Decline in dementia rate offers ‘cautious hope’

By Beverly Merz

Harvard Health Blog

According to the Alzheimer’s Association’s 2015 Facts and Figures sheet: “The number of Americans with Alzheimer’s disease and other dementias will grow each year as the size and proportion of the U.S. population age 65 and older continue to increase. The number will escalate rapidly in coming years as the baby boom generation ages.”

Despite these alarming projections, a report from a recent issue of the New England Journal of Medicine (NEJM) offered a few words of encouragement. Researchers from the longstanding Framingham study found that the rate of dementia has declined over the course of three decades.

Framingham researchers had been studying more than 5,000 men and women since 1975. The participants had physical exams, including tests for dementia every five years. The researchers determined that the five-year rate of dementia was 3.6 percent between 1982 and 1986 2.8 percent between 1991 and 1996, 2.2 percent between 1998 and 2003, and 2.0 percent between 2009 and 2013. Moreover, the average age when dementia was diagnosed increased from 80 to 85 over the 30 years.

Do these results fly in the face of the Alzheimer’s Association’s predictions? Perhaps somewhat, according to David S. Jones, M.D., Ph.D., the A. Bernard Ackerman Professor of the Culture of Medicine at Harvard Medical School. In the same issue of NEJM, Jones and Jeremy A. Greene, M.D., Ph.D., of Johns Hopkins Medical School, note that a 2005 report based on data from the National Long-Term Care Surveys showed that severe cognitive impairment among Medicare recipients had decreased significantly between 1982 and 1999. Jones and Greene point out that this isn’t the first time that the rate of a major disease has started to decline before our eyes. As of 1964, even as coronary artery disease was projected to strike increasing numbers of older Americans in the future, heart attack deaths were starting to fall.

Explaining the falling rates of dementia

The decrease in the rate of dementia was attributed largely to two things that we have some control over — education and heart disease. The decline was registered only in high-school graduates, but they made up most of the Framingham participants. The rate of cardiovascular disease — including stroke, atrial fibrillation, and heart failure — was also falling during the study period years. In that sense, the results give further support to evidence that education, which may build up a “cognitive reserve,” protects against dementia — and that cardiovascular disease, which restricts blood flow to the brain, may promote it.

But even as rates of cardiovascular disease declined, rates of obesity and diabetes were beginning to creep up among the Framingham participants. Both are also risk factors for dementia, as well as for heart disease, and their continued rise could dampen or even reverse a decline in the dementia and heart disease rates.

Moreover, the overwhelming majority of Framingham participants are white and middle-class. Whether the results apply to people in other racial and ethnic groups and economic classes remains to be seen.

Can you prevent dementia?

As the Alzheimer’s Association predicts, the numbers of people with dementia may ultimately increase simply because people are living longer. At the same time, the Framingham researchers offer “cautious hope that some cases of dementia may be prevented or at least delayed.”

The Framingham results bolster the notion that what’s good for the heart is good for the head. If you’re pursuing a heart-healthy lifestyle — following a Mediterranean-style diet, getting the equivalent of 150 minutes of moderate exercise a week, managing your stress, and engaging with friends and family — you’re likely lowering your risk of dementia in the bargain, too.

(Beverly Merz is executive editor of Harvard Women’s Health Watch.)