Summary: The prevalence of dementia in older Americans seems to be decreasing. Whether or not researchers find new medicines to prevent dementia, higher levels of education and late-life activity might reduce dementia rates.
Much has been written about the coming “silver tsunami” and the expected “epidemic” of Alzheimer’s and other dementias. My conversations with eldercare professionals here on the west coast of Florida seem to confirm these predictions. But in the U.S. overall, the numbers suggest the situation might not be so dire.
Researchers at the University of Michigan recently analyzed data on cognitive impairment from the Health and Retirement Study, a large survey of older Americans. Along with his colleagues, Ken Langa, an Internist and Professor at the university, surveyed more than 7000 people over the age of 70 in 1993. They found 12.2 percent had cognitive impairment “consistent with dementia.” In their similar 2002 survey, that percentage decreased to 8.7, a relative decrease of almost 30 percent.
Dr. Langa, whose work focuses on the epidemiology and costs of Alzheimer’s and other dementias, is the lead author on another recent study suggesting the use of Medicare claims to calculate dementia prevalence and costs of related care results in overstatement of both.
These numbers are not much comfort to people already affected by dementia, but from a public health point of view, this is really good news.
Why the decline in dementia rates?
In the 2002 University of Michigan survey, people 70 and older were more highly educated and wealthier than those in the 1993 survey. Analysis showed that the combination of these trends contributed to the decline in dementia rates, the researchers say. It’s also possible that better treatment of stroke and heart disease risks (high blood pressure, for example) were helpful, they write.
The idea that education could contribute to a decrease in dementia may be related to the concept of cognitive reserve, or an ability to compensate for problems in the brain. In theory, education can increase cognitive reserve, which can delay the onset of dementia symptoms. Delaying the onset of dementia until closer to the end of life reduces the burden of care, of course.
The results of this study seem to support the cognitive reserve theory. Compared with the 1993 survey, people in the 2002 survey who did have cognitive impairment had a higher risk of death. This might mean they had delayed symptoms until close to the end of life.
A general increase in intelligence and longer work lives – two trends that may be related to education and wealth -- may also contribute to lower dementia rates.
Maybe we’re just getting smarter
As documented by a researcher named James Flynn, intelligence quotients (IQs) seem to be rising in many countries. Could higher intelligence in the overall population (which may increase “cognitive reserve”) contribute to lower rates of dementia? “Yes,” says Dr. Langa. “These two trends may both be related to increasing levels of education. The so-called ‘Flynn Effect,’ which describes the general increase in average IQ in the population over the last decades, may be related to increasing levels of education in later cohorts of adults in a similar way to what we hypothesized in our study for the decreasing risk of dementia over time due to increasing levels of education in later cohorts.”
Does putting off retirement help?
Other researchers at the University of Michigan have published data showing a link between early retirement and problems with memory and thinking. The percentage of older Americans still working has increased since 1990, even in those 70 and older. Could this trend also be contributing to the decreasing prevalence of dementia?
“That is definitely a possibility, but we did not test that specifically in our study,” says Dr. Langa. “This is still quite a complex relationship, so more research needs to be done to sort out the relationships among education, wealth, occupation, retirement age, and the risk of dementia.”
Will dementia rates continue to decline?
The apparent trend towards lower rates of dementia is encouraging, but it’s hard to say if it will continue. One reason is we don’t have a full understanding of how various social, economic and medical factors affect those rates.
For example, the net worth of many older Americans has decreased sharply in the last couple of years. Will this affect the prevalence of dementia?
“That's an interesting question,” says Dr. Langa. “I just don't think we know how the financial crisis will affect middle-age and older adults in the long-term. If the decrease in wealth causes some to have much higher levels of stress and manage their health problems worse (for instance, not taking their blood pressure medications), this might lead to a higher dementia risk over time. But if the financial crisis ends up causing some adults to stay in the work force longer, that might actually end up decreasing dementia risk through the pathways we discussed above. So I think it's plausible that the financial crisis might have an impact in different directions, or perhaps none at all.”
Education and engagement: better than drugs?
Advocacy organizations are calling for increased funding for biomedical research on Alzheimer’s. But should we also be asking for government policies to increase funding for education and for programs that encourage older Americans to work or otherwise stay active? Could these policies have the potential to reduce the burden of caring for people with dementia as much as future pharmaceutical treatments?
“It is hard to make sure-fire recommendations or predictions,” Dr. Langa says, “but I do believe that policies that encourage the widest possible access to education for children from all socioeconomic levels might be significantly more beneficial for population "brain health" (and health, in general) than future pharmaceutical treatments for dementia. Government policies that allow older adults to keep working at jobs they enjoy, or engaging in cognitively stimulating activities when they retire, would also be beneficial for the brain health of our population. Of course, the science and politics required to successfully expand childhood and adult education opportunities for all are not straightforward, but I do think that keeping these goals high on our political agenda could have wide-ranging benefits for the health of future generations.”