A human brain showing fronto-temporal lobe degeneration, often associated with dementia

A human brain showing fronto-temporal lobe degeneration, often associated with dementia

Dementia is a significant health burden of increasing significance as our population ages. Worldwide the prevalence of dementia is 5-7% in people 60 years and older, with risk doubling every 5 years after age 60. About 5.4 million Americans are living with dementia.

Dementia is a general category referring to a chronic decline in overall cognitive function. The most common cause of dementia is Alzheimer’s disease, accounting for about half of cases. There is also a category of mild cognitive impairment (or cognitive impairment not dementia) that is milder and does not meet the diagnostic criteria for full dementia.

Declining prevalence

There is some good news, however. A recent study published in JAMA finds that in the US the prevalence of dementia in those 65 and older declined between 2000 and 2012, from 11.6 to 8.8%. This is both statistically significant and clinically significant.

This also mirrors evidence from other countries also showing a decline in dementia prevalence over the last 20 years, including the UK, Denmark, and Sweden.

The big question, of course, is what is causing this decline? If we can determine the major factors then perhaps we could use that knowledge to further decrease dementia risk.

The JAMA study was not designed to answer that question, but it did collect basic demographic information that provides at least some clues. They found a correlation between years of education and decreased risk of dementia, enough to explain part but not all of the decline. Overall the average years of education in the study cohort increased from 11.8 to 12.7 from 2000 to 2012.

This is not a new finding. Overall the evidence strongly suggests that anything you do to make your brain work harder has a protective effect against developing dementia. For example, one study found those who were bilingual presented with dementia on average three years older than those who are monolingual.

A 2016 systematic review looking at mental leisure activity and cognitive decline found an overall significant protective effect.

However, brain training games specifically have not fared well. Despite controversial claims by companies selling brain training, the evidence has not found a significant protective effect. A 2014 consensus statement by researchers concluded:

We object to the claim that brain games offer consumers a scientifically grounded avenue to reduce or reverse cognitive decline when there is no compelling scientific evidence to date that they do. The promise of a magic bullet detracts from the best evidence to date, which is that cognitive health in old age reflects the long-term effects of healthy, engaged lifestyles. In the judgment of the signatories below, exaggerated and misleading claims exploit the anxieties of older adults about impending cognitive decline. We encourage continued careful research and validation in this field.

A study published this year (the ACTIVE trial) has been getting a lot of press because it reports a protective effect for a specific type of video game, one that trains speed of processing (but not ones that train memory). They found:

At mean age of 82 years, about 60% of trained participants compared to 50% of controls (p<.05) were at or above their baseline level of self-reported IADL function at 10 years. The reasoning and speed-of-processing interventions maintained their effects on their targeted cognitive abilities at 10 years (reasoning: effect size, 0.23 [99% CI, 0.09-0.38]; speed-of-processing: effect size, 0.66 [99% CI, 0.43-0.88]). Memory training effects were no longer maintained for memory performance. Booster training produced additional and durable improvement for the reasoning intervention for reasoning performance (effect size, 0.21 [99% CI, 0.01-0.41]) and the speed-of-processing intervention for speed-of-processing performance (effect size, 0.62 [99% CI, 0.31-0.93]).

While interesting, this is one study, subject to all the sources of bias and p-hacking that we frequently discuss on SBM. It is not enough to reverse the consensus of prior research, but it does indicate that more research is needed.

There is also good evidence that physical activity is associated with improved cognitive health.

My take-home summary of all this research is that it is good to be physically and mentally active. The details of what type of activity don’t seem to matter much, when it comes to mental activity it is best to challenge yourself. Do something new, and work your brain in new ways. There is no magic in any particular task or game, but there is a preliminary suggestion that activity which engages executive function may be particularly useful.

Other factors

Are there other factors that could also be responsible for the decline in dementia prevalence? Probably, but there are so many possible factors at present we cannot nail down which ones are important.

Overall good health is likely a factor. This is an easy recommendation to make, because there are obvious wide-ranging advantages to overall good health. If it also reduces dementia risk, that’s just the icing on the cake. So, don’t smoke, get plenty of sleep, drink in moderation, exercise regularly, treat your chronic conditions like hypertension and diabetes, and take good care of yourself.

What about nutrition? Generally good nutrition is always a good idea, but what about specific supplements? Vitamin E and C (the anti-oxidants) get a lot of attention, but a 2013 systematic review concluded:

Overall, findings do not consistently show habitual intakes of dietary antioxidants are associated with better cognitive performance or a reduced risk for dementia. Future intervention trials are warranted to elucidate the effects of a high intake of dietary antioxidants on cognitive functioning, and to explore effects within a whole dietary pattern.

The evidence, however, remains mixed and I would say this is still a bit of an open question, but clearly there is no home-run here. Other specific nutrients, like folic acid, B12, and B6, also have not shown a consistent benefit when taken routinely.

However, elevated homocysteine levels does appear to be a risk factor for vascular disease and Alzheimer’s disease, and these B vitamins reduce homocysteine levels. Some researchers believe that current studies are inadequate because they mix in subjects who are healthy and don’t need B vitamins, which is a fair point.

At present, at the very least, older patients should be routinely tested for B vitamin and homocysteine levels and supplemented appropriately. Targeted supplementation may be better than routine or blind supplementation. It is easy, for example to oversupplement and have B6 levels that are too high, and even toxic.

Best advice: stay active, eat well, like your doctor tells you to

It is somewhat reassuring that dementia prevalence has declined in the US and other developed countries. Dementia remains a serious public health issue and anything to reduce its burden is welcome.

The recent study only provides evidence that years of education seem to have a protective effect, but this is also not the whole picture.

The best current advice for those who wish to minimize their dementia risk is to remain physically and mentally active, have overall good nutrition, and overall good health. There does not appear to be any magic bullet.


Posted by Steven Novella

Founder and currently Executive Editor of Science-Based Medicine Steven Novella, MD is an academic clinical neurologist at the Yale University School of Medicine. He is also the host and producer of the popular weekly science podcast, The Skeptics’ Guide to the Universe, and the author of the NeuroLogicaBlog, a daily blog that covers news and issues in neuroscience, but also general science, scientific skepticism, philosophy of science, critical thinking, and the intersection of science with the media and society. Dr. Novella also has produced two courses with The Great Courses, and published a book on critical thinking - also called The Skeptics Guide to the Universe.