Is dairy intake associated with less cognitive decline? A systematic review and meta-analysis of longitudinal studies

Introduction: With aging population, prevention of cognitive de- cline is a major concern in primary care. Nutrition is a modifiable factor that could have a clinical impact in this prevention. In par- ticular, the effects of the dairy intake on cognition are still contro- versial. We conducted a systematic review and meta-analysis on association between the dairy intake and cognitive decline or inci- dence of dementia with dose-response analysis. Methods: We included longitudinal studies with community-dwell- ing adults ≥ 18 years unselected on the basis of chronic conditions. Our primary outcomes were the decline of cognitive function as de- fined in studies and incidence of dementia at end of follow-up. We identified relevant literature through a systematic search of Em- base, Medline Ovid, Cochrane, Web of Science and Google Scholar from inception to end of July 2020. Two investigators conducted abstract and full-text screenings, data extractions, and risk-of-bias assessments using the Academy of Nutrition and Dietetics Quality Criteria Checklist (QCC). We performed a meta-analysis using a random-effects model. Results: We included 11 prospective studies with 46,896 partici- pants. We rated all studies at low risk of bias. Mean follow-up time was 11.7 years. Seven studies assessed cognitive decline through decrease in scores of various neuropsychological tests including MMSE (Mini-Mental State Examination). Three studies assessed dementia incidence using either MMSE threshold or DSM-IIIR/ DSM-IV criteria. Comparing highest vs. lowest dairy intake, we found no association between dairy and cognitive decline. (Sum- mary risk ratio-sRR=0.97; 95%CI 0.82, 1.16; 7 studies) although with large statistical heterogeneity (I2=76.75%). The dose-response anal- yses using g/day with 4 studies showed U-shaped curve, with low- est risk at approximately 120-130 g/day. We found an inverse asso- ciation between the dairy intake and dementia incidence (sRR=0.61; 95%CI 0.44, 0.86; I2 =43.65%; 3 studies)