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Table 2 Studies estimating changes in the incidence of dementia or Alzheimer’s disease over time

From: Recent global trends in the prevalence and incidence of dementia, and survival with dementia

Study, setting, age range Outcomes Relative change (%) Period Interval between incidence cohorts (years) Relative change (%) per year Other findings
Directly observed
 1. Indianapolis, IN, USA, African Americans, 65 years and older [36] Dementia (DSM-III-R)
AD
Dementia
3.6 % per annum (3.2–4.1 %) vs. 1.4 % per annum (1.2–1.7 %)
61 % reduction
AD
2.5 % per annum (2.1–2.9 %) vs. 1.3 % per annum (1.0–1.5 %)
48 % reduction
1991–2002 11 years Dementia
−5.5 %
AD
−4.4 %
Biggest reduction in youngest age groups.
See also notes for study 4 in Table 1.
 2. Framingham, MA, USA, 60 years and older [37] Dementia DSM-IV
AD (NINCDS-ADRDA)
VaD (NINDS-AIREN); diagnoses by consensus review panel
Dementia
44 % reduction
AHR 0.56 (0.41–0.77)
AD
30 % reduction
AHR 0.70 (0.48–1.03)
VaD
55 % reduction
AHR 0.45 (0.23–0.87)
1980–2006 26 years Dementia
−1.7 %
AD
−1.2 %
VaD
−2.1 %
Biggest reduction in youngest age groups.
No reduction among the least educated.
Significant improvements in education status; use of antihypertensive and statin medication; blood pressure and HDL levels; and prevalence of smoking, heart disease and stroke; however, prevalence of obesity and diabetes increased.
 3. Bordeaux, France, 65 years and older [38] Algorithm diagnosis (using MMSE score and IADL only)
Clinical diagnosis ‘based upon’ DSM-IIIR/DSM-V
Algorithmic diagnosis
Overall AHR 0.65 (0.53–0.81)
Women AHR 0.62 (0.48–0.80)
Men AHR 1.10 (0.69–1.78)
Clinical diagnosis
Overall 0.92 (0.73–1.15)
Women 0.90 (0.69–1.17)
Men 1.21 (0.76–1.93).
1988/1989–1998/1999 and 1999/2001– 2009/2010 10 years Overall
−3.5 %
Women
−3.8 %
Compared with the earlier cohort, the later cohort had more education, a higher BMI, a lower prevalence of stroke, and were less likely to be a current and more likely to be former smokers. More use of antihypertensive and lipid-lowering drugs. At baseline, they were less disabled on the 4-item IADL score and had higher MMSE scores.
Differences in education, vascular factors and depression accounted only to some extent for this reduction (overall AHR 0.77, 95 % CI 0.61–0.97; women AHR 0.73, 95 % CI 0.57–0.95).
 4. Rotterdam, the Netherlands, 60–90 years [39] Dementia (DSM-III-R) Non-significant 25 % reduction
RR 0.75 (0.56–1.02)
1990–2000 10 years −2.5 % Hypertension, diabetes and obesity increased. Higher education. More diabetes treatment, more anti-thrombotics and much more statins. More past but less current smoking. Substantial reduction in overall mortality: HR 0.63 (0.52–0.77).
 5. Germany, insurance claims data, 65 years and older [40] Dementia (ICD-10), or using cholinesterase inhibitors or memantine 9 % reduction
Men 0.91 (0.85–0.97)
Women 0.91 (0.87–0.95)
2004–2007/2007–2010 3 years −3.0 % This study used claims data of the largest public health insurance company in Germany. The data contained complete inpatient and outpatient diagnoses according to ICD-10 codes. For the analysis of incidence, two independent age-stratified samples were taken, the first comprising 139,617 persons in 2004 with follow-up until 2007, the second with 134,653 persons in 2007 with follow-up until 2010. Secular trends in clinical diagnosis or help-seeking cannot be excluded.
 6. Ontario, Canada; health insurance plan, hospital discharge and ambulatory care register; age range not reported [41] Dementia diagnosis (ICD-9 or ICD-10) or cholinesterase inhibitor prescription 7.4 % reduction; statistical significance of trend not reported 2002–2013 12 years −0.6 % This study used claims data of the single state-provided insurance plan and comprehensive hospital admission, ambulatory care and drug prescription databases. Annual incidence rates, age- and sex-standardised, are reported for each year between 2002 and 2013. The trend is not linear, and statistical significance is not reported. Secular trends in clinical diagnosis or help-seeking cannot be excluded.
 7. Chicago, IL, USA [31] AD Stable
OR 0.97 (0.90–1.04)
1997–2008 11 years No trend  
 8. Ibadan, Nigeria [52] Dementia (DSM-III-R)
AD
Stable
Dementia
1.7 % per annum (1.4–2.0 %) vs. 1.4 % per annum (1.1–1.6 %)
AD
1.5 % per annum (1.2–1.8 %) vs. 1.0 % (0.7–1.2 %)
1991–2002 11 years No trend  
Inferred
 9. Stockholm, Sweden, 75 years and older [29] Dementia (DSM-III-R) Reduced incidence inferred from stable prevalence but increased survival with dementia 1988–2002 14 years Not reported See also notes for Table 1, study 5.
  1. AD Alzheimer’s disease, AHR adjusted hazard ratio, BMI body mass index, DSM Diagnostic and Statistical Manual of Mental Disorders, HDL high-density lipoprotein, IADL instrumental activities of daily living, ICD International Classification of Diseases, MMSE Mini Mental State Examination, NINCDS-ADRDA National Institute of Neurological and Communicative Disorders and Stroke and the Alzheimer’s Disease and Related Disorders Association, NINDS-AIREN National Institute of Neurological Disorders and Stroke and Association Internationale pour la Recherche et l’Enseignement en Neurosciences, RR relative risk, VaD vascular dementia