U.S. Dementia Rates Fall

For the past 10 years, evidence has been building that the risk of Alzheimer’s is declining in high-income countries. The newest report comes from the most diverse sample yet. Scientists led by David Weir and Kenneth Langa, University of Michigan, Ann Arbor, reported November 21 in JAMA Internal Medicine that between 2000 and 2012 the prevalence of dementia in the United States fell a stunning 24 percent among people older than 65. The data come from the Health and Retirement Study (HRS), which includes people from different racial and socioeconomic backgrounds. It may mean a million fewer dementia cases over the next two or three decades than were projected, Langa said.

“This could have huge public health and policy implications,” he told Alzforum. Langa said that while the number of people with dementia will undoubtedly increase significantly over the next 20 or 30 years as the population ages, the total burden might be smaller than expected.

Outside scientists praised the work, saying it was in line with similar findings from other longitudinal observational studies. “A 25 percent reduction is a pretty big effect,” said Lon Schneider, University of Southern California, Los Angeles, who was not involved in the work. “If you saw this kind of an effect with a drug, you’d be talking about a cure.”

The studies from the United States, United Kingdom, and Europe that have reported declines in incidence and prevalence of dementia in recent decades all draw their samples from mostly white populations, often from geographically distinct locations (for a review, see Langa et al., 2013; May 2013 news). In an effort to survey a more representative cohort, Langa and colleagues relied on the HRS, which samples from the entire U.S. population. Nearly a quarter of the volunteers were minorities—14 percent identified as black, 8 percent Latino, and 2 percent as other non-Caucasian groups. HRS scientists had previously reported a decline in dementia risk between 1993 and 2002 (Langa et al., 2008). In this study, the researchers wanted to see if that trend continued into the current decade.

The HRS collects data on cognitive health through its biennial survey. That survey contains items adapted from the Telephone Interview for Cognitive Status (TICS), such as immediate and delayed free recall, serial seven subtraction, and backward count tests. If participants are unable or unwilling to take those tests, researchers ask a spouse or adult child about the volunteer’s memory. People are then classified as having either dementia, cognitive impairment without dementia, or normal cognition. In the current study, the researchers compared 10,546 survey responses from the year 2000 with 10,516 from 2012. Each cohort averaged age 75. The 2012 group had a higher proportion of people who were older than 85 and averaged one extra year of education compared with the respondents from 2000.

Despite being older, the prevalence of dementia in the 2012 cohort was 8.8 percent, compared with 11.6 percent in 2000, a relative decline of 24 percent. Likewise, the percentage of those with cognitive impairment fell from 21.2 percent to 18.8. Linear regression modeling suggested that better education and higher net worth best explained the lower risk of dementia. Advanced age, minority status, and a history of stroke or diabetes increased the odds of getting dementia. Being overweight or obese appeared to be protective, a result that seems to agree with a recent controversial report that extra pounds in old age are good for memory (Apr 2015 news). 

The falling incidence supports the cognitive reserve hypothesis, which posits that education and cognitive stimulation early in life can help guard against dementia down the road, the authors wrote (Jun 2014 news). However, they pointed out that genetic factors can also underlie education levels, and that better-educated people have healthier lifestyles, more stimulating jobs, and better health care, all of which could influence dementia risk. In addition, the authors noted that obesity, diabetes, hypertension, and heart disease were on the rise in this group over the same time period. A declining rate of dementia at the same time could mean that better control of these cardiovascular risk factors lowers dementia risk.

“Even if we don’t have breakthrough with a medication or other intervention, it appears there are things we as individuals and as a society can do to decrease dementia risk,” said Langa. Furthering education and improving control of cardiovascular risk are obvious starting points, but other factors such as better nutrition and reduced environmental pollution could also come into play, Langa said. The authors acknowledged that the study was based on self-reports that could have led to misdiagnosis, especially where participants suffered from memory loss. New funding from the National Institute on Aging will enable them do more detailed cognitive assessments in future studies, they said.

The growing consensus of a potential decrease in dementia prevalence is encouraging, wrote Ozioma Okonkwo and Sanjay Asthana, University of Wisconsin School of Medicine and Public Health, Madison, in an accompanying commentary. “The focus now should be on better understanding the factors that underlie this trend.”

Carol Brayne, University of Cambridge, U.K., agreed. “We need to understand the influences that have led to these changes and ensure that policy makers are aware that practices begun many decades ago seem to be playing out now,” she wrote to Alzforum. “Current policies should be assessed for their potential to maintain and continue such positive trends,” which are likely different in lower- and middle-income countries, she added. Langa said his group will next collaborate with scientists in England, Mexico, India, and China to try to understand risk factors and trends in dementia in diverse regions of the world.

While the message is optimistic, Schneider cautioned that scientists should not be lulled by the finding. “Just because we see this trend now doesn’t mean it is going to continue,” he said. “We might be maximizing what can be done environmentally and it might flatten out.”—Gwyneth Dickey Zakaib

Comments

  1. This study adds to the wave of evidence suggesting a decline in the risk of dementia in high-income countries in the past 25 years. This new study is important because it is based on a nationally representative sample from the United States. We had two studies suggesting a decline in the incidence (or risk) of dementia in the United States, one in Framingham, Massachusetts, and one in Olmsted County, Minnesota. Incidence is a more direct measure of risk than prevalence because prevalence is influenced by incidence and survival. However, the Framingham and Olmsted County studies were based on local communities with limited representation of demographic minorities. Thus, the study by Langa et al. provides useful complementary data.

    The study was well-conducted and well-described. The limitations are clearly recognized (e.g., use of short cognitive scales without a clinical examination; changes over time in the percent of use of proxy respondents; use of self-reported data).  

    Three important observations were made:  

    1) The prevalence declined even though the cardiovascular risk profile worsened (e.g., prevalence of hypertension, diabetes, and obesity).  These findings suggest that the increase in prevalence of cardiovascular risk factors was probably counterbalanced by an improvement in treatment (better treatment of hypertension and diabetes).  The increasing trends in late-life obesity and overweight need further study.  

    2)  The relative decrease over 12 years was 24.1 percent for dementia (2.8/11.6 percent) and 11.3 percent (2.4/21.2 percent) for cognitive impairment-no dementia (similar to mild cognitive impairment). The relative decline appears to be greater for dementia than for cognitive impairment-no dementia. This difference, if confirmed, could be useful in interpreting the trends.    

    3) A large segment of the decline remains to be explained. The OR of 0.69 (after age and sex adjustment) only increased to 0.82 after accounting for all of the factors considered. Therefore other yet unknown factors must have played a role.
     

    View all comments by Walter A. Rocca
    • User Profile Image Sudha Seshadri
      Glenn Biggs Institute of Alzheimer's, UT Health
    • Posted:

    This paper from the Health and Retirement study estimates the prevalence of dementia in 2012 compared to 2000, finds a decrease in dementia prevalence, and tries to examine possible causes.

    The strengths of the study are the large samples of ~10,000 persons in each wave and a more diverse sample compared to the Framingham, CFAS, and Rotterdam studies, which included predominantly Caucasians. The findings were similar to those we observed in the Framingham Heart Study (FHS) with lower age-adjusted prevalence of dementia and increased education in more recent years. Further, risk of dementia associated with certain conditions (here, heart disease-stroke was not specifically assessed) was lower in the second epoch than the first.

    One limitation of the study is that a brief cognitive battery was used to categorize persons as possibly having dementia, although this battery was validated against a more detailed assessment in the ADAMS subsample. Further, data on whether or not someone had vascular risk factors was determined only by history and not by direct evaluation. Finally, the survey methods changed between 2000 and 2012, with more home visits and proxy interviews in the second phase. However, the last should, if anything, be expected to increase the percentage of persons with true dementia who were identified as being demented (increased sensitivity). 

    Overall, the HRS data reinforce the FHS findings that age-specific risk of dementia may be decreasing and that changes in vascular risk factors did not explain this change. 

    View all comments by Sudha Seshadri

  3. This analysis comes from a nationally representative and highly respected study that has added measures relevant to dementia identification in recent years. It is very carefully conducted research. These findings are very much in line with findings from another highly respected U.S. study (Framingham). Whilst its design is different from our own in the U.K., the findings are very similar to ours in the Cognitive Function and Ageing Study I and II published a couple of years ago, and also are in line with some of those we synthesized in the European review of studies across time. This study suggests, again, that a substantial drop in prevalence across time has occurred, such that at any given age an older person now is less likely to meet criteria for dementia than a similarly aged person a decade and more ago, leading to a reduction in age-specific prevalence. The possible reasons are not fully known but, using the wide and robust evidence on known risk for dementia as well as changes in profiles of population health (dramatic reductions in stroke and heart attacks), it seems likely that improvements across the whole life course, including education, nutrition, reduction in smoking, better management of vascular risk and diseases, all are likely to have made a contribution.

    In other words there have been major intergenerational influences on health, and dementia is not exempt from such changes despite its very close association with age. The underlying neurobiology of dementia is likely to be a complex interplay of age, genetic risk for specific protection or risk trajectories (large, small, and interactions), life course risk/protection behaviors such as education and smoking, compensatory or reserve factors, and other exposures. We know that education is associated with compensation so that more people with higher education given a particular level of Alzheimer’s-type neuropathology can die without developing dementia, compared to those with lower levels of education. Thus we continue to learn the lesson that late-life dementia is not straightforward, nor is it likely to be amenable to simple solutions. We need to understand the influences that have led to the changes observed and also to ensure that policy makers who can influence the life course of the population's brain health are aware that policies and practice many decades ago seem to be playing out now, and current policies should be assessed for their potential to maintain and continue such positive trends.

    These findings are not likely to be the same in lower- and middle-income countries where life course experiences are very different across the generations.  

    View all comments by Carol Brayne

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References

News Citations

  1. Dementia Incidence Said to Drop as Public Health Improves
  2. Pound-for-Pound Protection: Does Obesity Guard Against Dementia?
  3. A Life of Cognitive Enrichment May Fend Off Dementia. But How?

Paper Citations

  1. Larson EB, Yaffe K, Langa KM. New insights into the dementia epidemic. N Engl J Med. 2013 Dec 12;369(24):2275-7. Epub 2013 Nov 27 PubMed.
  2. Langa KM, Larson EB, Karlawish JH, Cutler DM, Kabeto MU, Kim SY, Rosen AB. Trends in the prevalence and mortality of cognitive impairment in the United States: is there evidence of a compression of cognitive morbidity?. Alzheimers Dement. 2008 Mar;4(2):134-44. PubMed.

Further Reading

Papers

  1. Matthews FE, Arthur A, Barnes LE, Bond J, Jagger C, Robinson L, Brayne C, . A two-decade comparison of prevalence of dementia in individuals aged 65 years and older from three geographical areas of England: results of the Cognitive Function and Ageing Study I and II. Lancet. 2013 Jul 17; PubMed.
  2. Schrijvers EM, Verhaaren BF, Koudstaal PJ, Hofman A, Ikram MA, Breteler MM. Is dementia incidence declining?: Trends in dementia incidence since 1990 in the Rotterdam Study. Neurology. 2012 May 8;78(19):1456-63. PubMed.
  3. Qiu C, von Strauss E, Bäckman L, Winblad B, Fratiglioni L. Twenty-year changes in dementia occurrence suggest decreasing incidence in central Stockholm, Sweden. Neurology. 2013 May 14;80(20):1888-94. PubMed.
  4. Manton KC, Gu XL, Ukraintseva SV. Declining prevalence of dementia in the U.S. elderly population. Adv Gerontol. 2005;16:30-7. PubMed.

Primary Papers

  1. Langa KM, Larson EB, Crimmins EM, Faul JD, Levine DA, Kabeto MU, Weir DR. A Comparison of the Prevalence of Dementia in the United States in 2000 and 2012. JAMA Intern Med. 2017 Jan 1;177(1):51-58. PubMed.

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