New Evidence that the Prevalence of Dementia is Declining

A new analysis of data from a database on persons aged 65 or older found that the prevalence of dementia went from 11.6 percent in 2000 to 8.8 percent in 2012, a decline attributed in part to an increase in educational attainment among the later-born group.

Researchers have long been warning about a coming tsunami of dementia as the population of older people grows, but a new study shows that there may be some bright spots in that forecast.

A United States study involving persons aged 65 or older found that the prevalence of dementia went from 11.6 percent in 2000 to 8.8 percent in 2012, a decline attributed in part to an increase in educational attainment among the later-born group. Improvement in treatments for cardiovascular risk factors such as diabetes might also explain the more encouraging numbers, though “the full set of social, behavioral and medical factors contributing to the decline in dementia prevalence is still uncertain,” researchers reported in the November 21 online edition of JAMA Internal Medicine.

The downward trend for dementia, which had likewise been documented in some other studies, occurred despite the fact that a greater percentage of older Americans were obese or had diabetes, or both, in 2012 compared to 2000 — factors that have been correlated in middle age with an increased risk for dementia. Diabetes continues to be a major risk factor for dementia in older persons, according to the new analysis, but being overweight or obese decreases the risk of dementia about 30 percent. That counterintuitive finding has turned up in other studies as well.

An editorial that accompanied the JAMA Internal Medicine study referred to the “obesity paradox” — “that lower BMI [body-mass index], usually deemed indicative of good health, might be associated with increased mortality and morbidity among elderly individuals.”

One possible explanation is that in the period just before or early during dementia onset, people may experience weight loss due to changes in taste, smell and appetite or other factors. In other words, keeping weight on may be sign of continuing good health.

The study’s lead author, Kenneth M. Langa, MD, PhD, professor of medicine at the University of Michigan and the Veterans Administration Ann Arbor Healthcare System, said the decline in the prevalence of dementia from 2000 to 2012 does not negate the fact that the number of cases of dementia, including Alzheimer’s disease, is still likely to increase significantly in the US and around the globe as the older population increases.

“I don’t think the study should be interpreted that the dementia problem is solved and is not important,” Dr. Langa told Neurology Today. “There will be a very large number of older people in the US and around the world over the next 20 years as baby boomers continue to turn 65 and the 85-plus population continues to grow.”

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