The adverse effect of modifiable dementia risk factors on cognition amplifies across the adult lifespan

BACKGROUND: Reversible lifestyle behaviors (modifiable risk factors) can reduce dementia risk by 40%, but their prevalence and association with cognition throughout the adult lifespan is less well understood. METHODS: The associations between the number of modifiable risk factors for dementia (low education, hypertension, hearing loss, traumatic brain injury, alcohol or substance abuse, diabetes, smoking, and depression) and cognition were examined in an online sample (N = 22,117, ages 18–89). FINDINGS: Older adults (ages 66–89) had more risk factors than middle‐aged (ages 45–65) and younger adults (ages 18–44). Polynomial regression revealed that each additional risk factor was associated with lower cognitive performance (equivalent to 3 years of aging), with a larger association as age increased. People with no risk factors in their forties to seventies showed similar cognitive performance to people 10 or 20 years younger with many risk factors. INTERPRETATION: Modifiable dementia risk factors amplify lifespan age differences in cognitive performance.