Cancer, chemo linked to vets' lower risk of Alzheimer's
BOSTON — Military veterans diagnosed with most forms of cancer were less likely to develop Alzheimer's disease, and those treated with chemotherapy got even more protection, finds a study released Monday at the Alzheimer's Association International Conference here.
The study of 3.5 million veterans found an inverse relationship between Alzheimer's and most types of cancer — not prostate and melanoma, which are largely detected through screening rather than symptoms. Aggressive screening of veterans might find cancers that would not otherwise have caused problems, said researcher Jane Driver, in explaining why those cancers might not share the same relationship with Alzheimer's.
More than 82,000 of the veterans developed Alzheimer's during the five years of the study, 24% of whom were previously diagnosed with cancer. When compared with projections for the general population, the risk of Alzheimer's was 51% lower than expected in liver cancer, 25% reduced in lung cancer and 13% lower in leukemia, according to the research. Other cancers' reduced risks seen in the study: pancreatic, 44%; esophageal, 33%; kidney, 22%; myeloma, 16%; lymphoma, 19%; head and neck, 15%.
There was no significant correlation between Alzheimer's and colorectal, bladder, stomach, genital, thyroid, sarcoma or brain cancer. Cancer patients who had chemotherapy lowered their Alzheimer's risk by 20%-45% for all cancers except prostate, the study showed. (Melanoma patients aren't typically treated with chemo.)
Other research also supports this inverse relationship, including an Italian study released late last week, that found that those diagnosed with Alzheimer's ran a 43% lower risk of developing cancer than those without the disease, and people with cancer had a 35% lower chance of developing Alzheimer's. That study, in the journal Neurology, did not look as closely at individual cancers or treatment differences, though it did find a weaker link with prostate cancer and melanoma.
Driver said chemotherapy may offer extra protection because it reduces inflammation and may prevent brain cells from trying to divide. In Alzheimer's, brain cells often try to divide when they shouldn't, leading to the cells' death, she said.
She said no one should take chemotherapy drugs, which are highly toxic, merely to reduce their risk of Alzheimer's, but the link suggests that it may be possible to develop medications to address both diseases. Certain chemotherapy drugs may turn out to be more protective of the brain than others, she added, so it may make sense to prescribe them more often.
Although it doesn't suggest any immediate treatments for Alzheimer's, the apparent connection with cancer is "one more puzzle piece" in helping researchers understand the memory loss and behavior changes from Alzheimer's, a fatal disease that affects an estimated 5.2 million Americans and is expected to strike nearly three times more over the next generation.
People with Alzheimer's suffer loss of memory, decreased thinking and language skills, and behavioral changes that can make caregiving challenging. Current treatments do not address underlying symptoms or stop progression of the fatal disease.
"We're starting to really understand what are the different pieces of the puzzle that make someone at increased or decreased risk," said Heather Snyder, director of medical and scientific operations for the Alzheimer's Association, the advocacy and research group that runs the international conference. "Understanding the pieces will help unlock additional targets and therapies and identify people at increased risk."
Another study released this morning showed that diabetics who take the drug Metformin seem to be better protected against Alzheimer's than those taking other diabetes medications, including Sulfonylurea. Nearly 26 million Americans have type 2 diabetes, which is largely associated with lifestyle factors. Roughly half of those with diabetes develop Alzheimer's as they age, so finding a drug that is also protective against Alzheimer's is immensely important, said researcher Rachel Whitmer, an investigator with the Kaiser Permanente Northern California Division of Research.
In her study of nearly 15,000 patients with type 2 diabetes, those who took Sulfonylurea had a 26% increased risk of developing Alzheimer's compared to those on Metformin. Not all patients can tolerate Metformin, but Whitmer said more research should certainly be done to see if that drug should be the first-line treatment for diabetes.
Among other studies discussed at the conference, which runs through Thursday:
-- Postponing retirement may protect against Alzheimer's and other forms of dementia, likely because it keeps people intellectually engaged for longer, a study of French shopkeepers and crafts workers suggests;
--Socioeconomic differences such as education and income – not lifestyle factors or health status – may explain why African-Americans are more likely to develop Alzheimer's than whites, according to a study led by Kristine Yaffe of the University of California, San Francisco.
-- An expert panel gathered by the University of British Columbia concluded that online tests for Alzheimer's are unreliable and unscientific as well as ethically questionable, because of likely conflicts of interest, lack of proper consent and privacy concerns.
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