While the global epidemic of Alzheimer’s disease continues to grow, new data on lower incidence in the “youngest old” from developed countries in Europe and the United States suggest the possibility of reducing risk and/or preventing the disease, according to the results of several research studies announced at the Alzheimer’s Association International Conference2014 (AAIC 2014) in Copenhagen, Denmark. Scientists suggest higher education levels and more aggressive treatment of cardiovascular disease may be key.
Pointing in the other direction, researchers reported at AAIC 2014 that incidence and prevalence of Alzheimer’s in developing countries such as Colombia, and large regions of Asia and Africa, may be severely underreported. They also raise questions about the effects of the growing incidence of obesity and diabetes in developed countries, both of which are associated with increased risk of cognitive decline and dementia.
For clarity following are the definitions of prevalence and incidence:
- Prevalence – the number or proportion of cases of a disease in a population. (ie., How many people have Alzheimer’s disease in the USA right now?)
- Incidence – the number of new cases of a disease in a population over a given time. (ie., How many new cases of Alzheimer’s are there this year in Denmark?)
“The good news is that recent trends in developed countries in Europe and the USA 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,” says Maria Carrillo, Alzheimer’s Association vice president of Medical and Scientific Relations. “We must continue efforts to halt this terrible scourge that devastates families and economies.”
“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,” Carrillo says.
There are hints in the literature that engaging in more challenging mental activities, such as higher levels of education or intellectually demanding occupations, may increase cognitive reserve and thereby reduce the risk of developing Alzheimer’s or another dementia.
Review of recent data suggests fewer new cases of Alzheimer’s in the United States and Europe
Worldwide prevalence of Alzheimer’s disease is projected to increase in the decades ahead as the planet’s population ages, but recently published studies from the United States, the Netherlands, Sweden, and England suggest a decline in incidence or prevalence of dementia (or both) in those countries, according to a review of recent research conducted by Kenneth Langa of the University of Michigan and the VA Ann Arbor Center for Clinical Management Research, and reported at a plenary session at AAIC 2014.
Langa observed from the studies that a number of factors, especially rising levels of education and more aggressive treatment of cardiovascular risk factors such as hypertension and high cholesterol, may be leading to improved brain health and consequent decline of numbers of new cases of Alzheimer’s disease and dementia in certain countries or regions of the world.
“Whether this 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,” says Langa. “The answers will have enormous implications for the extent of the future worldwide impact of Alzheimer’s disease and dementia in the decades ahead.”
Extent of dementia in Asia and Sub-Saharan Africa may be severely underestimated
In 2009, Alzheimer’s Disease International (ADI) published data on global prevalence of dementia based on a review of 154 worldwide studies and United Nations (UN) population projections. Alzheimer’s Disease International carried out an update on that data for the December 2013 G8 Dementia Summit in London, focusing primarily on new evidence from Asia and Sub-Saharan Africa, and presented the results at AAIC 2014.
Based on a meta-analysis of Chinese and Sub-Saharan African studies combined with the latest UN population projections, Alzheimer’s Disease International concluded that the 2009 estimates of worldwide Alzheimer’s disease were too low. Alzheimer’s Disease International now estimates that 44.35 million people in the world were living with dementia in 2013, significantly up from the earlier estimate of 36 million people living with dementia in 2010. They project that the number will rise to 75.62 million in 2030 — 15% higher than the 2009 estimate — and 135.46 million in 2050, which is 17% higher than the 2009 Alzheimer’s Disease International estimate.
Specifically in the two focus regions, the researchers found that dementia prevalence increased for East Asia from about 5% to about 7%, and in Sub-Saharan African regions from a range of roughly 2 to 4% to 4.76%.
“Dementia, including Alzheimer’s disease, is one of the biggest global health challenges facing our generation,” says Marc Wortmann, executive director, Alzheimer’s Disease International. “As more and better data becomes available, the effect we’ve seen is a reduction in the variation of prevalence between world regions.”
“In addition, newly available data suggests that the current burden and future impact of the global dementia epidemic has been underestimated, particularly for the Asia and Sub-Saharan Africa. Especially in light of these revised estimates, there is an urgent need to develop policies to face this disease in all countries of the world, and to enhance our efforts in finding a cure or treatment that can delay the onset of dementia,” Wortmann adds.
New sases of dementia decline over three decades in the Framingham Heart Study
At AAIC 2014, Claudia L Satizabal of Boston University School of Medicine and colleagues reported on the results of a study of dementia trends among participants in the Framingham Heart Study, an ongoing, long-term (since 1948), multi-generational cardiovascular health study of residents of Framingham, Massachusetts, USA, to which dementia tracking has been added since 1975.
Framingham Study participants undergo comprehensive assessments for cardiovascular risk factors every two to four years, and remain under intensive surveillance for dementia and stroke. Study researchers defined four non-overlapping five-year time windows (epochs) across the past three decades, each beginning with a baseline examination, and studied new cases of dementia among all dementia-free participants age 60 and older.
After adjusting for age at entry and gender, the researchers found that compared with the first epoch, the second epoch had a 22% reduction in new cases of dementia, the third had a 38% reduction, and the fourth had a 44% reduction. The reduction was strongest in participants between age 60 and 69.
The researchers found the decrease in dementia incidence was greatest in women across all epochs, while men showed a more gradual decrease over time. The decreasing trend in dementia incidence was true for individuals with a higher educational level, defined as having a high school diploma, whereas individuals without a high school diploma did not appear to benefit from this reduction.
During that 30-year time period, the researchers observed among the participants a substantial improvement in educational achievement, better management of blood pressure, higher levels of HDL cholesterol, and a considerable decline in smoking, heart disease and stroke across the same epochs. However, an increasing trend in obesity and diabetes was seen in this population.
“These reductions in age-specific rates of new cases of dementia in the Framingham Study participants might be partly explained by the beneficial trends we observed in educational attainment and heart health risk factors,” says Satizabal. “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.”
In Colombia, dementia and Alzheimer’s disease might be underestimated by up to 50%
To date, Colombia has had only one study, known as EPINEURO, which attempted to estimate the country’s dementia prevalence from representative samples of the population 20 years ago. Using updated population estimates and prevalence estimates published in the international literature, Yuri Takeuchi of Universidad Icesi (Colombia) and colleagues estimated the number of people with dementia, and especially Alzheimer’s disease, in Colombia by stage of the disease. The results were reported at AAIC 2014.
The researchers created three models for Alzheimer’s prevalence in the country, each using different projections for the proportion of people with mild, moderate, and severe disease, and different theoretical assumptions on the transitions between stages. They found that the number of people with Alzheimer’s in Colombia could be as much as 220,000 in 2015, and 260,000 in 2020. The scientists calculate that current estimates for Alzheimer’s disease and other dementias in Colombia might be too low by as much as 50%. (The prevalence estimate of dementia for Colombia in people over 65 used in the study was 6%, according to Takeuchi.)
“To our knowledge, this is the first attempt to model and estimate dementia prevalence by stage of disease in the developing world; it is certainly the first attempt in Colombia,” says Takeuchi. “The fastest growth in ageing is happening in developing countries such as Colombia. This has profound implications not only for older people themselves, but for their households, social and community infrastructure, and social policy. These estimations by stage of disease are key information for policymakers because both the social burden and social costs are substantially different depending on the stage of disease.”
Dementia in Germany declined between 2007 and 2009
Gabriele Doblhammer of the German Center for Neurodegenerative Diseases (DZNE) and colleagues conducted a study exploring short-term dementia trends in Germany, and reported the results at AAIC 2014.
The research is based on claims data from the largest public health insurance company in Germany which covers about one-third of the total population aged 50+ and more than half of the oldest-old. The data include complete records of the inpatient and outpatient services, including dementia diagnosis. The complete insured population of roughly five million people at risk of dementia and about 600,000 dementia cases was used to study the prevalence; a 2.5% sample was the basis for the incidence study.
The researchers found that between 2007 and 2009, the total number of people with dementia decreased significantly among German women age 74 to 85. Dementia prevalence in 2009 was 3.6% lower than in 2007 and 1.8% lower than in 2008. Over that period, new cases of dementia decreased significantly for both men and women.
According to the researchers, over the last decade there was reduction in new cases of cerebrovascular disease in Germany and a “better treatment of vascular risk factors such as high blood pressure, hypercholesterolemia, and diabetes mellitus.” Among the elderly, increasing levels of education and wealth also were observed.
“This was the first study to explore dementia trends in Germany,” says Doblhammer. “The ageing of the babyboomers and the increasing life expectancy will lead to more dementia cases in old age. It is necessary to explore the modifiable risk factors of dementia in order to prevent the occurrence of the disease. In addition, more research is needed whether the increasing obesity epidemic and related diseases, such as the metabolic syndrome, may counterbalance the positive trends we are observing today,” the researchers add.