Education and the moderating roles of age, sex, ethnicity and apolipoprotein epsilon 4 on the risk of cognitive impairment

•We examined the association between education and cognitive impairment (CI).•Moderating influences of age, sex, ethnicity, and APOE*4 carriage were tested.•Higher education was related to lower CI risk, but this effect weakened with age.•The effect of education on lower CI risk was stronger in women than men.•High School education lowered CI risk in Blacks and Asians, but not Whites. We examined how the relationship between education and latelife cognitive impairment (defined as a Mini Mental State Examination score below 24) is influenced by age, sex, ethnicity, and Apolipoprotein E epsilon 4 (APOE*4). Participants were 30,785 dementia-free individuals aged 55–103 years, from 18 longitudinal cohort studies, with an average follow-up ranging between 2 and 10 years. Pooled hazard ratios were obtained from multilevel parametric survival analyses predicting cognitive impairment (CI) from education and its interactions with baseline age, sex, APOE*4 and ethnicity. In separate models, education was treated as continuous (years) and categorical, with participants assigned to one of four education completion levels: Incomplete Elementary; Elementary; Middle; and High School. Compared to Elementary, Middle (HR = 0.645, P = 0.004) and High School (HR = 0.472, P