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

 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

 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.