In the seminal report of the Lancet Commission on dementia [54] the identification of contributory risk factors, their effect size and their modifiabilty, led to a startling conclusion: as much as 40% of dementia could be prevented by immediate application of known interventions. Not by a novel disease-modifying treatment but a systematic approach to resolve and reduce risk factors across the lifespan. Early-life education; mid-life obesity, hypertension and hearing loss; and later life exercise, smoking, social isolation, diabetes, depression and pollution contribute to this potential for dementia prevention.