of the American Academy of Neurology.

For the study, researchers looked at a group of 3,020 people age 65 and older who were enrolled in the Cardiovascular Health Study and followed them for an average of five years to see whether they developed dementia and an average of eight years to see whether they developed cancer. At the start of the study, 164 people (5.4 percent) already had Alzheimer's disease and 522 people (17.3 percent) already had a cancer diagnosis.

During the study, 478 people developed dementia and 376 people developed invasive cancer. For people who had Alzheimer's disease at the start of the study, the risk of future cancer hospitalization was reduced by 69 percent compared to those who did not have Alzheimer's disease when the study started. For Caucasian people who had cancer when the study started, their risk of developing Alzheimer's disease was reduced by 43 percent compared to people who did not have cancer at the start of the study, although that finding was not evident in minority groups.

The study was supported by the National Institutes of Health, the National Heart, Lung, and Blood Institute, the National Institute of Neurological Disorders and Stroke, the National Institute on Aging, the National Center for Research Resources, and the Washington University Alzheimer's Disease Research Center.