US dementia rates drop even as population ages; what gives?

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The proportion of older Americans living with dementia fell between 2000 and 2012, according to a new study. The exact reasons for the drop aren’t clear yet, researchers say.

“If we can do a better job of pinpointing those (reasons), not only will we be able to estimate future burden better but (we could) focus on intervening factors that have strong impact on dementia risk,” said study leader Dr. Kenneth Langa, from the University of Michigan in Ann Arbor and the VA Ann Arbor Healthcare System.

Dementia impairs patients’ memory and cognitive skills. The number of people with dementia is expected to triple by 2050 due to an aging population, the researchers write in JAMA Internal Medicine.

New study: proportion of older Americans living with #dementia fell between 2000 and 2012 Click To Tweet

Past research has suggested that some high-income countries may see a decline in dementia rates, however. In one study from Massachusetts, the annual number of new dementia cases fell by 20% over about three decades.

For the new study, reported by Reuters, Langa and colleagues analyzed data from a U.S. survey of people 65 years and older, including 10,546 people in 2000 and 10,511 in 2012. The prevalence of dementia in 2000 was 11.6%, compared to 8.8% in 2012.

The decline occurred despite an increase in heart health risk factors like high blood pressure and obesity between 2000 and 2012, the researchers write. They also report that more years of education was tied to a lower risk of dementia. The average length of education among participants increased from about 12 years in 2000 to about 13 years in 2012.

“The really important and optimistic conclusion you can take away from our study and some of the other studies is that there are things we can do as individuals and societies to reduce dementia risk,” Langa told Reuters Health.

The new report and previous studies suggesting a declining prevalence of dementia are encouraging, Ozioma Okonkwo and Dr. Sanjay Asthana write in an editorial accompanying the new study.

“The focus now should be on better understanding the factors that underlie this trend, and translating that knowledge into interventions that can reduce the risk of dementia for both individuals and the society as a whole,” write Okonkwo and Asthana, of the University of Wisconsin School of Medicine.

Langa’s team is trying to analyzed the factors associated with the falling dementia rates. Also, he said, it’s important to continue monitoring the prevalence of dementia, because the decline in rates may be halted or reversed due to increases in obesity and diabetes.

“We just don’t know if there may be an uptick of dementia risk going forward because of those other changes,” said Langa.

Steve’s Take:

This new national study is important in finding that, after adjusting for age, Americans 65 and older are less likely to get dementia than in the past. The report, published in the Journal of the American Medical Association (JAMA), confirms previous regional studies in the US as well as recent research in Europe.

The reasons for this decline in prevalence of the many dementia-related diseases are complicated, but may be related to higher educational levels. Whatever the cause, the news is positive as the prior findings needed this additional validation, and now we’ve got it.

Bear in mind that the research, led by Dr. Kenneth Langa of the University of Michigan, does not mean that fewer Americans will suffer from this disease. Indeed, as more of us reach old age, more of us will suffer from various forms of severe cognitive impairment. But the odds that any individual older adult will get dementia are getting longer.

In 2000, about 11.6% of all those 65 and older had dementia. By 2012, that had fallen to about 8.6%, a decline of almost one-quarter–great news. Similarly, in 2012, about 19% suffered from less severe cognitive impairment, down from 21% twelve years earlier–a smaller decline, but still important.e

Even among the so-called “old old,” the decline in dementia risk was noticeable–falling from 34% in 2000 to a bit below 30% in 2012. The study is adjusted for age and sex and was based on a large national sample of older adults called the Health and Retirement Study.

The study looked at all forms of dementia, not just Alzheimer’s Disease, the most common. Indeed, much of the decline may have occurred with vascular–or stroke-related–dementia.

So what’s going on? These authors, like the European researchers, are not sure, says Forbes. But the decline in dementia rates seems somehow connected to a rise in educational attainment: The more education you have, the less likely you are to have dementia after age 65. Okay, but what does that have to do with anything?

Here’s the explanation.

Lifelong education and cognitive stimulation (sometimes called cognitive reserve) may prevent or delay the onset of dementia. Or it may be that better-educated people have healthier lifestyles or get better health care.

The other fascinating finding is that the decline in the prevalence of dementia comes even as older adults report higher levels of obesity and diabetes, diseases that often increase the risk for strokes.

However, the researchers also found that this population may be doing a better job managing these conditions, thus reducing the chances of those dementia-causing strokes. It is, as the authors acknowledge, very complicated.

So where do we go from here? The general trend seen for a decade will continue, the enlightened suggest. As advances in public health and medical technology help us live longer, more of us will live long enough to suffer severe cognitive decline.

Remember, about 30% of those 85+ still will get a dementia-related condition. But for reasons we still don’t clearly understand, the chances of any one of us avoiding one of these diseases are improving, and improving pretty dramatically.

Yes, there are caveats all over the place as scientists are wont to do in order to keep hopes from becoming unrealistic, then dashed. And, of course, to protect themselves from, oh, I don’t know…litigation?

Steve's Take: Improved chances of avoiding #dementia is great news! Click To Tweet

Still, I don’t know about you, but after news last week that Eli Lilly’s highly anticipated, experimental Alzheimer’s treatment bombed, I’m elated.

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