Abstract
BackgroundAs aging populations increase across the globe, research on lifestyle factors that prevent cognitive decline and dementia is urgently needed. Therefore, a systematic review was conducted to examine the effects of varying levels of milk intake alone or in combination with other dairy products on the outcomes of cognitive function and disorders in adults.MethodsA comprehensive search was conducted across 3 databases (PUBMED, CINAHL, and EMBASE) from their inception through October 2017. Prospective cohort studies and randomized controlled trials (RCTs) that enrolled adults were included. Studies with follow-up durations of less than 4 weeks and studies including schizophrenic patients were excluded. Two independent investigators conducted abstract and full-text screenings, data extractions, and risk-of-bias (ROB) assessments using validated tools. Studies were synthesized qualitatively using a strength of evidence (SoE) rating tool. A random-effects model for meta-analysis was conducted when at least 3 unique studies reported sufficient quantitative data for the same outcome.ResultsA total of 1 RCT and 7 cohort studies were included. One medium-quality small RCT (n = 38 participants) showed that only spatial working memory was marginally better in the high dairy diet group compared to the low dairy diet group. Two of the 7 cohort studies were rated as having a high ROB, and only 1 cohort study was rated as having a low ROB. There were large methodological and clinical heterogeneities, such as the methods used to assess milk or dairy intake and the characteristics of the study populations. It was impossible to conduct a dose-response meta-analysis because the studies utilized different categories of exposures (e.g., different frequencies of milk consumption or the amount of dairy intake). Thus, the overall SoE was rated as insufficient regarding the associations between milk intake and cognitive decline, dementia, and Alzheimer’s disease outcomes. Our meta-analysis of 3 cohort studies showed no significant association between milk intake and cognitive decline outcome (pooled adjusted risk ratio = 1.21; 95% CI: 0.81, 1.82; for highest vs. lowest intake) with large statistical heterogeneity (I2 = 64.1%).ConclusionsThe existing evidence (mostly observational) is too poor to draw a firm conclusion regarding the effect of milk or dairy intake on the risk of cognitive decline or disorders in adults.
Highlights
The American Diabetes Association’s (ADA) evidence-based practice guidelines, standards, and related recommendations and documents for diabetes care
Studies must have compared varying doses of milk intake, alone or in combination with other dairy products, and reported outcomes related to cognitive function, including any stage of dementia or any type of dementia (i.e., Alzheimer’s disease and vascular dementia)
This study indicated no significant association between milk intake and working memory, while a higher milk intake was associated with poorer verbal memory performance [32]
Summary
The American Diabetes Association’s (ADA) evidence-based practice guidelines, standards, and related recommendations and documents for diabetes care. The prevention of cognitive decline and dementia is an increasingly important public health priority due to the growth of the global elderly population [1]. Cognitive decline is a precursor to mild cognitive impairment (MCI) and is potentially the earliest clinical indicator of dementia [5, 6]. Subjective Cognitive Decline (SCD) refers to a self-experienced persistent decline in cognitive abilities in comparison with a prior normal status and independent of the objective performance on neuropsychological tests [9]. SCD can be diagnosed by several questionnaires of self-reported cognitive performance, such as the Mini Mental Status Examination (MMSE) and the Global Deterioration Scale (GDS) without the use of neuropsychological tests for objective assessment of cognitive function [10]. The international SCD Initiative Working Group has systematically identified 34 self-report SCD measures and has found wide variations in the definitions, cognitive domains, optimal items for each domain, item response options, and time frame across measures [12, 13]
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