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