Published on: December 17, 2016
by Joshua C. Kendall for UnDark:
Despite a growing conviction among researchers that lifestyle choices matter, Americans still view Alzheimer’s as a predominantly inherited disease.
Over the course of her 25-year career as a neuropathologist, Ann McKee, associate director of Boston University Alzheimer’s Disease Center, has dissected thousands of brains — but two in particular stick with her. It was about a decade ago, and the brains belonged to identical twins who both died in their 70s. While one twin developed Alzheimer’s in his mid-60s, the other never showed any signs of cognitive impairment.
“Almost everything about them was the same,” McKee says, “Genes, education and even profession — both were chemical engineers.” But one major difference stood out. The twin who developed Alzheimer’s worked in a Union Carbide plant for three years where he was regularly exposed to large amounts of DDT.
In 2009, McKee, along with a team of Arizona researchers, published a paper, “Epigenetic Differences in Cortical Neurons from a Pair of Monozygotic Twins Discordant for Alzheimer’s Disease” in the journal PlosOne, in which she offered a new way of thinking about the genetic mechanisms responsible for Alzheimer’s disease.
Instead of looking just for inborn genetic differences, McKee and her colleagues suggested, researchers also need to study the potential influence of life events. In her article, she reported that the cortical neurons of the twin with Alzheimer’s exhibited reduced levels of DNA methylation, a mechanism which controls gene expression, compared to those of the other twin. This is a finding that has been seen in other cases of the disease, and one that McKee suspects is attributable to the afflicted twin’s work in the Union Carbide plant. Subsequent research has lent further support to a link between DDT and the onset of Alzheimer’s. In a study funded by the National Institute of Environmental Health Sciences and published in JAMA Neurology in 2014, scientists found that levels of DDE — a breakdown product of DDT — were 3.8 times higher in the blood samples of patients with Alzheimer’s than in those of comparable subjects without the disease. And DDT isn’t the only risk factor.
Studies have also found a link between brain injuries early in life (and sometimes not so early), and the onset of Alzheimer’s years later — including among Gulf War veterans who suffered traumatic brain injuries. Other studies have found troubling signs of cognitive impairment — the first phase of Alzheimer’s — among 9/11 first responders, suggesting that there might be a common environmental trigger. The lead author of that study, which found that 13 percent of 800 first-responders suffered from some form of cognitive impairment, while 1.2 percent had possible dementia, called the findings “staggering,” given that the average age of the respondents was only 53.
Similarly, scientists have also been studying associations between Alzheimer’s and a variety of other life events and lifestyle choices. Alzheimer’s Disease International, a federation of Alzheimer’s associations from around the world, summarized many of the key findings of this body of research in its 2014 report, “Dementia and Risk Reduction: An Analysis of Protective and Modifiable Factors.” The report identified four categories of risk factors: developmental (say, a lack of formal education); psychological (depression, for example, or a sleep disorder); lifestyle (smoking, diet, and so forth); and cardiovascular (hypertension or diabetes, among others) — all of which have been repeatedly linked to Alzheimer’s.
And yet for all of this, the general public still holds a variety of outdated ideas about the nature of Alzheimer’s — the most common being that this neurodegenerative disease stems solely from faulty genes. Indeed, a review article on the public’s understanding of Alzheimer’s disease published last year in the journal Alzheimer’s Disease and Associated Disorders noted that “while the public’s knowledge of genetic risk factors seems to be fair to good, knowledge of modifiable risk factors for dementia is poor.”
To back up this conclusion, the authors cited one study in which only about a quarter of respondents were aware that hypertension and high cholesterol increase an individual’s risk of developing dementia, and another study in which only about a third of respondents identified smoking as a risk factor.
The research on modifiable risk factors, of course, is still relatively new, and most of the studies conducted over the last two decades are observational, providing only links and associations. But the vast majority of clinicians who treat Alzheimer’s patients are now convinced that common-sense lifestyle adjustments can often help either ward off the disease or slow its progression. Researchers may not know precisely what exactly triggers Alzheimer’s in some people and not in others, but evidence suggests that what we eat, how we live, the way we think, and other factors are likely to play a role. As Robert Roca, vice president of medical affairs at Baltimore’s Sheppard Pratt Health System puts it, “The good news is that if you take simple steps that are beneficial for your overall health, you can reduce your risk.”
And just as public health campaigns extolling the benefits of diet, exercise, and quitting smoking have helped to raise awareness that reducing the risk of heart disease is at least partly within our control, so too, experts say, should more be done to increase public understanding of the controllable risk factors associated with Alzheimer’s. Indeed, some of the same measures that protect against cardiovascular disease — regular exercise, a diet heavy in fruits and vegetables — also protect against Alzheimer’s. “What is good for heart,” Roca says, “is also good for the brain.”
Those sorts of preventive insights are as crucial to combatting the disease as any hunt for a cure, suggests McKee, who has also done extensive research on neurodegenerative diseases in the brains of athletes like boxers and professional football players. Just as these individuals might have prevented their own disease by avoiding high-risk activities, McKee thinks much more needs to be done to educate the public on the types of activities that can increase risk for Alzheimer’s — as well as those activities that can decrease risk.
“We don’t have to step into the boxing ring, and we can also control vascular function, which often plays a huge role in Alzheimer’s disease,” McKee says.
“The brain and the heart actually have a lot in common,” she adds. “Both organs are responsive to what is going on in the rest of the body — and to our life experiences.”
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