Karen Weintraub, Special for USA TODAY
The study of 3.5 million veterans found an inverse relationship between Alzheimer's and all types of cancer except prostate and melanoma - both of 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.Military veterans diagnosed with most forms of cancer were less likely to develop Alzheimer's disease, and those who were treated with chemotherapy received even more protection, according to a study released this morning at the Alzheimer's Association International Conference in Boston.
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 did not look as closely at individual cancers -- though it did find a weaker link with prostate cancer and melanoma -- or at treatment differences.
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 their death, she said.
She said no one should take chemotherapy drugs, which are highly toxic, 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.
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.
Other research discussed at the conference this morning suggests that postponing retirement may protect against Alzheimer's and other forms of dementia, likely because it keeps people intellectually engaged for longer; and that socioeconomic differences like education and income - not lifestyle factors or health status - may explain why African-Americans are more likely than whites to develop Alzheimer's.