At the Alzheimer’s Association International Conference 2014, held July 12-17 in Copenhagen, Denmark, researchers presented more evidence that the risk of dementia is nudging downward in developed countries. The data add to a slew of recent studies that report similar findings (see May 2013 news story). According to results in a U.S. cohort, the incidence of dementia has declined gradually over the past 40 years. In Germany, a similar trend cropped up on a shorter time scale, and dementia appeared to occur over a shorter time period at the end of life.

As with previous reports, researchers attributed this reduction to improved cardiovascular risk factors and higher levels of education in certain countries. In absolute numbers, these incidence declines will be overwhelmed by increases in dementia brought on by population aging and negative health trends such as diabetes, but still, the data might shed light on means of delaying or preventing the disease, they said.

“Worldwide dementia cases will likely grow significantly over the next 40 years, but a number of studies now suggest that the declining risk of dementia in high-income countries has moderated that growth,” said Kenneth Langa, University of Michigan, Ann Arbor. He agreed that education and cardiovascular treatment could be responsible. “Going forward, it will be key to understand how these trends are working in low- and middle-income countries.”

Claudia Satizábal, from the lab of Sudha Seshadri at Boston University School of Medicine, presented new data from the Framingham Heart Study, a longitudinal cohort based in Massachusetts. The researchers became curious when they caught wind of falling dementia rates in other studies. To see if their population showed similar tendencies, they examined cognitively normal participants aged 60 and older starting in the late 1970s. From baseline assessments in four time windows of five years each, Satizábal and colleagues assessed how many people had progressed to dementia five years later. Relative to the first cohort assessed, the second, third, and fourth cohorts (in the '80s, '90s, and 2000s, respectively) had 22, 38, and 44 percent fewer incident cases of dementia. That decrease was stronger for women, and showed up more often in those with at least a high school diploma. Moreover, the mean age of dementia onset rose steadily, from 80 in the earliest time window to 85 in the last. Over the same time period, the researchers observed declines in stroke, blood pressure, cardiovascular disease, and smoking in the studied population.

The Framingham study examined mostly Caucasian people, but Satizábal said upcoming data from other studies will examine whether these trends hold in more ethnically diverse populations. “Dementia projections still hold and are worrisome,” she said at a press conference highlighting her work. “However, our results offer cautious hope that perhaps some dementia cases might be preventable by better management of cardiovascular risk factors and also by making education more available for all.”

Other researchers found much the same over a shorter time frame. Gabriele Doblhammer, German Center for Neurodegenerative Disease, Bonn, presented 2007-2009 data from AOK, the largest public health insurance provider in Germany. Using 2009 values as a reference and looking back in time, Doblhammer found that the prevalence of dementia in people aged 75-84 had been 2 and 4 percent higher in 2008 and 2007, respectively. This suggested a gradual decline in prevalence, the proportion of cases in a given age bracket each year. This effect, too, was strongest for women. The number of new dementia cases, i.e., the incidence, also dropped—2007 levels exceeded 2009 levels by 11 percent.

At the same time, mortality increased in people with dementia, especially women. That is actually good news, Doblhammer said, because it implies that new dementia cases are diagnosed at progressively older ages, and people spend less time with the disease. “This suggests that healthy life expectancy expanded, while the time with dementia became shorter,” said Doblhammer. She added that although the data contain no reasons for the shift, she also suspects education and cardiovascular risk factors.

Martin Prince, Kings College London, U.K., called the findings good news. “Incidence is happening later in life, closer to the time of natural death, therefore survival is shorter and we have compression of the time spent with dementia,” he said. However, trends look different in developing countries. Prince emphasized published data from China, where rising obesity, diabetes, and smoking is expected to compound huge increases in dementia brought on by shifting demographics (see Jun 2013 news story on Yang et al., 2013). “Population aging is happening much more rapidly in low- and middle-income countries,” he said. Therefore, health trends there will dominate global dementia levels.

Neil Buckholtz, National Institute on Aging, Bethesda, Maryland, pointed out that health gains in developed countries are likely to be undermined by rising rates of obesity and diabetes. “I’m not sure which trend will prevail,” he said. Population aging will still lead to many more cases of dementia, and they will be accompanied by a staggering price tag. “It’s hard to imagine how countries are going to deal with these costs,” Buckholtz said.—Gwyneth Dickey Zakaib

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References

News Citations

  1. Dementia Incidence Said to Drop as Public Health Improves
  2. Prevalence of Dementia, AD, in China Eclipses Predictions

Paper Citations

  1. . Rapid health transition in China, 1990-2010: findings from the Global Burden of Disease Study 2010. Lancet. 2013 Jun 8;381(9882):1987-2015. PubMed.

Further Reading