The risks of dementia, cancer and vascular disease increase with age, but the connection between the conditions is not fully understood. Now, Mayo Clinic researchers report an intriguing finding: Having a history of cancer or coronary artery disease may actually reduce the risk of dementia. Their study results are published in the Journal of Alzheimer's Disease.
People 85 and older are the fastest growing segment in the U.S., with the percentage of those in that age bracket expected to more than double to 4.8% by 2050, according to the U.S. Census Bureau. As a result, Alzheimer's disease, the fifth-leading cause of death among Americans 65 and older, remains a top disease of concern as the most common form of dementia.
The researchers set out to determine how a history of cancer or vascular disease in individuals may influence a future risk of dementia. They analyzed data between 1998 to 2020 from a unique group of Mayo Clinic study participants who died at age 95 or older, had undergone an autopsy and had donated their brains to the Mayo Clinic Brain Bank for research.
Researchers evaluated medical records for a documented history of cancer or vascular disease, such as coronary artery disease and diabetes. Statistical analysis, neuropathology reports and modeling were used to conduct the study.
The study found that a past history of cancer reduced the risk of dementia and was associated with a lower amount of Alzheimer's disease brain changes, such as buildup of the toxic tau protein, a hallmark of the disease. "It may be the result of underlying molecular changes that oppose each other," says Melissa Murray, Ph.D., a neuroscientist and senior author of the study. "Cancer wants to proliferate, or expand and grow, whereas molecular changes associated with Alzheimer’s disease wants to kill cells. It could be a tug of war." Dr. Murray leads the Translational Neuropathology Laboratory at Mayo Clinic in Florida.
Researchers say it is possible that common genes and mechanisms normally involved in cell growth and maintenance may be regulated in opposite directions. They speculate that increased pro-growth mechanisms may increase cancer risk, while increased cell death mechanisms may increase dementia risk. Although the topic was not studied in this paper, they note that treatments for cancer, such as chemotherapy, also may affect brain cells and prevent the formation and spread of proteins associated with age-related neurodegenerative diseases. They say a better understanding of what is happening inside the brains of patients before, during and after cancer treatment would be beneficial in identifying factors that promote or prevent dementia.
The research team also studied vascular risk factors, such as smoking, hypertension and diabetes, in calculating the odds of developing dementia. While all these conditions increased risk, they found that diabetes was the strongest contributing risk factor. Surprisingly, the researchers found that a history of coronary artery disease also was found to decrease the risk of dementia. They hypothesize that this could be associated with the benefits of treatment over many years for known disease. Medications used to treat coronary artery disease are designed to reduce dangerous plaques in the coronary arteries and promote the health of blood vessels in the brain.
The researchers recognize that controlling vascular risk factors is a promising strategy for lowering the risk of dementia and say their study results support living a healthy lifestyle overall.
"I think it really does point to a need to emphasize the importance of avoiding diabetes and the potential importance of being treated for coronary artery disease," Dr. Murray says.
This research was funded in part by the Alzheimer's Association, National Institute on Aging, National Institute of Neurological Disorders and Stroke, the Florida Department of Health, and the Ed and Ethel Moore Alzheimer’s Disease Research Program. For a full list of funding, authors and disclosures, see the published paper.