The study has three interventions; i) folate and vitamin B12, ii) physical activity; and iii) mental health literacy. Participants will be randomly allocated to receive each combination of the interventions (folate and vitamin B12 or placebo, physical activity intervention programme or physical activity no-intervention control, mental health literacy intervention [containing written modules with information about depression that is relevant to older people] or mental health literacy no-intervention control group). Participants will receive these interventions over a two-year period with regular assessments across that time period.