WEDNESDAY, Dec. 23 (HealthDay News) -- Researchers have uncovered a bittersweet relationship between two major illnesses: cancer and Alzheimer's disease.
People who have had cancer are less likely to get Alzheimer's disease, just as having Alzheimer's disease reduces the risk for cancer, their study found.
"Alzheimer's was associated with a rather dramatic reduction in cancer risk," said Dr. Richard Lipton, an attending neurologist at Montefiore Medical Center and professor of neurology at Albert Einstein College of Medicine in New York City. "From my perspective, the strengths of the findings are very striking and somewhat unexpected."
There was no link between Alzheimer's and vascular dementia, however, suggesting that the association has to do with neurodegenerative factors. Vascular dementia is attributed to damage to the brain's blood supply.
"Parkinson's and Alzheimer's are both neurodegenerative diseases, where specific populations of cells die without clear reason," Lipton said. "In cancer, specific populations of cells begin dividing wildly and out of control so, very broadly, it makes sense that a condition associated with selective cell death may be associated with a condition associated with proliferation. The biological factors that predispose one to neurodegenerative disease may protect against wild division."
A number of previous studies had hinted at a similar relationship but were subject to the usual limitations of early research.
For example, said Catherine M. Roe, lead author of the new study, published Dec. 23 in Neurology, earlier research could not pinpoint whether cancer patients died before they had a chance to be diagnosed with Alzheimer's. Roe is an instructor in neurology at Washington University in St. Louis School of Medicine.
As the accompanying editorial pointed out, the main reason older people with advanced brain tumors don't get Alzheimer's is that they just don't live long enough.
In Roe's study, 3,020 people 65 and older enrolled in a cognition sub-study of the large Cardiovascular Health Study were followed for an average of five years for dementia and eight years for cancer.
Among white participants, those who had Alzheimer's at the start of the study were 69 percent less likely to be hospitalized for cancer. Having cancer meant a 43 percent reduced risk for Alzheimer's.
Among minority participants, the researchers found an opposite trend, but it was not statistically significant, they noted.
There appeared to be no link either way between vascular dementia and cancer.
Next, Roe said, the research team would like to see whether there's an association between Alzheimer's disease and specific types of cancer.
The Alzheimer's Association has more on Alzheimer's disease.
SOURCES: Catherine M. Roe, Ph.D., instructor, neurology, Washington University in St. Louis School of Medicine, St. Louis; Richard Lipton, M.D., attending neurologist, Montefiore Medical Center, and professor, neurology and epidemiology, Albert Einstein College of Medicine, New York City; Dec. 23, 2009, Neurology, online