[A picture is emerging of a healthy lifestyle which is key to the
condition’s prevention – exercise, being sociable, and looking
after your ears]
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THE SCIENCE BEHIND DEMENTIA AND THE FOUR THINGS YOU SHOULD DO TO
PREVENT IT  
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Ian Sample
March 11, 2023
Guardian
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_ A picture is emerging of a healthy lifestyle which is key to the
condition’s prevention – exercise, being sociable, and looking
after your ears _

Running, by kevin dooley (CC BY 2.0)

 

The idea was simple. Recruit hundreds of people in their 80s and 90s,
equip them with fitness trackers, and monitor their physical activity.
Then, when the participants died, collect their brains and examine the
tissue. Is there evidence, lurking in the tissue, that exercise
benefits the brain?

The results, from a 2022 collaboration between the University of
California in San Francisco and the University of British
Columbia, were striking
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Physical exercise, late in life, seemed to protect the ageing
connections between brain cells – the synapses where memories are
made. The work, if backed up by further studies, could see exercise,
and potentially drugs that mimic biochemical aspects of activity –
prescribed to help slow the onset of dementia
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We know there is a 30%-80% reduced risk of dementia in people who
exercise

“We know there is a 30%-80% reduced risk of dementia in people who
exercise,” says Kaitlin Casaletto, the lead author on the study and
an assistant professor in neurology at UCSF. “My question was,
wouldn’t it be cool if we could figure out exactly how this is
happening? If we could identify some of the mechanisms of exercise for
brain health? These are potential therapeutic targets we can
bottle.”

A small mountain of work has linked physical exercise to better brain
health and lower risk of dementia in older age. One recent study
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nearly 80,000 people in the UK found that the risk of dementia was
halved in people who reached the goal of 10,000 steps a day. But much
is still unclear. Part of the observed benefit could be down to people
with healthier brains simply exercising more. While there are definite
benefits to be had from exercise – greater blood flow to the brain,
better cardiovascular health, lower blood pressure, less obesity and
diabetes – there is still plenty to nail down.

Dementia is the number one killer in the UK, with the disorder
affecting about 900,000 people. Most cases, about two-thirds, are
driven by Alzheimer’s
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far from the only cause. Other forms, namely vascular dementia,
dementia with Lewy bodies
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and frontotemporal
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arise from other processes. Whatever the cause, the steady destruction
of brain cells erodes memory, thinking, movement and personality. In
old age, dementia can be several of these conditions at once.

Some of the highest rates of dementia are found in developed
countries with older populations
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In Germany, Italy and Japan, more than 20 in every 1,000 people have
dementia compared with fewer than nine per 1,000 in proportionally
younger countries including Mexico, Turkey and South Africa. The UK
sits in the middle. Indigenous groups
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have some of the lowest rates. In one recent study
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researchers confirmed only six cases among 604 Bolivian Tsimane and
Moseten people aged 60 and over, suggesting that lifelong physical
activity and healthier preindustrial diets substantially reduce the
risk. Over the next three decades, global dementia is due to rise
substantially, particularly in north Africa, the Middle East and
eastern sub-Saharan Africa, where population growth and ageing will be
among the driving forces.

But dementia is not inevitable, nor is it the reward for dodging other
fatal conditions. Take all of the risk factors that we as individuals,
or nations through their policies, might improve, and potentially 40%
of cases could be prevented or delayed. We would not eradicate
dementia, and many people who did everything to keep their brains
healthy would still succumb to the disease. We could, however,
dramatically reduce the risk, meaning more years of sound thinking,
intact memories and independent living. “That figure, 40%, is an
enormous percentage,” says James Rowe, professor of cognitive
neurology at the University of Cambridge. “If we had a drug that
could cut dementia by 40%, it would be a phenomenal success.”

Our brains change even with healthy ageing. People vary tremendously,
but vocabulary often improves past retirement age, while processing
speed, the ease of learning new information, cognitive flexibility,
and working memory – for example, how many digits of a phone number
you can remember – weaken. Learning more slowly in older age is
often framed as a negative, but it has its advantages. Young people
know so little that learning everything fast makes sense. But older
people weigh new information against a lifetime’s learning. Does it
fit with what I know to be true? Is it reliable? Does it deserve to be
learned? “When you are born, you are fast but know little. When you
are old, you are slower but knowledgeable. Which is better? It depends
on the situation,” says Rowe.

Dementia is very different to healthy ageing. It is what happens when
brain cells are destroyed by disease. A healthy older person can
expect a gradual decline in memory and thinking skills, but people
with dementia can develop profound problems with memory, judgment,
language, concentration and personality. The sharp decline in
performance is mirrored by a pronounced shrinkage of the brain.

Last year, researchers at the universities of Cambridge and
Pennsylvania stitched together 125,000 brain scans
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the human brain changes from a 15-week-old foetus to a 100-year-old
adult. The work was a tour de force. Ultimately, it should allow
doctors to assess how a person’s brain is ageing over their
lifetime, much as paediatric growth charts allow them to check whether
children are developing normally. For example, a person’s brain
might be in the 50th centile at age 45, but if it falls significantly
on subsequent scans there may be a problem. The researchers already
see stark shifts in scans from people diagnosed with Alzheimer’s.
“We see those individuals crashing through the centiles,” says
Richard Bethlehem, an assistant professor in neuroinformatics at
Cambridge.

A lot of the seeds of poor brain health are sown in childhood and then
built on through early adult life and middle age

Because dementia is seen as a problem of old age, this might seem like
the time to act. But ageing is a lifelong process: the better the
brain ages, the better it can stave off or withstand dementia. “A
lot of the seeds of poor brain health, including dementia, are sown
well and truly in childhood and then built on through early adult
life and middle age,” says Rowe. “The state of our brain health in
late life, when we are conventionally worried about dementia, depends
on a whole lifespan of lifestyle and activities.”

In 2020, 28 world leading experts published a major report called
the Lancet Commission on dementia
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identifies a dozen “potentially modifiable” factors that affect
our risk of developing dementia. Which matters most depends on age. In
youth, a good education makes an enormous difference, and benefits
brain health for the rest of life. In midlife, not boozing too heavily
and controlling blood pressure all come into play. In later life, not
smoking, exercising regularly and keeping socially engaged stand out.

How these help to prevent dementia is not always straightforward. A
good education doesn’t happen in a vacuum. It can reflect a
child’s circumstances: their home environment, household income and
expectations all play a part in sculpting the brain. Armed with a good
education, people are better equipped to look after themselves. But
education seems to act directly on the brain too, creating what
researchers call cognitive reserve and resilience. Build up brain
capacity early in life and that reserve becomes a shield against
future damage. Likewise, education boosts resilience, the brain’s
ability to compensate when diseases like Alzheimer’s arise. The
impact can be striking. “For people with a very high education, when
you look at the brain postmortem, they can have a lot of
neuropathology without having had any symptoms,” says Gill
Livingston, professor of psychiatry of older people at University
College London and lead author of the Lancet report. In short, the
disease is there, but the brain can withstand it, at least to the
point that obvious symptoms never manifest.

According to the Lancet Commission, poor education accounts for 7% of
dementia worldwide. But the benefits of stretching one’s brain
don’t end in youth. People who do cognitively challenging jobs have
a lower risk of dementia
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too, regardless of their education. As the Lancet report puts it:
“The use it or lose it hypothesis suggests that mental activity, in
general, might improve cognitive function.” The impact of other
brain-stretching activities is far from clear, however. Despite a
flurry of brain training programmes being developed to boost cognitive
skills, there is no good evidence
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people improve at anything apart from the particular task they
practise.

One message that runs through all the research on dementia prevention
is that a healthy lifestyle helps. Diet is important: you cannot grow
a good brain without good nutrition, and a healthy diet helps to
maintain it. A recent meta-analysis of studies
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people, found that strict adherence to the Mediterranean diet
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associated with a 21% lower risk of cognitive disorders and a 40%
lower risk of Alzheimer’s. Whether specific nutrients and compounds
are directly beneficial to the brain is the focus of intensive
research, but healthy diets
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encouraged regardless, because they reduce risks caused by other
disorders, such as high blood pressure, poor vascular health, obesity
and diabetes.

Which single intervention could reduce dementia risk the most?
Preventing hearing loss

Which single intervention could reduce dementia risk the most? The
answer is one that even some researchers find surprising:
preventing hearing loss
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impairment is believed to account for about 8% of dementia. Hearing
loss means less stimulation for the brain, but also more social
isolation for the individual. The brain appears to shrink more
rapidly, or at least the temporal lobes, which focus on sound
processing, emotions and memories. What’s striking is that the link
between hearing loss and dementia is all but absent if people wear
hearing aids. Livingston believes this is a huge opportunity. While
people with poor eyesight tend to have it corrected, a large
proportion of those who cannot hear well either think other people
mumble, or are reluctant to wear a hearing aid. Correcting hearing
loss as well as we correct poor sight could be a gamechanger, if
enacted globally. “I think wearing a hearing aid is still
stigmatised,” Livingston says, but she wonders, with more and more
people now wearing earbuds, whether that barrier will soon fall too.

The picture emerging from decades of research is that the best
protection against dementia comes from building a good brain, keeping
it healthy and active, and avoiding too much damage. The latter can
happen in seconds or years. Brain injuries
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from traffic accidents, military service, falls, or impacts during
sports such as boxing, rugby and horse riding, all increase the risk
of dementia. So does the sustained damage that comes with smoking, air
pollution and excessive alcohol intake – over 21 units a week. Brain
injuries are thought to account for about 3% of dementia, with heavy
drinking and smoking making up 1% and 5% respectively. Air pollution
accounts for around 1% of dementia.

Seven healthy habits may help cut dementia risk, study says
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As might be expected, some experts in the field already take steps to
reduce their risk. Because it is unclear which exercises are most
protective, Dr Casaletto does weekly yoga
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includes high-intensity sprints in her routine. She eats healthily,
maximising the vegetables, whole grains, olive oil, fish and legumes
of the Mediterranean diet. Then there is the cognitive component. She
tries to stay socially and mentally curious – pushing herself at
work, broadening her collaborations, and hanging out with people she
wouldn’t normally socialise with. “I think novelty is really
important,” she says. “If we are doing the same thing over and
over, we are not going to be pushing our brains into forming new
connections.”

As part of her own risk-reducing lifestyle, Prof Livingston lifts
weights and tries to reach 10,000 steps a day, even though she
acknowledges it is “not a magic number”. She reads and writes. And
she is wary of the impact of giving up work. “I can see that not
being retired keeps you so much more active in lots of ways,” she
says. “It might make me less likely to retire. Though I do hope that
if I get to the stage when I ought to because I can’t function, that
my colleagues will tactfully let me know.”

Four changes to make now

Dementia research, like all research, comes with caveats. Most studies
cannot prove that doing X instead of Y helps fend off dementia. More
commonly, scientists find associations, such as older people who
exercise develop less dementia. But there is always the risk of
reverse causation. What if people prone to dementia simply exercise
less? Whether, and to what extent, exercise protects people’s brains
can take some unpicking. The bottom line on whether this or that
action keeps dementia at bay is rarely clear cut. Often the picture
emerges with time, as evidence builds from different directions. But
these are some things that you can do to help reduce the risk.

Keeping physically active matters. By combining the results
from multiple studies
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scientists find have found time
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Alzheimer’s are less common in people who exercise. Sustained
exercise in midlife, and possibly later life, appears to protect
against dementia. A mix of aerobic exercise and strength training
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effective. For aerobic exercise, breaking into a sweat at least once a
week or doing more than 150 minutes of moderate to vigorous exercise
each week have both been shown to be protective. How exercise helps is
a focus of ongoing research, but at the least, it can reduce the risk
of obesity and diabetes while boosting cardiovascular fitness, all of
which lower dementia risk. Other gains can be had from quitting
smoking and not drinking too much alcohol.

Less intuitive than mental and physical fitness is the impact of
hearing loss. Poor hearing in middle age is thought to be one of the
most significant drivers of dementia that people can act on. The
mechanisms are still being teased out, but brain scans have linked
poor hearing to faster brain shrinkage, itself a driver of dementia.
Hearing loss also drives up social isolation, which compounds the
problem, as people withdraw from social gatherings and the
conversations they entail. But there is good news emerging: the marked
declines seen in people with hearing impairments are not as dramatic
in people who wear hearing aids
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suggesting that correcting the problem can help keep dementia at bay.A
good chunk of people’s resilience to dementia comes from early life
education. But even after school or university, keeping the brain
mentally engaged matters. It is important for the brain to be making
new connections. This means challenging yourself mentally, setting
your brain to work on varied, unfamiliar and cognitively complex
issues. A mentally challenging job may help
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learning, engaging hobbies and keeping socially active
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especially if you mix with people you wouldn’t normally hang out
with. Being more sociable in your 50s and 60s
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linked to better cognitive performance and a lower risk of dementia
later in life, perhaps because it gets people using their memory and
language skills. Keeping the brain active builds “cognitive
reserve”, researchers say, meaning the brain is better able to cope
as the pathologies that drive dementia take hold.

PRIORITISE DENTAL HYGIENE

One of the more speculative ideas on how to reduce dementia risk comes
from research into bugs in the mouth. A recent study
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people with gum disease and mouth infections were more likely to
develop Alzheimer’s
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the most common cause of dementia. Work is now under way to check
whether bacteria such as Porphyromonas gingivalis help drive the
condition, or simply proliferate in people in the early stages of
dementia. If bacteria raise the risk, there will be even more reason
to properly brush and floss twice a day.

_Ian Sample is science editor of the Guardian. Before joining the
newspaper in 2003, he was a journalist at New Scientist and worked at
the Institute of Physics as a journal editor. He has a PhD in
biomedical materials from Queen Mary's, University of London. Ian also
presents the Science Weekly podcast
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