Dementia isn’t an inevitable part of aging, even for those carrying multiple genetic risk factors for the brain-ravaging disease, a new study suggests.
Researchers who followed nearly 200,000 people found those at high genetic risk for dementia, but who didn’t smoke, who exercised regularly, drank alcohol in moderation and ate a Mediterranean-leaning diet lowered their dementia risk by a third.
The findings challenge the often fatalistic view of the memory-robbing illness, researchers said, and add to emerging theories that whatever is good for the heart is most probably good for the brain.
“A healthy lifestyle was protective, even for the people who had a bad luck of the draw with their genetic inheritance,” said Dr. John Haaga, of the U.S. National Institute on Aging, one of the study’s funders.
The study analyzed data from 196,383 people from the UK Biobank study, making it a considerably larger sample than anything done before.
All were aged 60 and older, and free of dementia, at the start of the study.
All were also genotyped, meaning their DNA was analyzed for genetic features linked to the risk of dementia, and then grouped into categories according to their risk: high, intermediate or low.
People were also given a score based on four recognized risk factors for dementia (smoking status, physical activity, diet and alcohol consumption).
“They told us a lot about themselves,” said lead author Dr. David Llewellyn, from the University of Exeter Medical School. For example: whether or not they smoked; how much fish they ate (the more the better); how much red meat they ate (“which is kind of more of a negative,” Llewellyn said); how many servings of fruits and vegetables they ate in a particular day; and how much they drank in a typical week.
People were then grouped into favourable, intermediate or unfavourable lifestyle categories.
Overall, people with a high genetic risk and an unhealthy lifestyle were nearly three times more likely to develop dementia compared to people with a low genetic risk and healthy habits.
But good habits lowered the risk regardless of a person’s genetic vulnerability. Among people with a high genetic risk, 1.13 per cent of those with a healthy lifestyle developed dementia after eight years of follow-up, versus 1.78 per cent of those with less wholesome habits.
According to Llewellyn, non-smokers, people who limited their alcohol consumption (moderate consumption was defined as no more than one standard drink a day for women, or two drinks per day for men), those who ate at least three servings of fruits and vegetables daily, and those who ate relatively little red meat scored highest on the lifestyle scale.
“Someone who maybe commutes to work — they cycle in for 20 minutes and cycle home again — that would tick the box in terms of being physically active,” he added.
It’s not just any one of these lifestyle changes, but the combination that appears to protect the mind.
The underlying mechanisms aren’t entirely clear, though there are several plausible hypotheses, Llewellyn said from Los Angeles, where he presented his group’s work at the Alzheimer’s Association International Conference. The human brain is a hungry organ. It requires a rich and constant supply of oxygen and glucose, and small disruptions to the blood supply to the brain make it vulnerable to dementia, he said.
The brain also has to clear away debris and protein abnormalities that, in large enough amounts, can be toxic and lead to the tangles and plaques linked to Alzheimer’s disease. “If your circulatory and lymphatic systems are working, they’ll do a better job of cleaning out the bad stuff,” Haaga said.
Most cases of dementia occur sporadically, in older people with multiple genetic risk factors.
“I think the fundamental message needs to be that, (most people) don’t know what your genetic risk of dementia is, and, even if you did, there is very little you can do about it,” Llewellyn said.
“But we need to be encouraged — if you live a healthy life you may be able to reduce your risk of dementia, whatever your genetic risk.”
More than 419,000 Canadians aged 65 and older are diagnosed with dementia, two-thirds of them women. It is the only major cause of death in Western countries without an effective treatment, despite billions spent trying to find one.
The study, published in this week’s issue of JAMA, the Journal of the American Medical Association, has several caveats. It doesn’t prove cause and effect, lifestyle factors were self-reported, people were followed up for a median of eight years only and some cases of dementia aren’t recorded in medical records or death registries.
However, while the number of people at risk of dementia, because of age, is growing rapidly as the population ages, a person’s individual odds of getting dementia have been going down, at least for the last two decades, Haaga said. There are a number of theories as to why, “but big ones are that we’re doing a better job of controlling cardiovascular risks, people have given up smoking and people are better educated at older ages than they used to be.”
Meaning, “There is some evidence that positive lifestyle has already been at work to help reduce the risk,” he said.
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Copyright Postmedia Network Inc., 2019
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