Megan Brooks

July 15, 2014

COPENHAGEN, Denmark ― New data suggest fewer people in high-income countries, including the United States and those in Europe, are developing Alzheimer's disease (AD).

Experts believe higher education levels and more aggressive treatment of cardiovascular disease may be behind this trend.

The data were presented here at a press briefing at the Alzheimer's Association International Conference (AAIC) 2014.

The global prevalence of AD is projected to increase in the coming decades as the population ages. Current estimates suggest that about 4.2 million adults in the United States have dementia and that the attributable economic cost of their care is about $200 billion annually.

Worldwide, an estimated 44.3 million people had dementia in 2013. The total number is expected to double every 20 years, owing to the aging of populations, especially in low- and middle-income countries.

Yet recent studies from developed countries suggest a decline in incidence or prevalence of dementia (or both), Kenneth Langa, MD, PhD, of the University of Michigan and the Veterans Affairs Ann Arbor Center for Clinical Management Research, reported during the briefing.

He noted that at least 5 recent population-based studies of dementia incidence or prevalence reveal a declining age-specific risk in the United States, Rotterdam, Stockholm, and England.

Although the current and projected impact of AD and dementia on patients, families, and economies around the world is "very sobering," recent studies provide "what looks like optimistic news in terms of declines in the individual risk of getting [AD] or dementia over the last 20 years in high-income countries," said Dr. Langa.

A number of factors, especially an increase in educational attainment and more aggressive control of cardiovascular risk factors, including diabetes, hypertension, and hypercholesterolemia, "may be leading to improving 'brain health' and declining age-specific risk of AD and dementia in countries around the world," he added.

Whether this "optimistic trend" will continue in the face of rising levels of obesity and diabetes, and whether it is also true in low- and middle-income countries, are "key, unanswered questions," said Dr. Langa.

The answers to these questions will have "enormous implications for the extent of the future worldwide impact of AD and dementia in the decades ahead," he noted.

Framingham Data

Temporal trends in dementia incidence in the Framingham Heart Study during roughly the past 3 decades also point to declines in new cases of dementia, reported Claudia L. Satizabal, PhD, of Boston University School of Medicine, in Massachusetts.

She and her colleagues defined 4 nonoverlapping 5-year time windows (epochs) beginning in 1978; they studied new cases of dementia among initially dementia-free participants aged 60 years and older and estimated the age-adjusted incidence of dementia in each epoch.

The results show a "progressive decrease" in the incidence of dementia, Dr. Satizabal told those attending the briefing.

For example, compared with the first epoch in the late 1970s, there was a 22% reduction in new cases of dementia in the second epoch in the late 1980s, followed by a 38% reduction and a 44% reduction in the third and fourth epochs, respectively.

The reduction was strongest in the "youngest old," those between 60 and 69 years of age. The age at dementia onset also "shifted" during the years to older individuals, Dr. Satizabal noted. The researchers found that the decrease in dementia incidence was greatest in women across all epochs, whereas men showed a more gradual decrease over time.

"Interestingly," Dr. Satizabal said, a consistent reduction in the incidence of dementia across all time periods was seen in participants with at least a high school education, whereas this reduction was not observed in those without a high school diploma.

The Framingham data also point to a substantial improvement in the management of vascular risk factors during the study period, as well as a decline in smoking, heart disease, and stroke. However, an increasing trend in obesity and diabetes was seen in this population.

"This leads us to cautious optimism that some cases of dementia may be preventable. However, one of the limitations of this work is that the Framingham sample is largely of European descent. Additional studies are needed in populations of different racial and ethnic backgrounds," Dr. Satizabal said.

Picture in Developing Countries

However, other data reported at the conference suggest that the incidence and prevalence of AD in developing countries such as Colombia and in large regions of Asia and Africa may be severely underreported and may be rising.

For example, in his presentation, Dr. Langa noted that recent data from China suggest that the number of dementia cases in China in 2012 was 9.2 million, significantly higher than the prior estimate of 5.4 million. Also, the age-specific risk for dementia in China increased between 1990 and 2010.

"It could be that lower levels of education and other risk factor trends in China explain this," said Dr. Langa.

"The good news is that recent trends in developed countries in Europe and the US suggest that reduction and possibly even prevention of Alzheimer’s disease might be possible ― but, at the same time, we must acknowledge the growing worldwide epidemic," Maria Carrillo, PhD, Alzheimer’s Association vice president of medical and scientific relations, said in a statement.

"We must continue efforts to halt this terrible scourge that devastates families and economies," she added.

"According to new data reported at AAIC 2014, Alzheimer's and dementia incidence and prevalence in developing countries may be much higher than previously thought, and rising rates of obesity and diabetes pose an unknown but potentially serious threat to cognitive health throughout the world. Many questions remain, and the only way we can get the answers is through more research," said Dr. Carrillo.

The study by Dr. Langa and colleagues was funded by the National Institute on Aging. The study by Dr. Satizabal and colleagues was funded by the National Institutes of Health. The authors report no relevant financial relationships.

Alzheimer's Association International Conference (AAIC) 2014. Abstracts 42984 and 42865. Presented July 15, 2014.

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