Diagnoses of Alzheimer’s
or cancer are never good news, but they may come with a small silver lining.
Scientists have found that having Alzheimer’s reduces the
risk for cancer, just as a diagnosis of cancer brings a reduced likelihood of developing
the brain disorder.
In a study
published online in Neurology
Dec. 23, scientists report on results from more than 3,000 people, all at least
65 years old, enrolled in an extended survey of cardiovascular health. Those
who entered the survey with Alzheimer’s had a 69 percent reduced chance to be
hospitalized due to cancer. Those who had cancer at the outset were 43 percent
less likely to develop Alzheimer’s, at least in Caucasians. (In other ethnic
groups, the opposite seemed to hold true, although sample sizes were too small
to provide reliable data in these populations.)
But no association was found between cancer and vascular
dementia, the second most common form of dementia after
Alzheimer’s. Unlike Alzheimer’s, which is characterized by abnormal proteins
that lead to brain cell death, vascular dementia stems from clogged blood
vessels that starve neurons of oxygen.
The reasons for these trends are not clear, since the study
looked at overall health trends and was not designed to investigate causes. But
the authors speculate that the findings imply that cancer and Alzheimer’s share
some common molecular basis that vascular dementia does not.
Previous studies have also found links between cancer risks
and neurological disorders. Parkinson’s
patients, in particular, have a
reduced risk for many cancers; one possible cause, scientists think, is
that Parkinson’s causes increased apoptosis—or programmed cell
“suicide”—throughout the body, stifling many cancers before they have a chance
to establish themselves.