Background Cognitive decline is the first outward sign of dementia and represents a major public health effect. Evidence suggests that dietary patterns are associated with cardiovascular and cerebrovascular risk factors. A high quality diet such as Mediterranean diet might protect against Alzheimer’s disease, but its association with age-associated cognitive decline has been less explored.

Aim The current analyses aim to examine the association between the adherence to a Mediterranean-style diet and 20 years of cognitive decline from age 43 years to 60–64 (>60) years in a prospective longitudinal population-based study.

Methods Participants were 1018 study members from the MRC National Survey of Health and Development (the British 1946 birth cohort) regularly followed up since birth in 1946 across their entire life. Cognitive functioning was measured at age 43 years and older than 60 years by tests of verbal memory (maximum words recalled 45) and timed visual search (maximum letter searched 600). The adherence scale to the Mediterranean diet was constructed with information from a 5-day estimated diet diary at both 36 and 43 years, using the Trichopoulou model (2003). Participants were divided into 3 groups of adherence to the Mediterranean diet (low, middle, and high tertiles) and an average early-midlife score was calculated. The confounding variables were social class of origin, childhood cognition, education, adult social class depression and other lifestyle behaviours such as smoking and physical activity. The associations between the adherence to the Mediterranean diet and change in cognitive tests were tested via multiple linear regression.

Results There was a significant association between a higher level of adherence to the Mediterranean diet in early midlife and a slower verbal memory over 20 years period from 43 to 60+ in a fully adjusted model β = 1.03 (95% CI 0.24, 1.83) compared to the lower level of adherence. This association maintained its significance even after adjusting for the early-midlife level of smoking and physical activity. A higher adherence to the Mediterranean diet did not show a significant protection for the visual search decline over the same time period.

Conclusion The results from these analyses suggest that higher adherence to the Mediterranean diet in early midlife is protective of verbal memory decline from mid to later life independent of other lifestyle behaviours such as smoking or physical activity. Public health interventions based on healthy dietary styles (such as Mediterranean diet) should be considered as important measures of defence against cognitive decline and dementia in later life.