Cigarette smoking had highly variable associations with incident Alzheimer disease (RR 0.27-2.72) and dementia (RR 0.38-1.42), with heterogeneity largely explained by minimum age at entry.
Systematic Review
Does cigarette smoking affect the incidence of Alzheimer disease and dementia compared to nonsmokers?
The association between smoking and dementia or Alzheimer's disease is highly heterogeneous across studies, which may be largely explained by selection bias due to censoring by death at older ages.
Effect estimate: RR 0.27 to 2.72 (Alzheimer disease); RR 0.38 to 1.42 (dementia)
We conducted a systematic review of published prospective studies that estimated the association between smoking and the incidence of Alzheimer disease and dementia. The relative rate for smokers versus nonsmokers ranged from 0.27 to 2.72 for Alzheimer disease (12 studies) and from 0.38 to 1.42 for dementia (6 studies). The minimum age at entry (range: 55-75 years) explained much of the between-study heterogeneity in relative rates. We conjecture that selection bias due to censoring by death may be the main explanation for the reversal of the relative rate with increasing age.
Hernán et al. (Thu,) conducted a systematic review in Alzheimer disease and dementia. Cigarette smoking vs. Nonsmokers was evaluated on Incidence of Alzheimer disease and dementia (RR 0.27 to 2.72 (Alzheimer disease); RR 0.38 to 1.42 (dementia)). Cigarette smoking had highly variable associations with incident Alzheimer disease (RR 0.27-2.72) and dementia (RR 0.38-1.42), with heterogeneity largely explained by minimum age at entry.