Table 4.
Temporal Trends in the Incidence of Dementia, Adjusted for Educational Level, Vascular Risk Factors at Midlife, and Cardiovascular Disease.*
| Variable | No. of Cases of Dementia |
Total No. of Observation Periods |
5-Yr Hazard Ratio (95% CI)† |
P Value for Trend |
|||
|---|---|---|---|---|---|---|---|
| Epoch 2 | Epoch 3 | Epoch 4 | Trend‡ | ||||
| High school diploma | 358 | 8778 | 0.82 (0.61–1.10) |
0.68 (0.50–0.91) |
0.65 (0.47–0.91) |
0.85 (0.75–0.95) |
0.005 |
| Increase in systolic blood pressure at midlife |
361 | 8837 | 0.76 (0.56–1.01) |
0.61 (0.46–0.81) |
0.54 (0.40–0.75) |
0.79 (0.71–0.89) |
<0.001 |
| Increase in body-mass index at midlife |
352 | 8658 | 0.78 (0.59–1.05) |
0.62 (0.47–0.83) |
0.56 (0.41–0.76) |
0.80 (0.71–0.89) |
<0.001 |
| Type 2 diabetes at midlife | 284 | 7418 | 0.76 (0.55–1.06) |
0.55 (0.39–0.76) |
0.50 (0.35–0.71) |
0.76 (0.67–0.86) |
<0.001 |
| Preexisting and incident stroke | 371 | 9015 | 0.78 (0.59–1.04) |
0.62 (0.47–0.82) |
0.58 (0.42–0.78) |
0.81 (0.72–0.90) |
<0.001 |
| Preexisting cardiovascular disease | 371 | 9015 | 0.78 (0.59–1.04) |
0.62 (0.47–0.82) |
0.57 (0.41–0.77) |
0.80 (0.72–0.90) |
<0.001 |
| Preexisting atrial fibrillation | 371 | 9015 | 0.78 (0.59–1.04) |
0.61 (0.46–0.81) |
0.55 (0.40–0.75) |
0.79 (0.71–0.89) |
<0.001 |
The baseline examination period was between 1977 and 1983 for the first epoch, between 1986 and 1991 for the second epoch, between 1992 and 1998 for the third epoch, and between 2004 and 2008 for the fourth epoch.
The hazard ratios in each row are adjusted for the variable shown in the first column of that row. In addition, the 5-year hazard ratios (the incidence of dementia during each epoch relative to the incidence during the first epoch) are adjusted for age and sex.
We estimated linear trends (the decline per decade in the 5-year incidence of dementia) using the elapsed mean time (in decades) between the first epoch and each consecutive epoch.