Mediterranean diet linked to lower dementia risk, but experts flag research must be more inclusive

15 Mar 2023 --- Participants with high adherence to a Mediterranean-like diet had up to 23% lower risk for dementia, independent of genetic risk. However, the research team and critics point to limitations as the analysis focused on white participants over 60.

“This study contributes to a growing body of evidence to suggest that eating a more Mediterranean-like diet could help reduce dementia risk,” lead author Dr. Oliver Shannon, lecturer in human nutrition and aging at Newcastle University, tells NutritionInsight. 

“We hope this work will help strengthen the case for dietary interventions to be included in future dementia prevention trials, which will provide insight into the causal relationships between diet and dementia risk.” 

Mediterranean diets are rich in nuts, seeds, fruit, vegetables, whole grains, legumes and olive oil. 

Mediterranean diet adherence 
Dr. Duane Mellor, registered dietitian and senior lecturer at Aston Medical School, UK, warns that the study’s methods to assess Mediterranean diet adherence were limited as it had yes/no answers and included scores for foods not commonly eaten in Spain. 

“This highlights the challenges of using these scoring systems to assess dietary quality as they are designed for particular eating habits, which may not translate internationally,” says Mellor.The Mediterranean diet includes daily consumption of fruit, vegetables, legumes, olive oil, seafood and nuts.

Shannon counters that the scoring systems selected are among the best available. 

“For example, they use clearly defined criteria to score each food group of the Mediterranean diet, which allows comparisons between the results of other studies and improves translation of findings into the real world.”

Limited diversity of participants  
Jane Murphy, professor of nutrition at Bournemouth University, the UK, agrees with the authors that the database used is limited as participants follow healthier lifestyles, have a higher socio-economic status and are from white British or Irish groups. 

“The findings do not reflect wider UK society and under-represented groups in the UK dataset, including those from diverse ethnic communities and lower socio-economic groups. More research is needed on the impact of a healthy diet and reduced dementia risk in these population groups.” 

Shannon agrees, “We are also keen to conduct further randomized controlled trials examining the effects of Mediterranean diet intervention on dementia risk. A key focus here will be to ensure recruitment and representation of individuals from various ethnicities and backgrounds.” 

In a recent study, the Mediterranean diet was also linked to reducing Alzheimer’s disease-related biomarkers. 

Study outcomes
The research team analyzed data from 60,298 individuals from the UK Biobank who had completed at least one dietary assessment. Hospital inpatient records and death registries provided information on dementia cases. The results are published in BMC Medicine.

The authors scored participants’ diets based on the resemblance to daily dietary targets in Mediterranean diets. 

Participants were followed for over nine years. The researchers also estimated participants’ polygenic risk, a measure of the different genes related to the risk of dementia. 

Vitamin D has also been researched on its effects on delaying dementia, although critics point out limitations. 

Lifestyle factorsShannon notes the researchers are keen to conduct further randomized controlled trials on the effects of Mediterranean diets on dementia risk.
The authors note that the study’s observational design makes it difficult to draw causal inferences. Moreover, measuring dietary intake was a significant challenge as many participants only completed one or two 24h recalls through online questionnaires. 

Shannon notes that various lifestyle factors associated with the Mediterranean diet could plausibly play a role in helping protect against dementia. 

Mellor agrees, “The Mediterranean way of eating is not just about the food on plates. It’s about the social interactions linked to food and people who socialize more have a lower risk of dementia and other conditions.”

Researchers warn that the benefits of a Mediterranean diet on cognitive health are diminished if people consume processed and other unhealthy foods. 

Further research needed 
Shannon notes that future investigations could look further into how other aspects of the Mediterranean lifestyle influence dementia risk.

Moreover, the interaction between diet and genetics on dementia risk warrants additional research, as findings were inconsistent across the sensitivity analyses. 

Shannon notes that it “is necessary to develop further scores which reflect the healthy eating guidelines of different countries, such as the Eatwell Guide in the UK, which may include more culturally relevant foods.”

Mellor concludes that “we need to consider how a Mediterranean diet can be adapted to foods available and eaten in the UK, so that inclusive messages about eating healthy can be developed, which include the importance of the social aspects of sharing and eating food with others.” 

By Jolanda van Hal