Are Dementia Rates Declining?

With an estimated 47 million people worldwide living with dementia as well as a rapidly aging population in most places, researchers and health agencies have long been warning of a "gray wave" as the number of new dementia cases triples over the next three decades. Given the resulting rise in socioeconomic costs to care for these additional dementia patients, health care systems worldwide are expected to be increasingly overwhelmed by the costs of dementia care along with all the other health care needs in an aging population.

But a recent study published in the journal Neurology suggests that this projected burden of dementia care may not be as dire as previous research has indicated. The study presents the results of a comprehensive research project, the Alzheimer Cohorts Consortium (ACC) examining thousands of individuals over the age of 65 between 1988 and 2015. Consisting of 9 cohort studies conducted in the United States, France, the Netherlands, Sweden, the United Kingdom, and Iceland, the ACC has collected data on over 49,202 participants (59 percent female), including demographic and medical data including type of dementia diagnosis. Overall, 4,253 of the study participants had been diagnosed with some form of dementia by 2015 and the incidence of new dementia diagnoses is steadily increasing with age.

Contrary to expectation though, the researchers found a 13 percent decrease in all-cause dementia per decade since 1998. A similar decrease turned up for cases of Alzheimer's disease alone with men showing a much higher decrease than women (24 percent vs. 8 percent). Based on these results, and assuming that this trend continues in Europe and North America over the next few decades, there may be 15 million fewer dementia cases than expected in high-income countries alone. If this same trend could be achieved worldwide, this could mean 60 million fewer new cases of dementia by 2040. Though these results seem to contradict earlier, much more pessimistic projections of future dementia cases, these time trends seem fairly robust over time and across different countries.

At present, there are no easy explanations for why this decrease seems to be happening. “This is a very important observation, not only in its own right but, of course, to find out the reasons for this decline,” says lead author Albert Hofman in a recent media interview. Hofman, who also chairs the department of epidemiology at the Harvard T.H. Chan School of Public Health, acknowledges that the true explanation for this decline is likely related to the overall improvements in medical care for older adults in developed nations in recent decades.

For example, given that cardiovascular factors can definitely increase the risk of dementia, medical advances to reduce these risk factors can likely improve brain health as well. Research has long suggested that hypertension and other cardiovascular complications can potentially damage small blood vessels leading to the brain. As a result, blood flow to the brain can be sharply reduced leading to the death of neurons. Changes to blood vessels throughout the body may also interact with other physiological mechanisms to cause increased presence of amyloid and tau proteins which can accumulate in the brains of people with Alzheimer’s and other forms of dementia.

But over the past few decades, more people than ever have been benefiting from improved cardiovascular risk management, including the use of statins and other medications to control high blood pressure, cholesterol, and inflammation. These medications, along with cardiovascular rehabilitation programs aimed at discouraging smoking as well as introducing other healthy lifestyle changes (including improved diet and exercise) have helped ensure a healthier life for many people who might otherwise have developed dementia. At the same time, unfortunately, we have also seen a sharp rise in diabetes and obesity in Western countries, two risk factors that Hofman warned “certainly has not helped” in curbing dementia.

Another possibility raised by Hofman is the greater access to education and other forms of mental stimulation that can help older adults keep their brains active. Though the available evidence is still limited, increased mental stimulation in the form of continuing education and related activities can help boost cognitive reserve, or the capacity of the brain to resist damage. Also known as brain reserve, studies have shown that this increased resistance to damage can play an important role in preventing cognitive deterioration in many dementia patients. In several landmark studies looking at the autopsied brains of elderly patients, factors such as increased brain weight, reduced neuron loss, and greater cortical development appear to play a strong role in helping seniors resist Alzheimer's disease pathology, at least partially.

Granted these predictions about future dementia risk, while optimistic, don't necessarily mean that we should all stop worrying about the future "gray wave" and its potential impact on health care. But it does suggest that proper medical care and staying active, both mentally and physically, may well help seniors live much longer, more productive lives.