Up to two-thirds of Alzheimer's cases worldwide may stem from any of nine conditions that often result from lifestyle choices, a broad research review suggests.
Those include obesity (specifically, high body mass index, an indication of obesity, in midlife); carotid artery disease, in which plaque buildup narrows major neck arteries and slows blood supply to the brain; high blood pressure; depression; being frail; being poorly educated; having high levels of a naturally occurring amino acid known as homocysteine; and (specifically among those of Asian descent) being a smoker and/or having either type 2 diabetes.
The implication: Taking steps to minimize or eliminate such conditions might reduce the long-term risk for developing Alzheimer's, a brain disorder that affects memory and thinking. It is the most common form of dementia among seniors.
"The current evidence from our study showed that individuals would benefit from [addressing] the related potentially modifiable risk factors," said study lead author Dr. Jin-Tai Yu, an associate specialist in neurology at the University of California, San Francisco, and senior editor of the Journal of Alzheimer's Disease.
But Yu cautioned that "what is what is seen here is an association rather than a direct cause-and-effect relationship between any one factor and Alzheimer's risk." And that, he said, means it's impossible to determine exactly how much protection against Alzheimer's would be gained by the elimination of any one condition.
Yu and his colleagues discuss their findings in the Aug. 20 online issue of the Journal of Neurology, Neurosurgery & Psychiatry.
In all, investigators reviewed the findings of 323 studies completed between 1968 and 2014. Collectively, the studies involved more than 5,000 patients and looked at 93 conditions with the potential to affect Alzheimer's risk.
The team set out to determine which factors appeared to offer some protection against developing Alzheimer's.
On that score, the strongest evidence suggested that coffee, vitamins C and E, folate, NSAIDS (anti-inflammation drugs), statins (cholesterol-lowering drugs), blood pressure medications, and estrogen supplementation all appeared to reduce Alzheimer's risk.
Patients battling several serious health conditions also seemed to see their risk fall, including those with arthritis, heart disease, metabolic syndrome and/or cancer.
Those who were light or moderate drinkers of alcohol similarly saw their Alzheimer's risk dip, alongside current smokers (apart from those of Asian descent), those struggling with stress, and seniors with high body mass index.
By contrast, a complex statistical analysis enabled the research team to zero in on the nine factors that appeared to elevate Alzheimer's risk among 66 percent of those who ultimately get the disease.
But Dr. Anton Porsteinsson, a professor of psychiatry and director of the Alzheimer's Disease Care, Research and Education Program at the University of Rochester School of Medicine in Rochester, N.Y., suggested that to his mind, "there's not a lot of surprise here."
"It's an interesting paper," he said. "And certainly this review validates a number of individual studies that have previously shown an association between Alzheimer's and the factors they're identifying." But it doesn't improve understanding of the causes, he added.
The take-away, Porsteinsson said, is that a healthy lifestyle matters. Paying attention to blood pressure and cholesterol levels as well as exercise are all beneficial, and the other factors studied may make a difference, he added, but it doesn't mean there is a simple way to reduce Alzheimer's risk. Large clinical trials have looked at behavior modifications that might help, but those kind of simple interventions have failed.
"So reducing risk is probably not going to happen by just taking a pill or a food supplement or a single medication," he added. "That kind of a shortcut answer just doesn't have a lot of support."
