(HealthDay News) – Being a cancer survivor and having been treated with chemotherapy seem to confer a protective effect against Alzheimer’s disease (AD), according to a study presented at the annual Alzheimer’s Association International Conference, held from July 13–18 in Boston.

Laura Frain, MD, from the VA Boston Healthcare System, and colleagues analyzed the medical records of 3,499,378 veterans aged ≥65 years who were seen for treatment between 1996 and 2011. Participants were free of dementia at baseline. The relationship between a history of 19 different cancers, cancer treatment, and subsequent AD was assessed.

The researchers found that, over a median of 5.65 years of follow-up, 82,028 veterans were diagnosed with AD. Of those veterans with AD, 24% had a history of cancer. Most types of cancer were associated with reduced AD risk, with the risk reduction ranging from 9–51%. Survivors of liver cancer (51% lower risk), cancer of the pancreas (44%), cancer of the esophagus (33%), myeloma (26%), lung cancer (25%), and leukemia (23%) had the greatest risk reductions. Regardless of cancer type, AD risk was reduced by 17% to 23% in those who received chemotherapy and/or radiation. The reduced risk of AD was not associated with melanoma, prostate cancer, and colorectal cancer. Cancer history did not reduce risk for any other typical age-related health outcome, with cancer actually associated with an increased risk of stroke, osteoarthritis, cataracts, macular degeneration, and non-Alzheimer’s dementia.

“We found that the majority of cancers have an inverse relationship with AD even after adjustment for treatment,” Frain and colleagues conclude. “Reception of chemotherapy was associated with a reduced risk for subsequent AD in nearly all cancers.”

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