Table 4.
Main results of four prospective studies of smoking and dementia
| Study | Contrast in smoking habits | Follow up duration (years) | Alzheimer's disease
|
Any dementia
|
|||
|---|---|---|---|---|---|---|---|
| No of cases | Risk ratio (95% CI) | No of cases | Risk ratio (95% CI) | ||||
| Short term studies of incident disease on reinterview | |||||||
| Wang et al18 (both sexes, aged ⩾75) | Ever* v never | 3 | 34 | 1.1 (0.5 to 2.4) | 46 | 1.4 (0.8 to 2.7) | |
| Hebert et al17 (both sexes, aged ⩾65) | Ever v never | 3 | 76 | 0.7 (0.3 to 1.4) | — | — | |
| Launer et al6 (both sexes, aged ⩾65) | Current v never | 2 | 277 | 1.74 (1.21 to 2.50) | 400 | 1.39 (1.03 to 1.89) | |
| Long term study of dementia on death certificate | |||||||
| Doll et al (male UK doctors) | Current v not† | 47 | 370 | 0.99 (0.78 to 1.25) | 473 | 0.96 (0.78 to 1.18) | |
*
Excludes those who had smoked less than five cigarettes per day and stopped several decades ago.
†
Smoking status as last determined at least 10 years (mean 15 years) before death: our current smokers were at that time still continuing to smoke. Our ex-smokers stopped a mean of 34 years before death, so comparison group includes them: inclusion of ex-smokers in the Launer et al comparison group would change their risk ratios into 1.64 (1.16 to 2.31) for Alzheimer's disease and 1.38 (1.03 to 1.84) for any dementia.