Dementia study has good news: Prevalence declines even as population ages

“Better education and cardiovascular health may be key. This means hope for reducing risk through social determinants and lifestyle,” says Dr. Eric B. Larson

About 10 years ago, my colleague Dr. Ken Langa and I read some unusual findings about the prevalence of dementia among older Americans. Researchers at Duke University had been analyzing data from a sample of Medicare enrollees screened for age-related problems with thinking. Surprisingly, the prevalence of severe cognitive impairment had declined significantly between 1982 and 1999.

How could this be? We wondered. At a time when experts were predicting a demographic tsunami of baby boomers with age-related brain dysfunction, here was evidence that the storm was actually abating. Was this Duke discovery an anomaly? Could it be replicated in a larger study?

To find out, Ken and his team at the University of Michigan’s Institute for Social Research mobilized their Health and Retirement Study — a nationally representative, population-based longitudinal survey of older Americans. The initial results, published in 2008, surprised us by showing the Duke team had indeed gotten it right: Even as our population is aging, the proportion of older people with dementia is slowly declining.

Since then, other researchers in developed countries around the world have reported similar good news. This is despite increases in diabetes, high blood pressure, and obesity — problems thought to raise risk of dementia by interfering with blood flow to the brain.

And now, we have even stronger evidence that dementia prevalence is declining. In a study published in the November 21 JAMA Internal Medicine, we evaluated HRS trends among 21,000 people age 65 and older and found that in the year 2000, 11.6 percent met the criteria for dementia. But by 2012, only 8.8 percent did. What made the difference? We believe it’s education, because over that time, the average time a senior had spent in school rose from 12 years to 13 years. We also believe that better control of cardiovascular risk factors may have contributed to the improvement.

These findings are encouraging because they mean the advances our society has already made in education, health care, and reduction of cardiovascular risks such as smoking may continue to yield declining rates of dementia as baby boomers reach old age. The results also suggest that individuals of all ages can take steps today to build “cognitive reserve” — the brain power that that may prevent or delay age-related dementia. These steps include regular physical activity, eating a heart-healthy diet, and not smoking.

Our findings should also encourage communities to reduce disparities in social determinants of health — factors such as equal access to quality education, good health care, healthy foods, and opportunities for exercise. Doing so could help our society reduce the prevalence of dementia among all people while improving countless other aspects of health and well-being for the entire population.

In the meantime, our research teams will continue to learn more about ways to strengthen brain function and prevent cognitive dysfunction in in old age. At Group Health Research Institute, for example, our Adult Changes in Thought (ACT) study team will keep serving as a “living laboratory” to identify and reduce risks that lead to dementia. Our ACT study team was pleased to serve as a pilot site for Ken Langa’s ongoing work with the Health and Retirement Study. We’re looking forward to more collaboration in the future.

Eric B. Larson
Vice President for Research, Group Health
Executive Director, Group Health Research Institute

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