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Matthews FE, Stephan BC, Robinson L, Jagger C, Barnes LE, Arthur A, Brayne C, Cognitive Function and Ageing Studies (CFAS) Collaboration. A two decade dementia incidence comparison from the Cognitive Function and Ageing Studies I and II. Nat Commun. 2016 Apr 19;7:11398. PubMed.
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This recent publication from the CFAS project in the U.K. is important. It shows clearly that incidence rates for dementia have decreased about 20 percent over the two decades between CFAS 1 and CFAS II. Incidence rates are a better way to make comparisons over time because they are less effected by differential mortality. They indicate that in the U.K., the number of new cases each year is not much greater even though the population of older persons has increased dramatically. More importantly, though, is that the rates indicate that late-life dementia risk and brain aging in general is affected by changes that occur through the life course. Better educational levels and socioeconomic conditions, better treatments of vascular risk, and better health habits in general can have a favorable effect on events years later. As the authors note, “Primary prevention of dementia as opposed to secondary (early detection) or tertiary (mitigation once present) through healthier life course at societal levels, reduced vascular risk, and enhanced opportunity for all types of engagement is likely to be more cost effective than national initiatives, such as dementia strategies targeted at earlier and earlier identification of at–risk states.”
It is also an encouraging message in that it confirms what many studies have now indicated—rates are declining even if absolute numbers are increasing—and that means that we need to change our thinking to focus on strategies to delay dementia onset, with a sense of optimism. We’re already making progress—we just didn’t know this until fairly recently.
View all comments by Eric LarsonKarolinska Institutet
Declining incidence suggests that dementia might be preventable or postponable
Dementia is a major cause of disability, institutionalization, and poor quality of life in old age and significantly increases the monetary costs to individuals, families, and societies (Winblad et al. 2016). In 2015, Alzheimer’s Disease International (WHO/ADI) estimated that, worldwide, the number of people living with dementia had reached ~48 million, and projected that number would double approximately every 20 years, driven primarily by population aging (The World Alzheimer Report 2015, The Global Impact of Dementia: An analysis of prevalence, incidence, cost and trends. ADI, 2015). The estimated global cost of dementia care (~$604 billion) accounted for ~1 percent of global gross domestic product. Thus, dementia has been identified as a global public health priority by the World Health Organization (WHO) and the London G8 Dementia Summit (Dementia: a public health priority: WHO, Geneva, 2012; Policy Brief for G8 Heads of Government. The Global Impact of Dementia 2013-2050. London: ADI, 2013).
In the last decade, several reports have shown a stable or declining age-specific prevalence of dementia in North America and Europe starting from the 1980s (Langa et al., 2008; Qiu et al., 2013; Matthews et al., 2013; Wu et al., 2016), although a difference has been reported in Asian countries (e.g., Japan, Hong Kong and Mainland China) (Winblad et al., 2016). Most recently, several well-designed studies from North America, including the Framingham Heart Study, consistently show that incidence of dementia has been declining since as early as the late 1970s (Sposato et al., 2016; Satizabal et al., 2016; Gao et al., 2016). Similarly, there is suggestive, but not conclusive, evidence that incidence of dementia might have declined in Europe since the late 1980s (Schrijvers et al., 2012; Qiu et al., 2013; Wiberg et al., 2013; Grasset et al., 2016). This U.K. Cognitive Function and Ageing Study (CFAS) by Matthews and colleagues has now added additional evidence supporting the declining incidence of dementia in Europe during the past two to three decades.
Data from CFAS have previously shown a decreased prevalence of dementia over two decades (Matthews et al., 2013). In support of the previous study, the latest CFAS data provide evidence for a decline in incidence of dementia in the U.K., especially in men. Rather stable methods (e.g., sampling and diagnostic methods) have been applied in CFAS over time, although it is not entirely clear to what extent the slight differences in identifying prevalent cases of dementia at baseline as well as in ascertaining incident cases of dementia at two-year follow-ups between the two time periods (CFAS I and CFAS II) might contribute to the marginal decline of incidence of dementia.
A decline in incidence of dementia over time implies that dementia might be preventable, or at least its onset postponable, by interventions targeting modifiable risk and protective factors. In this regard, it is important to understand risk and compensatory factors as well as mechanisms that lead to the declining incidence. It has been suggested that the decline in occurrence of dementia might be due to compression of cognitive disorders in aging (Langa et al., 2008; Jagger et al., 2016). From a public health perspective, it is highly relevant to further investigate the potential modifiable factors that contribute to the declining trends of dementia prevalence and incidence. For instance, it has been well established that cardiovascular risk factors play a major role in cognitive decline and dementia (Qiu and Fratiglioni, 2015), and that the risk of cardiovascular events in Western Europe and North America has steadily decreased since the 1970s-1980s (Sposato et al., 2015; Wu et al., 2016; Winblad et al., 2016). However, it remains to be clarified whether, and to what extent, the decline in dementia incidence is attributed to improvement in cardiovascular health over time. In addition, the contributions of psychosocial factors, such as increased educational attainments and leisure activities over time, to the trends of dementia occurrence also deserve exploration. It has been hypothesized that these psychosocial factors could increase cognitive reserve, thus postponing the onset of the dementia syndrome (Winblad et al., 2016). This has significant implications for achieving a longer and healthier life given that there is currently no cure for dementia.
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View all comments by Chengxuan QiuMayo Clinic
The study is methodologically sound, the analyses quite sophisticated, and the manuscript well written. The discussion addresses some important political issues (see below).
The important discovery from this study, and from previous studies of incidence in Western countries, is that the risk of dementia (incidence rate) is changing in entire populations (large-scale trends). This is very important because it confirms the possibility of primary prevention. Interventions to improve health and well-being at the population level starting during intrauterine life, and continuing throughout childhood, adolescence, and mature life, may change the aging processes in general, and brain aging in particular.
The falling dementia incidence in the United Kingdom was driven by a drop in men rather than women. Interestingly, the incidence was higher in men than women in the initial study (around 1990), contrary to other European studies suggesting that the incidence is higher in women. I have two comments on this: 1) The men-to-women differences may vary across countries (e.g., United Kingdom versus Sweden) and across historical periods (e.g., a study in 1990 versus a study in 2010); 2) The declining trends of dementia for men and women may vary across countries and across time periods because of the interaction of sex and gender factors with a changing environmental, social, and cultural setting (e.g., interaction of sex and gender with “living conditions” as represented in this paper by the concept of “deprivation”). As a result, the decline in incidence may be greater in women in one setting (e.g., Germany and United States data) and in men in another setting (e.g., United Kingdom and Spain).
Overall, there may be an important dynamic interaction between sex, gender, and deprivation over historical epochs of the last century. For example, the people involved in this study have lived through Word War II and periods of food restriction, infectious epidemics, political unrest, natural catastrophes, introduction of mass media (e.g., widespread use of radios and televisions), changes in the physical environment (e.g., increased use of herbicides and pesticides), and changes in medical care (e.g., introduction of antibiotics and anti-hypertensive drugs). These dramatic changes are likely to impact women differently from men. For example, men went to war in 1940-1945, whereas women stayed home with the elderly and children.
This study reminds us that investing some of our societal money in primary prevention may be more prudent than putting all of our resources in the search for a magic treatment for Alzheimer’s disease or for expensive and invasive biomarkers to predict the future occurrence of disease.
View all comments by Walter A. RoccaMake a Comment
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