Dementia Incidence in Britain Dropped, Mostly in Men

Evidence continues to mount that fewer people are developing dementia now than in past decades. The latest study to report this appeared in the April 19 Nature Communications. Researchers led by Carol Brayne at the University of Cambridge, England, directly compared incidence in representative population samples in multiple geographic areas of the United Kingdom in the early 1990s with that during 2008-2011. They found a lower rate in the recent cohort, which resulted in an estimated 20 percent fewer new dementia cases at the population level than would have been expected based on the older rates. Intriguingly, this drop was driven mostly by fewer new cases among men. This contrasts with some other recent studies where researchers reported greater drops in incidence among women. The discrepancy suggests different factors may be at work in different populations, researchers noted. Meanwhile, the overall findings bolster the evidence for declining dementia rates in the Western world.

Might dementia incidence be falling in men over 80?

Researchers said the data should fuel a push toward prevention. “We need to change our thinking to focus, with a sense of optimism, on strategies to delay dementia onset. We’re already making progress—we just didn’t know it until fairly recently,” Eric Larson at Group Health Research Institute, Seattle, wrote to Alzforum. Kristine Yaffe at the University of California, San Francisco, expressed enthusiasm as well. “These results are really exciting. They tell us that public health interventions are having a big effect on brain health.”

Multiple studies from the United States and Europe have now reported declining dementia incidence, although in many cases this was inferred from prevalence data, and in other cases the trend did not reach statistical significance in small, geographically limited, short-term studies (see May 2013 news). Recently, researchers led by Sudha Seshadri at Boston University measured a roughly 20 percent drop in new dementia cases per decade from the late 1970s to the early 2010s in the Framingham Heart Study cohort, firming up the evidence that incidence is truly on the wane in developed countries (see Feb 2016 news). 

The U.K. study took a different approach to calculating incidence. Rather than follow a single cohort over time, it measured incidence among two similar cohorts 20 years apart. In the early 1990s the researchers recruited a representative population sample of more than 7,000 people aged 65 and older from five regions in the United Kingdom, in what was called the first Cognitive Function and Ageing Study (CFAS I). They calculated AD prevalence data from this sample, then followed up with a subset of the cognitively healthy participants two years later to determine how many of them had developed dementia, as measured by scores on the Geriatric Mental State exam. Twenty years later, the authors recruited a similarly sized, independent population sample from three of the same geographic areas for CFAS II. They used identical assessment methods and follow-up to enable direct comparison between the cohorts.

In 2013, the authors reported that they were surprised to find nearly identical dementia prevalence estimates in CFAS I and II despite the overall aging of the population over those two decades (see Jul 2013 conference news). This suggested that incidence might have dropped. Now, the authors confirm this hunch with the actual incidence numbers. The number of new cases fell from 20 per 1,000 person-years in CFAS I to 17.7 in CFAS II. This had a notable effect. When adjusted for the aging of the population, the incidence rate seen in CFAS I would have resulted in an estimated 251,000 new cases of dementia in the United Kingdom in 2010. However, the actual number of new cases based on CFAS II rates was about 210,000, a drop of around 20 percent. The reported decline is similar, although slightly smaller, to that seen in other recent studies, which estimated incidence drops of 20-30 percent per decade. “The fact that we’re getting similar signals from different [study] designs is very compelling,” Brayne said.

When the authors broke down the decline by age and gender, they found that incidence tapered off only slightly in women. Most of the drop came from men, particularly those over age 80, making their CFAS II incidence rates lower than in women of the same age. At younger ages, incidence rates were higher in men in CFAS I, but about equal in both sexes in CFAS II. The drop in men’s rates contrasts with the Framingham findings and a recent study from Germany, where women’s numbers drove the downward incidence trend. However, the new British data match findings from Sweden and Southern Europe, where men benefited the most (see Qiu et al., 2013; Lobo et al., 2007). 

Researchers don’t know the reason for the gender discrepancies, but suggested there could be several factors at work. “There may be major differences in lifestyle, health, and exposure to different risks across genders and countries,” Brayne told Alzforum. Lower incidence in men in particular might be due to better cardiovascular care, suggested Yaffe. She noted that men were disproportionately affected by cardiovascular disease in the past, and have benefited more than women from statin therapies. “There are interesting gender differences around cardiovascular disease and risk-factor management,” Yaffe said. Conversely, women may have benefited more than men from increased educational opportunities in recent decades, and this might explain better outcomes in women in some populations, she speculated.

The findings also highlight the importance of experiences throughout life in determining brain health in old age, the researchers stressed. Dementia risk may begin early in life, Yaffe noted. “The brain responds to lifelong exposure to risk factors,” she told Alzforum. Brayne agreed, “These studies tell us we should pay more attention to factors in society that facilitate the health of the brain and the body through the whole life course.”—Madolyn Bowman Rogers

Comments

  1. 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 Larson

  2. 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. 

    References:

    Gao S, Ogunniyi A, Hall KS, Baiyewu O, Unverzagt FW, Lane KA, Murrell JR, Gureje O, Hake AM, Hendrie HC. Dementia incidence declined in African-Americans but not in Yoruba. Alzheimers Dement. 2015 Jul 26; PubMed.

    Grasset L, Brayne C, Joly P, Jacqmin-Gadda H, Peres K, Foubert-Samier A, Dartigues JF, Helmer C. Trends in dementia incidence: Evolution over a 10-year period in France. Alzheimers Dement. 2016 Mar;12(3):272-80. Epub 2015 Dec 13 PubMed.

    Jagger C, Matthews FE, Wohland P, Fouweather T, Stephan BC, Robinson L, Arthur A, Brayne C, Medical Research Council Cognitive Function and Ageing Collaboration. A comparison of health expectancies over two decades in England: results of the Cognitive Function and Ageing Study I and II. Lancet. 2016 Feb 20;387(10020):779-86. Epub 2015 Dec 9 PubMed.

    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.

    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.

    Qiu C, Fratiglioni L. A major role for cardiovascular burden in age-related cognitive decline. Nat Rev Cardiol. 2015 May;12(5):267-77. Epub 2015 Jan 13 PubMed.

    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.

    Satizabal CL, Beiser AS, Chouraki V, Chêne G, Dufouil C, Seshadri S. Incidence of Dementia over Three Decades in the Framingham Heart Study. N Engl J Med. 2016 Feb 11;374(6):523-32. PubMed.

    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.

    Sposato LA, Kapral MK, Fang J, Gill SS, Hackam DG, Cipriano LE, Hachinski V. Declining Incidence of Stroke and Dementia: Coincidence or Prevention Opportunity?. JAMA Neurol. 2015 Dec;72(12):1529-31. PubMed.

    Wiberg P, Waern M, Billstedt E, Ostling S, Skoog I. Secular trends in the prevalence of dementia and depression in Swedish septuagenarians 1976-2006. Psychol Med. 2013 Dec;43(12):2627-34. Epub 2013 Mar 12 PubMed.

    Wimo A, Sjölund BM, Sköldunger A, Qiu C, Klarin I, Nordberg G, von Strauss E. Cohort Effects in the Prevalence and Survival of People with Dementia in a Rural Area in Northern Sweden. J Alzheimers Dis. 2015;50(2):387-96. PubMed.

    Winblad B, Amouyel P, Andrieu S, Ballard C, Brayne C, Brodaty H, Cedazo-Minguez A, Dubois B, Edvardsson D, Feldman H, Fratiglioni L, Frisoni GB, Gauthier S, Georges J, Graff C, Iqbal K, Jessen F, Johansson G, Jönsson L, Kivipelto M, Knapp M, Mangialasche F, Melis R, Nordberg A, Rikkert MO, Qiu C, Sakmar TP, Scheltens P, Schneider LS, Sperling R, Tjernberg LO, Waldemar G, Wimo A, Zetterberg H. Defeating Alzheimer's disease and other dementias: a priority for European science and society. Lancet Neurol. 2016 Apr;15(5):455-532. PubMed.

    Wu YT, Fratiglioni L, Matthews FE, Lobo A, Breteler MM, Skoog I, Brayne C. Dementia in western Europe: epidemiological evidence and implications for policy making. Lancet Neurol. 2016 Jan;15(1):116-24. Epub 2015 Aug 21 PubMed.

    View all comments by Chengxuan Qiu

  3. 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. Rocca

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References

News Citations

  1. Dementia Incidence Said to Drop as Public Health Improves
  2. Falling Dementia Rates in U.S. and Europe Sharpen Focus on Lifestyle
  3. Dementia Prevalence Falls in England

Paper Citations

  1. 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.
  2. Lobo A, Saz P, Marcos G, Dia JL, De-la-Camara C, Ventura T, Montañes JA, Lobo-Escolar A, Aznar S, . Prevalence of dementia in a southern European population in two different time periods: the ZARADEMP Project. Acta Psychiatr Scand. 2007 Oct;116(4):299-307. PubMed.

Further Reading

Primary Papers

  1. 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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