Listen to an interview with Kenneth Langa on the causes, trends, and policy ramifications of cognitive impairment and decline in the United States (16 minutes)
(March 2009) When some people reach older ages, they begin to lose their ability to reason and to remember. For at least one in every 12 elderly people, the decline in cognitive function is so severe they have difficulty performing the normal activities of daily living, and eventually, cannot live independently.
With continued population aging—the number of Americans ages 65 or older is projected to swell from around 41 million to 65 million over the next 15 years—the loss of cognitive function among some older Americans foreshadows a potentially enormous social and economic burden on individuals, families, communities, and the nation. The U.S. National Institutes on Aging Division of Behavioral and Social Research is funding research to find out more about declines in cognitive functioning among older Americans. What are the recent trends? What factors are associated with a faster or slower decline? The answers to these questions are relevant for policymaking in a wide variety of areas.
At a March 18 seminar in Washington, D.C., three researchers presented findings from their NIA-supported studies of cognitive impairment among the elderly.
'Brain Health' Determines Risk of Cognitive Impairment
Kenneth Langa, University of Michigan School of Medicine and Institute for Social Research, presented the results of an analysis using data from the national Health and Retirement Study (HRS). The HRS measures cognitive impairment through tests of memory recall, one symptom associated with cognitive impairment. Severe cognitive impairment may be diagnosed as dementia, and about 65 percent of dementia patients have Alzheimer’s disease. A survey can measure some symptoms associated with dementia, but cannot diagnose dementia in study participants.
Results from Langa's study show that cognitive impairment among Americans ages 70 or older declined between 1993 and 2002, from 12.2 percent to 8.7 percent. Langa and his colleagues attributed this improvement to several factors, including more effective treatment of stroke and heart disease—risk factors for dementia—and increased educational levels of older Americans. Average educational attainment for participants in the 2002 study was almost one year greater than for those in the 1993 study.
But Langa warned that other trends may adversely affect the brain health of Americans, especially rising obesity rates and a consequent increase in diabetes, which is also associated with declining cognitive function among older adults.
Education Builds Cognitive Reserve
Langa's finding that education "protects" the cognitive ability of older Americans, echoed in other studies, has been explained in several ways. Education may directly affect the brain's development—building a kind of "cognitive reserve" that older adults can draw on if they begin to suffer a decline in memory and reasoning ability. More educated people may be better able to develop techniques to compensate for their reasoning or memory problems, for example. People who have completed more education also tend to have healthier lifestyles, higher incomes, better health care, and more social opportunities—all associated with better brain health.
Although education and associated social and economic benefits can delay cognitive impairment in older Americans, they do not prevent it. Langa's research concluded that the decline in cognitive function occurred at older ages among the 2002 cohort of the HRS, but then progressed more rapidly. This "compression" of cognitive impairment into a shorter time-period confers more years free of impairment and fewer years with dementia.
The links between education and cognitive impairment were also a focus of the research reported by Dawn Alley at the March 18 seminar. Dawn Alley, University of Maryland School of Medicine, and her colleagues looked at factors associated with elderly adults’ transitions into and sometimes out of an impaired cognitive condition. People who suffered cognitive impairment because of a stroke, depression, and certain other conditions may recover some or all of their abilities, Alley pointed out.
More Educated Adults May Cope Better
Using the nationally representative AHEAD study (Assets and Health Dynamics Among the Oldest Old), Alley and her colleagues found a delay in cognitive impairment among more educated people, but warned that this could be somewhat misleading. More educated people may be better at hiding their impairment until it is more advanced: They are more adept at taking tests, for example, and thus may score higher on the study's test of cognitive function than a less educated person with the same cognitive ability. Also, the higher incomes that often come with higher education provide important advantages for impaired adults struggling to lead a normal life.
Alley and colleagues reported that older Americans tend to live about 1.5 years with severe cognitive impairment, whether in their 70s or their 90s. But the more-educated elderly live slightly shorter lives after diagnosis with cognitive impairment—one year on average. This conforms to the idea that education allows adults to delay the onset of cognitive impairment—or to mask its detection—but not to delay death.
In sum, education appears to protect people longer from the constraints on independent living caused by cognitive decline, although it cannot prevent eventual decline. And education later in life is beneficial: Alley reported results from a study by Stephanie Hatch and colleagues showing that education received after age 30 also boosts cognitive function.
Neighborhood Also Important
While individual characteristics like education and income are clearly related to brain health, the community environment is also important. Preliminary results from another study reported at the March 18 seminar by Kathleen Cagney, University of Chicago, found that people who live in neighborhoods plagued by crime, poor maintenance, and few community resources tend to be more likely to experience cognitive impairment than people in better neighborhoods. Cagney and her colleagues hypothesized that people in the poorer neighborhoods experience more stress—from fear of crime, for example—less community involvement, less access to medical facilities, and fewer opportunities for mental and physical stimulation (fewer libraries, walking paths, or fitness centers, for example).
But do such neighborhoods create or exacerbate cognitive impairment, or are people who live in these neighborhoods at a higher risk of impairment simply because they have low incomes and are less educated? Evidence from poorer ethnic neighborhoods offers a clue that community characteristics are important. Cognitive impairment was less common in low-income ethnic neighborhoods, perhaps because greater social cohesion in an ethnic enclave protects elderly residents against early cognitive decline. Previous research has shown that people with more social interaction and involvement have better physical and mental health.
Possible links between the social context of neighborhoods and cognitive decline have important implications as the number of elderly continues to grow. Efforts to address the mental health of the elderly will need to consider community, as well as individual, characteristics. For example, physical activity is important for controlling high blood pressure and other cardiovascular conditions associated with cognitive decline. How safe a neighborhood is, or is perceived to be, along with its noise levels and other characteristics may influence whether older residents venture out into the community and, hence, their levels of physical activity. From a public health perspective, investments in public safety programs or even noise abatement structures may have potential health benefits for the elderly.
As the number of elderly increase, so will the number of people with severe cognitive impairment. In light of these trends, research into what can delay or alleviate cognitive decline among the elderly offers valuable insight for future policies and planning.
Mary Mederios Kent is senior demographic editor at PRB.
For More Information
Kenneth M. Langa et al., "Trends in the Prevalence and Mortality of Cognitive Impairment in the United States: Is There Evidence of a Compression of Cognitive Morbidity?" Alzheimer’s & Dementia 4, no. 2 (2008): 134-44.
Agnès Livère, Dawn Alley, and Eileen M. Crimmins, "Educational Differentials in Life Expectancy With Cognitive Impairment Among the Elderly in the United States," Journal of Aging and Health 20, no. 4 (2008): 456-77.
Lisa L. Barnes, Kathleen A. Cagney, and Carlos F. Mendes de Leon, "Social Resources and Cognitive Function in Older Persons," in Handbook of Cognitive Aging, ed. Scott M. Hofer and Duane F. Alwin (Thousand Oaks, CA: Sage Publications, 2008): 603-10.
"One in Seven Americans Age 71 and Older Has Some Type of Dementia, NIH-Funded Study Estimates," NIH News, October 2007, accessed online at www.nih.gov/news/pr/oct2007/nia-30.htm, on March 27, 2009.
"Study Finds Improved Cognitive Health Among Older Americans," NIH News, February 2008, accessed online at www.nih.gov/news/health/feb2008/nia-25.htm, on March 27, 2009.