van Bussel EF, Richard E, Arts DL, Nooyens AC, Coloma PM, de Waal MW, van den Akker M, Biermans MC, Nielen MM, van Boven K, Smeets H, Matthews FE, Brayne C, Busschers WB, van Gool WA, Moll van Charante EP. 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.

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Comments

  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.

    View all comments by Sudha Seshadri

  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:

    Zeng Y, Feng Q, Hesketh T, Christensen K, Vaupel JW. 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.

    View all comments by Lei Feng

  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:

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

    View all comments by Walter A. Rocca

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