On the heels of numerous reports indicating falling dementia incidence across the developed world, a new study from the Netherlands suggests the opposite. In the March 7 PLoS Medicine, researchers led by Emma van Bussel at the Academic Medical Center, Amsterdam, report a small but statistically significant rise in new dementia cases in the Dutch population, amounting to 2 percent per year for the last 23 years. This data came from an analysis of primary care records, meaning that it could reflect increased awareness or earlier diagnosis of the disease by physicians, rather than an absolute increase, the authors noted. Nonetheless, the findings suggest the overall societal burden of dementia remains high, even in the face of improved public health, van Bussel said.

In an accompanying editorial, Eric Larson at the Group Health Research Institute, Seattle, and Kenneth Langa at the University of Michigan, Ann Arbor, agree. “The real take-home message of this important paper is that Dutch general practitioners and their communities are seeing increasing numbers of older people diagnosed with dementia, adding to the burden of work for primary care practices in an aging society,” they wrote.

The data came from nine general practice registration networks scattered throughout the Netherlands, and comprised a representative population sample of more than 800,000 people 60 years or older. Between 1992 and 2014, doctors diagnosed 23,186 new cases of dementia in this group. Incidence rose throughout the time period, but most of the boost was driven by people over 75, with the lion’s share seen in the oldest group, those 85 or older. The overall incidence of dementia increased from about 5 cases per 1,000 person-years in 1992 to 7.25 in 2014. These rates are roughly similar to those seen in other studies in Europe and the United States, the authors note.

However, several recent studies have reported dramatic drops in new cases in the last four decades. For example, the U.S. Health and Retirement Study found a 25 percent decline in incidence in the 2000s, while the Framingham Heart Study calculated a 44 percent drop between the late 1970s to early 2010s (see Feb 2016 newsNov 2016 news). Other epidemiological studies have recorded declining incidence and prevalence across the United Kingdom and Europe (see Jul 2013 conference newsJul 2014 conference newsApr 2016 news). Most of these studies did not rely on primary care records. Instead, specialists assessed cognitive status of whole cohorts using diagnostic criteria and tests that remained consistent over time.

Why did the Netherlands study not see a drop in general practice records, then? Larson and Langa speculate that greater recognition of dementia by primary care physicians may have played the biggest role, but there could be other factors at work as well. Van Bussel noted that longer lifespans and better survival after cardiac problems may be contributing to the rise in dementia cases in the oldest old, who previously might not have survived long enough to develop the disease. In addition, because more of the Dutch elderly, even those with cognitive impairment, now remain in the community rather than living in nursing homes, as they had done in the past, they may contribute to a seemingly higher incidence of dementia in primary care records. Those records do not include data from nursing home populations. Another possibility is that the greatest drop in dementia cases due to improvements in cardiovascular health occurred in the 1970s and ’80s, the authors suggest, explaining the large dementia incidence decreases in these decades reported by the Framingham Study. In recent decades, negative trends toward obesity and diabetes may have offset these gains, they speculate.

Others concurred that the source of these data could have introduced bias, and that more studies are needed. “This very interesting paper illustrates the value of national GP [general practitioner] databases, as available in the Netherlands, and the caveats in replacing carefully collected epidemiological data with data abstracted from medical records,” Sudha Seshadri at Boston University wrote to Alzforum (see full comment below). “We all agree that the trends in dementia need to be studied in more populations,” she added.

Regardless of the trend in incidence, researchers express broad consensus that the overall dementia prevalence will continue to soar as populations age, and that lower-income countries will be hit particularly hard (see Jun 2013 newsAug 2015 newsOct 2016 news). In their annual facts and figures report released March 7, the Alzheimer’s Association estimates that two-thirds of the projected increase in the global burden of dementia will occur in low- and middle-income countries. Higher-income countries will not be spared, however. For example, the incidence will double in the United States by 2050 due to the aging population.

The Alzheimer’s Association report also emphasizes the high financial and societal cost of the disease. In 2017, the health care cost of dementia in the United States will total $259 billion. People with the disease will also incur about $10,000 in out-of-pocket expenses for the year. Annual deaths from Alzheimer’s nearly doubled between 2000 and 2014, while deaths from other major killers, such as heart disease, stroke, prostate cancer, and HIV, fell.—Madolyn Bowman Rogers

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  1. This very interesting paper illustrates the value of national general practitioner databases, as available in the Netherlands, and the caveats in replacing carefully collected epidemiological data with data abstracted from medical records. In the latter, changes in practice habits can affect the results. As the authors point out, the “increase” in incidence, most prominent above age 85 and seen to a small extent in those over 75, is likely a combination of increased life expectancy (mean age likely increasing even within the five-year age categories), earlier dementia diagnosis, and a greater proportion of persons with early dementia living in the community with support (hence registered with GPs, whereas nursing home residents are not).

    We all agree that the trends in dementia need to be studied in more populations and explanations sought for the findings. That could aid our efforts at primary prevention/delay of clinical dementia.

  2. A newly published paper by Yi Zeng and colleagues reported increasing cognitive impairment among oldest-old in China based on data from the Chinese Longitudinal Healthy Longevity Study (CLHLS) 1998 and 2008 surveys. The findings are relevant to the Netherlands study, even though it is obvious that huge differences exist between the two countries (Zeng et al., 2017).

    Yi and coauthors used the "costs of success" theory to explain their findings: Lifespan extension might expand disability of cognitive functioning as more frail, elderly individuals survive with health problems. The same principle may at least partially apply to the findings from the Dutch population.

    I and coworkers are working on the CLHLS cognitive data collected from the 2002, 2005, 2008, 2010, and 2014 surveys. The results on time trend are highly interesting. I expect to finalize and publish the finding in the near future and hope the results will offer fresh evidence on the temporal trends of cognitive health.

    For increased awareness and help-seeking behaviors, and changes in diagnosing practice, it would be helpful if information on dementia severity can be obtained and analyzed on at least a subsample of the study population. I would expect to see an increasing proportion of mild (early) dementia cases among all diagnosed cases.

    References:

    . Survival, disabilities in activities of daily living, and physical and cognitive functioning among the oldest-old in China: a cohort study. Lancet. 2017 Apr 22;389(10079):1619-1629. Epub 2017 Mar 10 PubMed.

  3. This appears to be the first study suggesting that the incidence of dementia may have increased, rather than decreased, in recent decades. The study was based on all data on dementia diagnosis from general practitioner networks in the Netherlands between 1992 and 2014. Over 23 years of study, the authors observed more than 23,000 incident dementia cases in 4 million person-years at risk.

    It remains unclear whether the findings contradict previous studies, or whether the increase in incidence is spurious and caused by increased awareness of dementia in the general population and among general practitioners. As clearly recognized by the authors, the increasing trend may represent a balance between increasing detection and stable risk or, more extremely, between increasing detection and a true decreasing risk. In this last scenario, the increased detection would have completely masked a genuine decline in incidence.

    There are three important messages to note:

    1.   The time trends for dementia are complex, and more data are needed to clarify what is happening.

    2.   The future of dementia remains somewhat unclear. Even if the incidence has declined and continues to decline, the prevalence may remain the same or increase if survival of persons affected by dementia increases. In addition, even if the prevalence declines, the total number of persons affected by dementia may remain the same or increase if the size of the elderly population expands.

    3.   We cannot be sure that the decline in incidence will continue in the coming decades. With cautious optimism, we may conclude that the burden of dementia may be modified over time by human practices, including public health and medicine.

    References:

    . Time, Sex, Gender, History, and Dementia. Alzheimer Dis Assoc Disord. 2017 Jan-Mar;31(1):76-79. PubMed.

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References

News Citations

  1. Falling Dementia Rates in U.S. and Europe Sharpen Focus on Lifestyle
  2. U.S. Dementia Rates Fall
  3. Dementia Prevalence Falls in England
  4. Falling Dementia Rates in U.S., Europe Hint at Prevention Benefit
  5. Dementia Incidence in Britain Dropped, Mostly in Men
  6. Prevalence of Dementia, AD, in China Eclipses Predictions
  7. World Alzheimer Report 2015: Revised Estimates Hint at Larger Epidemic
  8. Global Rise in Total AD Cases Dwarfs Falling Age-Standardized Rate

Further Reading

Primary Papers

  1. . Dementia incidence trend over 1992-2014 in the Netherlands: Analysis of primary care data. PLoS Med. 2017 Mar;14(3):e1002235. Epub 2017 Mar 7 PubMed.
  2. . What's the "Take Home" from Research on Dementia Trends?. PLoS Med. 2017 Mar;14(3):e1002236. Epub 2017 Mar 7 PubMed.