Dementia Rates Declining

Pauline Anderson

February 10, 2016

There's more evidence pointing to a decline in the incidence of dementia. New research using data from the Framingham Heart Study shows that even with increasing obesity and diabetes rates, and with an aging population, the incidence of dementia has progressively declined by approximately 20% every decade over a 30-year period, although the decline was limited to those with at least a high school education.

The results represent "cautious hope" that some cases of dementia might be preventable or at least delayed, lead study author, Claudia Satizabal, PhD, instructor, neurology, Boston University School of Medicine, Massachusetts, told Medscape Medical News.

Their results are published online February 10 in the New England Journal of Medicine.

Dr Claudia Satizabal

The Framingham Heart Study is a community-based longitudinal cohort study begun in 1948. The original cohort included 5209 residents of Framingham, Massachusetts. In 1971, 5214 offspring of the original cohort and their spouses were enrolled in an offspring cohort.

Cognitive status has been monitored in the original cohort since 1975. Since 1981, participants have been assessed at each examination using the Mini-Mental State Examination (MMSE).

The offspring cohort has undergone similar monitoring. They answered a subjective memory questionnaire in 1979, have undergone serial MMSEs since 1991, and have taken a 45-minute neuropsychological test every 5 or 6 years since 1999.

A dementia expert panel reviewed every case of possible cognitive decline and dementia. Panel members determined whether a participant had dementia, as well as the dementia subtype and date of onset.

Researchers looked at four overlapping "epochs." The first, 1977 to 1983, represented the baseline examination period; the second epoch was 1986 to 1991; the third epoch, 1992 to 1998; and the fourth epoch, 2004 to 2008.

For each epoch, the researchers included participants 60 years of age or older who were free of dementia at the start of the epoch. More than 2000 participants contributed data for each epoch.

The researchers compared the incidence of dementia across the epochs, adjusting for sex and age at entry. For each epoch, they reported the 5-year cumulative hazard ratios (HRs), which represent the cumulative incidence of dementia per 100 persons.

There were 371 cases of dementia, with a trend over time to an increasing mean age at diagnosis.

Compared to the first epoch, the incidence of dementia declined by 22% during the second epoch (P = .09), by 38% during the third epoch (P = .001), and by 44% during the fourth epoch (P < .001).

Table. Five-Year Age- and Sex-Adjusted Cumulative Risk for Dementia by Epoch

Epoch HR (95% Confidence Interval)
Epoch 1 3.6 (2.9 - 4.4)
Epoch 2 2.8 (2.2 - 3.5)
Epoch 3 2.2 (1.8 - 2.8)
Epoch 4 2.0 (1.5 - 2.6)

 

On average, since 1977, the incidence of dementia has declined 20% per decade (hazard ratio, 0.80; 95% confidence interval [CI], 0.72 - 0.90).

Much of the decline in the incidence of dementia was due to less vascular dementia, which might be explained by better control of stroke risk factors. The study found an increasing benefit from use of antihypertensive medication and a decreasing effect of cardiovascular events on the risk for dementia.

However, the decline in the incidence of Alzheimer's disease was not significant (P = .052), probably because of lack of statistical power.

The researchers found no evidence to suggest that the interaction between epoch and APOE ε4 status, age, or sex affected temporal trends in the incidence of dementia.

Only in Graduates

However, the interaction between epoch and educational level had a significant effect (P =.03). The study showed that the decline in the incidence of dementia was limited to those who finished high school, with an average decline in risk per decade of 23% (HR, 0.77; 95% CI, 0.67 - 0.88).

"The declining trend was only seen in people with at least high school diploma, not in those who didn't have a high school diploma," said Dr Satizabal. However, she added that over time fewer people hadn't finished high school, so by the final epoch, the group without a high school education was "very small."

She also noted that participants with a higher education tended to have better vascular health; for example, they smoked less, had less diabetes, and had better control of blood pressure.

The new results suggest that "we're doing something right in terms of primary and secondary prevention," said Dr Satizabal. "This study shows that there's something we can do to actually perhaps delay the disease or prevent some cases," which can be translated into public health policies, she said.

But while the results "are very positive," it's important to remember that people are living longer, said Dr Satizabal. "Baby boomers are aging and the population who will be elderly is going to be very large. That will translate into a higher prevalence of dementia, even if we have a deceasing incidence. So we still need to be very vigilant and aware, and continue research."

She also stressed that low- to middle-income countries are seeing a rise in vascular risk factors that will add to their dementia burden. Some studies suggest that the dementia prevalence in these regions has been underestimated, she said.

A limitation of the study was that it didn't examine the effects of risk factors for dementia, such as diet and physical activity, as possibly affecting the dementia trend.

Triumph and Catastrophe

An accompanying perspective article noted that because trajectories of chronic disease incidence reflect complex interactions of many causal factors, "it will almost always be uncertain whether decreases will continue or reverse."

"Even if a dementia decline has begun, it might not last: the outcome depends on the balance of diverging trends" — including increases in obesity and diabetes.

The perspective was written by David S. Jones, MD, PhD, Department of Global Health and Social Medicine, Harvard Medical School, Boston, Massachusetts, and the Department of the History of Science, Harvard University, Cambridge, Massachusetts, and Jeremy A. Greene, MD, PhD, Division of General Internal Medicine and the Department of the History of Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland.

As with rates of coronary artery disease (CAD), which beginning in 1964 were reported to be declining, but for which future forecasts "continue to swing between narratives of triumph and catastrophe," narratives for dementia remain "similarly malleable," Dr Jones and Dr Greene write.

But with this latest study, "optimism about dementia is more justified than ever before," they said. "Even if death and taxes remain inevitable," dementia, as well as CAD and cancer, may not be.

However, they warned that cautious optimism should not become complacency.

"If we can elucidate the changes that have contributed to these improvements, perhaps we can extend them," they conclude.

Optimistic Note

Keith N. Fargo, PhD, director of scientific programs and outreach, Alzheimer's Association, pointed to the more limited decline in AD. "What you're probably seeing is primarily a reduction in vascular dementia, which is the second most common cause of dementia, and some decrease in Alzheimer's disease," he told Medscape Medical News.

Patients with plaques and tangles in their brain who also have "poor vascularity" in the brain may develop dementia earlier than if they didn't have that poor vascularity, said Dr Fargo.

"What this study says is that even for people with Alzheimer's disease pathology, controlling these cardiovascular risk factors is a good thing, but you're not going to get to zero incidence or zero prevalence unless you're able to do something about the plaques and tangles."

While he thought the study generally represents "good news" and points to the importance of education and controlling cardiovascular risk factors in preventing or delaying dementia, Dr Fargo outlined a number of "caveats."

One is that the results hold true only for those completing high school — although even here, there's "a note of optimism" in that people can be encouraged to pursue more years of formal education, said Dr Fargo.

Another is that while Framingham is "a wonderful study and we've learned a lot from it," participants are overwhelmingly white and not representative of the full diversity of US population, he said. "It remains to be seen whether these trends hold true in other groups."

Dr Fargo also noted that "countervailing trends" of increasing rates of obesity and diabetes "cause us great concern" and "have the potential to completely wipe out the positive benefits" seen with controlling cardiovascular risk factors.

"So it really is important to continue to sound the alarm bells," he said.

The study was funded by the National Institutes of Health. The authors have disclosed no relevant financial relationships.

N Engl J Med. Published online February 11, 2016. Abstract Perspective

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