Diet and physical activity have been reported as independent risk factors for dementia, but few published studies have investigated the interactive effects of the two on dementia risk. Understanding their synergism could help shape more effective prevention strategies. Therefore, we assessed the potential interactions between MIND diet adherence and physical activity on the long-term risk of incident dementia in the population-based Rotterdam Study.

Between 2009–2013, 5016 participants of the population-based Rotterdam Study were recruited (mean age 69.76 years, 57.9% women). All participants filled in questionnaires regarding their adherence to the MIND diet and time spent on moderate to vigorous physical activity (Metabolic Equivalent of Task [MET] hours per week). Participants were subsequently followed for incident dementia until January 1, 2021. We applied multivariable Cox regression models to assess interaction on both additive and multiplicative scales.

Median values were 7.5 for the MIND diet score and 28.0 for MET hours per week. Of all 5016 participants, 2718 (54.2%) adhered to a high MIND diet score (≥7.5), and 2513 (50.1%) reached at least 28.0 MET hours per week. During a mean follow-up of 6.6 years, 365 participants (7.8%) developed dementia. Both higher physical activity and higher MIND-diet score were independently associated with a lower risk of dementia, but there was no significant interaction on the additive scale (RERI [95%CI]=-0.42 [-1.26 to 0.12]), nor on the multiplicative scale (HR _interaction =0.71 [0.46–1.09]). Sex-stratified analysis suggested a negative interaction between exposures in women, but not in men.

Better adherence to the MIND-diet and higher levels of physical activity were each associated with a reduced risk of dementia, but overall there was no indication that their joint effects were greater than the product or sum of their individual parts. Potential sex differences warrant further exploration in different populations.