AbstractBackgroundMild cognitive impairment (MCI) is a diagnostic entity associated with increased risk of incident dementia. Prior epidemiological studies have associated illiteracy and low to no formal education with increased prevalence of MCI and dementia. A recent study using a robust neuropsychological approach with the harmonized cognitive assessment ancillary study (Mex‐Cog) of the Mexican Health and Aging Study (MHAS) found that low education as well as older age, depression, diabetes, and rurality were independently associated with MCI among older adults. Rates of illiteracy are relatively high among older adults in Mexico, due to limited access to formal education, but some people attained literacy despite not attending school. To assess the unique contribution of literacy to MCI independent of educational achievement in a Mexican population, we evaluated literate and illiterate older adults with no formal schooling.MethodAnalyses included a sample of literate and illiterate non‐demented adults over the age of 55 living in both urban and rural areas of Mexico who reported that they never attended school (N = 231). MCI diagnosis was assigned based on a comprehensive cognitive assessment for domains of memory, executive functioning, language, and visuospatial ability. Cognitive impairment was defined using a robust norms approach and a 1.5‐SD cut‐off per cognitive domain correcting for age, years of education, and sex. Multinomial logistic regressions evaluated the association of self‐reported literacy, age, and sex with risk of MCI. We then evaluated whether the relationship between literacy and MCI remained after controlling for sociodemographic and health factors.ResultIlliteracy was associated with increased risk of MCI (OR=6.05 [3.33, 11.34]) compared to literate participants. The relationship between literacy and risk of MCI persisted after taking into account depression, rurality, hypertension, and diabetes.ConclusionWe found that illiteracy was independently associated with higher risk of prevalent MCI. Our findings suggest that independent of formal education, attainment of literacy has a long‐lasting impact on brain health at older ages. Future studies in low socioeconomic populations should consider functional literacy as a powerful predictor of cognitive function in old age.