Until the early 2000s, we believed that dementia was the price we paid if we lost the genetic lottery, assuming we live long enough. Today, the scientific evidence suggests that circumstances we can control - lifestyle habits, medical conditions, and environmental factors - make up about 40% to 45% of the risk.
Kristine Yaffe , MD, a psychiatrist as well as a neurologist, has been at the vanguard of research into the association between cognitive decline, dementia risk and those factors we can control - what researchers call modifiable risk factors. These include smoking, high alcohol intake, poor sleep, limited exercise and social activity, low education and cognitive engagement, cardiovascular disease, head injury, vision and hearing loss, depression, and pollution.
We're approaching a watershed moment in the fight against dementia, according to Yaffe, professor of neurology, psychiatry, and epidemiology. These modifiable risks - together with existing and emerging medications that target Alzheimer's culprits, like amyloid, tau, and neuroinflammation - mean that we're closer to a multi-pronged treatment approach. This could transform an unstoppable disease into a more manageable one.
Which modifiable risks should we be paying most attention to?
We know from clinical-trial evidence that cardiovascular risk factors, like hypertension, high cholesterol, smoking, obesity, and physical inactivity, are very important. What happens to the heart directly impacts your brain's blood supply and cognitive health.
Our own SMARRT trial found that having older, higher-risk participants work with nurses and health coaches to reduce cardiovascular and other modifiable risks resulted in a boost in cognitive testing over two years, compared with those who did not undergo the intervention.
Do vaccines help reduce risk?
Vaccines are increasingly recognized as reducing the risk of cognitive decline. They can prevent severe viral and bacterial infections that promote systemic inflammation, cross the blood-brain barrier, and accelerate neurodegeneration. Recent studies also suggest that vaccines can stimulate immune cells that remove toxic proteins like amyloid and tau.
Routine vaccines, like flu and COVID, are associated with a lower risk of dementia, but the shingles vaccine appears to have a uniquely powerful effect. That's because it does more than just prevent infection; it suppresses the zoster virus, which has remained dormant in nerve cells since childhood chickenpox, a precursor to shingles. A 2025 study found that the shingles vaccine reduced cases of dementia by 20% over a seven-year period.
Why is poor sleep linked to dementia?
Research shows that poor sleep is linked to an increase in amyloid and tau, the hallmarks of Alzheimer's disease. The brain uses sleep to execute critical maintenance tasks, like flushing out toxic proteins, that cannot be performed when we're awake.
Our 2024 study showed that people with fragmented sleep, whose average age was 40, underwent cognitive testing years later and were up to 3 times as likely to score below those with normal sleep. Another study we did with midlife adults showed that poor sleep is linked to faster brain atrophy and Alzheimer's proteins in the blood.
What does exercise do to the brain that reduces our risk of dementia?
It triggers the release of BDNF, a protein that stimulates the birth of neurons in the hippocampus - the part of the brain responsible for learning and memory. Studies also show that it reverses brain shrinkage and optimizes brain health, decreases inflammation, and reduces vascular changes in the brain.
Exercise also improves blood flow to the brain and prevents the buildup of plaque, flushing out toxic proteins that can destroy brain cells.
Can diet play a role in preventing dementia?
Eating a lot of fat, sugar, and highly processed foods can increase the risk of cardiovascular disease, which can reduce blood flow to the brain - but it isn't a standalone factor. A Mediterranean diet based on olive oil, leafy vegetables, nuts, wholegrains, and fish has been associated with lower dementia risk. There have been a few studies that demonstrate this, but more research is needed.
What about dietary supplements?
Supplements should only be taken if there's a nutritional deficiency. There's some limited evidence to indicate multivitamins may be protective, for example, the COSMOS-Mind study of 2022 compared older adults taking multivitamins to those on placebo and found that it could slow cognitive aging. But longer-term studies are needed before clinical recommendations can be made.
Should I avoid artificial sweeteners in "sugar-free" and "diet" foods and beverages?
The science doesn't back that up - yet. Studies have been observational, meaning that one group that consumes artificial sweeteners is followed and compared with a second group that does not. These studies show correlation rather than causation. In this case, it could be that people with early metabolic issues switched to artificial sweeteners to manage their weight, so the underlying metabolic disorder caused dementia, not the diet soda and sugar-free snacks.
