Promoting good cognitive functioning and preventing dementia in late life are priority actions for many countries with rapidly ageing populations. Although epidemiological research has established some modifiable factors that influence the risk of cognitive impairment (such as low education level, hearing impairment, smoking, obesity, physical inactivity or social isolation), a growing literature suggests further risk and protective factors that might affect cognitive functioning and dementia. In this Review, we examine the potential effects of these less well-established factors, and discuss promotion and prevention strategies at the population and individual levels that might reduce dementia risk in the long term. Reducing financial struggles, neighbourhood deprivation and workplace strain and promoting leisure activities, emotional wellbeing and healthy nutritional styles have emerged as factors that might help to prevent dementia and could be included among priority actions for healthy cognitive ageing.