Background Cognitive decline represents a major public health impact on individuals and governments around the world. There is a well-established relationship between specific lifestyle behaviours and cognitive decline, but extremely limited research on the role of combined behaviours. The aim of these analyses was to examine the role of lifestyle behaviours (smoking, physical activity and dietary choice) separately and in combination on 20-year cognitive decline from from age 43 years to 60–64 (60+) years in a prospective longitudinal population-based study.

Methods Participants were 1018 study members from the UK MRC National Survey of Health and Development regularly followed up since birth in 1946. Cognitive functioning was measured at age 43 years and 60+ years using tests of verbal memory (maximum words recalled 45) and timed visual search (maximum letter searched 600). Lifestyle behaviours were examined at 36 & 43 years and overall early-midlife scores were calculated. Smoking was classified as non-smoker, moderate or heavy smoker (20+ cigarettes per day). Physical activity was classified as inactive, moderate or mostly active (> 5+ activities/month). Dietary choice was classified as high/low quality diet based on breakfast consumption, type of milk & bread, daily portions of fruit and vegetables and energy derived from fat. The covariates included in these analyses were social class of origin, childhood cognition, education, adult social class and depression.

Results Key findings were that high quality dietary choices made in early-midlife were associated with slower memory decline β = 0.64 (95% CI 0.05 to 1.24) as compared to low quality dietary choices, and most active levels of physical activity were associated with a slower visual search speed decline β = 13.45 (2.43 to 24.47) compared to those who were inactive. Heavy smoking was marginally associated with faster decline in visual search speed compared to non-smokers, but not with memory decline. These associations were independent from each other in terms of lifestyle behaviours as well as from the selected covariates.

Conclusion The current results suggest that physical activity and healthy dietary choice are protective of cognitive decline, and that smoking is harmful in this respect. Public health interventions based on modifiable lifestyle behaviours across the life course represent high level priorities and should be regarded as an important line of defence against cognitive decline and dementia.