Table 1.
Summary of systematic reviews and meta-analyses exploring the association of adherence to the MedDiet, which is the most studied dietary pattern in the medical literature, with cognitive decline and/or incident dementia.
| First Author of the Review | Year | Type of Review | Total Sample Size | N and Type of Studies Included | Summary of Results |
|---|---|---|---|---|---|
| Sofi [43] | 2008 | MA | 133,626 | 2 cohorts (3 studies) | Higher adherence to the MedDiet was associated with a significant reduction in incident PD and AD (RR = 0.87; 95% CI = 0.80, 0.96). |
| Sofi [24] | 2010 | MA | 136,235 | 5 prospective cohort studies | Two-point increase in adherence to the MedDiet was associated with a significant reduction of neurodegenerative diseases (RR = 0.87; 95% CI: 0.81, 0.94). |
| Psaltopoulou [44] | 2013 | MA | 11,141 | 5 prospective cohort studies; 5 cross-sectional; 2 case control | High and moderate adherence to the MedDiet was associated with reduced risk for cognitive impairment and AD (RR = 0.60, 95% CI = 0.43–0.83). |
| Singh [27] | 2014 | SR + MA | 7285 | 5 prospective cohort studies |
Highest tertile of the MedDiet adherence was associated with less risk of cognitive impairment (MCI or AD) vs. the lowest tertile. In cognitively normal individuals, higher adherence to the MedDiet was associated with a reduced risk of MCI (HR = 0.73; 95% CI, 0.56–0.96) and AD (HR = 0.64; 95% CI, 0.46–0.89). |
| Cao [45] | 2016 | SR + MA | 8174 | 4 prospective cohort studies | MedDiet was significantly associated with reduced incident dementia (RR: 0.69; 95% CI: 0.57, 0.84). |
| Wu [46] | 2017 | SR + MA | 34,168 | 9 prospective cohort studies | The highest MedDiet score was inversely associated with the developing of cognitive disorders vs. the lowest category (pooled RR = 0.79, 95% CI: 0.70, 0.90). Median category of adherence was not significantly associated with cognitive disorders. Dose–response analysis indicated a trend of linear association of MedDiet score with the incident risk of cognitive disorders. |
| Loughrey [47] | 2017 | SR + MA | 41,963 | 15 prospective cohort studies; 2 RCT | Meta-analysis of cohort studies showed a significant association of MedDiet with episodic memory and global cognition but not working memory or semantic memory. Meta-analysis of RCTs showed that adherence to the MedDiet improved delayed recall, working memory, and global cognition, but not episodic memory, immediate recall, paired associates, attention, processing speed, or verbal fluency vs. controls. The strongest evidence suggests benefit on older adults’ global cognition. |
| Lourida [48] | 2013 | SR | 18,926 | 11 cohort studies (8 longitudinal, 2 cross-sectional); 1 RCT |
Higher adherence to the Mediterranean diet was associated with better cognitive function, lower rates of cognitive decline, and reduced risk of AD in 9 out of 12 studies, whereas results for MCI were inconsistent. |
| van de Rest [49] | 2015 | SR | 84,481 | 6 cross-sectional; 12 longitudinal; 1 trial; 3 meta-analysis | Better adherence to the MedDiet was associated with less cognitive decline, dementia, or AD, as shown by 4 of 6 cross-sectional studies, 6 of 12 longitudinal studies, 1 trial, and 3 meta-analyses. |
| Petersson [50] | 2016 | SR | 89,561 | 27 observational studies (16 longitudinal, 6 cross-sectional); 5 RCTs |
Most of studies showed an association of adherence to the MedDiet with better cognitive performance. Only 3 of 32 studies found no correlation between MedDiet and AD, 3 found no association between MedDiet and cognitive impairment, and 5 found no association between the MedDiet and cognitive function. |
| Hardman [51] | 2016 | SR | 59,928 | 13 prospective cohort studies; 5 RCTs |
Higher adherence to the MedDiet was associated with slower cognitive decline, reduced progression to AD, and improvements in cognitive function in the following specific cognitive domains: memory (delayed recognition, long-term, and working memory), executive function, and visual constructs. There are a number of methodological issues. |
| Aridi [52] | 2017 | SR | 88,419 | 6 cross-sectional; 23 prospective cohorts; 2 RCTS | Cross-sectional and cohort studies in non-Mediterranean regions showed mixed results. Cohort studies from Mediterranean countries and RCTs showed a beneficial effect of the MedDiet on cognitive function and prevention of AD and dementia. |
| Knight [53] | 2017 | SR | 44,733 | 2 cross-sectional; 2 cross-sectional/prospective; 11 prospective |
Conflicting results and conclusions regarding the efficacy of the MedDiet for age-related cognitive function. Disparity of neuropsychological assessment methods used appeared to be a plausible contributor to the lack of consensus among study findings. |
| Radd-Vagenas [54] | 2018 | SR | 1888 | 5 RCTs (one with 5 studies; total of 9 studies) | Results from 5 RCTS are mostly nonsignificant. Only 12.1% of individual cognitive outcomes significantly favored the MedDiet for cognitive performance. Nevertheless, the significant improvements in cognitive combined domains in PREDIMED, the most robustly designed study, warrant additional research. |
| Dinu [25] | 2018 | UR | 245,799 | 5 meta-analyses including 3 to 9 cohort, 3 cross-sectional, 1 case-control (11 analyses) |
Out of 11 analyses (9 comparing high vs. low adherence to MedDiet; one for each 2-point increased adherence; one for each 1-point increased adherence), 3 reported convincing evidence of benefit, 2 were highly suggestive of benefit, 3 were suggestive of benefit, 1 reported weak evidence, and only 2 reported no evidence. |
AD: Alzheimer’s disease; CI: confidence interval; HR: hazard risk; MA: meta-analysis; MCI: mild cognitive impairment; MedDiet: Mediterranean dietary pattern; PD: Parkinson’s disease; PREDIMED: Prevención con Dieta Mediterranea; RCT: randomized controlled trial; RR: relative risk; SR: Systematic Review; UR: Umbrella Review.