March 14, 2023

expert reaction to observational study on Mediterranean diet and risk of dementia

An observational study published in BMC Medicine looks at adherence to a Mediterranean diet and risk of dementia.

Dr Annette Creedon RNutr, Nutrition Manager, British Nutrition Foundation, said:

“This study aimed to investigate associations between adherence to a Mediterranean diet and incidence of dementia. The study also aimed to explore the interaction between diet and genetic risk for dementia, by looking at all the genes known to be related to risk of dementia. Data from just over 60,000 participants from the UK Biobank data set were included in the study and were followed to determine whether there was a diagnosis of dementia during the follow-up period (a mean of 9.1 years).

“The findings may suggest that a high adherence to a Mediterranean diet is associated with a lower risk of incident all-cause dementia. Findings suggested that those with a higher Mediterranean diet adherence score were more likely to be females, have a BMI within the healthy range, have higher educational level and be more physically active than those with lower adherence scores. There was no significant interaction between the known genetic risk of dementia and Mediterranean diet adherence, suggesting similar associations between Mediterranean diet adherence and dementia risk irrespective of genetic risk. 

“Dementia should not be seen as a natural or inevitable part of ageing and there is growing awareness that lifestyle factors and not just genetics, play an important role in reducing the risk or delaying the onset of dementia.  Although there is no clear evidence that dementia can be prevented, this study supports existing evidence that a healthy diet and lifestyle can reduce the risk of developing dementia. It may be that the observed benefits in this study were due to the participants having an overall healthy dietary pattern rather than being due to the Mediterranean diet specifically. The Mediterranean diet scores were derived from data that was self-reported by participants and many of the participants only completed one or two recalls, hence, the calculated Mediterranean diet scores may not be fully representative of participants’ usual dietary intake. Also, it was not possible to obtain accurate intake data for all components of a Mediterranean diet such as the amount of olive oil consumed. 

“Current advice for reducing the risk of developing dementia includes eating a healthy diet, achieving and maintaining a healthy weight, exercising regularly, drinking alcohol in moderation, stopping smoking and keeping blood pressure at a healthy level. A number of these factors were evident in those participants with a higher Mediterranean diet adherence; however, it does not indicate that an individual can only acquire these benefits by adhering to the Mediterranean diet over another healthy dietary pattern.”

Prof Jane Murphy, Professor of Nutrition, Bournemouth University, said:

“This is well conducted research that draws on recognised robust UK dataset to provide new findings.

“It strengthens the importance of a healthy diet to reduce risk of dementia, where genetic makeup is not an influencing factor. The research shows diet quality is likely to be an important modifiable factor to help reduce the risk of dementia and improve health and wellbeing overall.

“The findings are limited by a dataset that reflects those following healthier lifestyle, from higher socioeconomic status and white British or Irish groups.

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

Dr Duane Mellor, Registered Dietitian and Senior Lecturer, Aston Medical School, Aston University, said:

“This is an interesting study looking to explore how peoples reported diets match to two scores used to assess Mediterranean Diet adherence in a large group of British people as part of the UK Biobank study. Although this study looked at around 1/2 million people, this study included only 60000 of this group who were over 60 years and identified as being white.

“The methods used to assess Mediterranean Diet score were limited and had largely yes/no answers, with one score (MEDAS) including ‘Sofrito’ (a dish of fried tomatoes with onions and garlic), which is commonly eaten in Spain but less so in the UK and may be difficult to identify from a food questionnaire designed to record a British dietary intake. This highlights the challenges of using these types of scoring systems to assess dietary quality as they are designed for particular eating habits, which may not translate internationally. The other scoring system – of an issue with PYRAMID score was less specific about foods like this, but include potatoes which tend to be eaten quite differently in the UK compared to the Mediterranean. However, the PYRAMID score did not show a clear link with Mediterranean diet and dementia.

“Although it is interesting to suggest that a higher MEDAS score was associated with a lower risk of dementia, it does not cover some of the social aspects of food which have been describe by UNESCO as intrinsic aspects of the Mediterranean diet, which include eating socially, which other studies have highlighted as important, that the Mediterranean way of eating is not just about food on plates, its about the social interactions linked to food and people who socialise more have lower risk of dementia and other conditions.

“When considering the implications of this type of work, we need to acknowledge that this analysis was only a small subsection of the UK Biobank cohort and did not include the diverse range of cultures, heritage and ethnicities that live in our society. We need to consider how a Mediterranean type diet can be adapted to foods available and eaten in the UK, so that inclusive messages about eating healthily can be developed which include the importance of the social aspects of sharing and eating food with others.”

Prof David Curtis, Honorary Professor, UCL Genetics Institute, said:

“This observational study finds that UK Biobank participants who adhere more closely to a “Mediterranean” diet tend to have a moderately lower risk of developing dementia. However it is not clear that this does not reflect the fact that they may have a generally more healthy lifestyle. Thus, it is not clear that such a diet itself reduces dementia risk, although it is plausible that it might do so. It is important to note that the study concerns all forms of dementia, not specifically Alzheimer’s disease. In my opinion if there is an effect of diet then it is more likely to be on cardiovascular health in general and hence to impact dementia due to vascular disease rather than Alzheimer’s disease. It is also disappointing that the researchers chose to exclude participants who were not white. I do not see any justification for excluding ethnic minority participants. Even if there were problems using them for the genetic aspects of the study it would still have been possible to see whether diet was associated with dementia risk in non-white participants.”

Dr Susan Mitchell at Alzheimer’s Research UK, said:

“There is a wealth of evidence that eating a healthy, balanced diet can help reduce the risk of cognitive decline. But evidence for specific diets is much less clear cut. 

“This new, large study adds to this overall picture, but it only drew on data from people with White, British or Irish ancestry. More research is needed to build on its intriguing findings, and uncover whether these reported benefits also translate to minority communities, where historically dementia has often been misunderstood and highly stigmatised, and where awareness of how people can reduce their risk is low.

“While there are no sure-fire ways to prevent dementia yet, a diet rich in fruit and vegetables, along with plenty of exercise and not smoking, all contribute to good heart health, which in turn helps to protect our brain from diseases that lead to dementia.”

‘Mediterranean diet adherence is associated with lower dementia risk, independent of genetic predisposition: fndings from the UK Biobank prospective cohort study’ by Oliver M. Shannon et al. was published in BMC Medicine at 01:00 UK time on Tuesday 14^th March.

DOI: 10.1186/s12916-023-02772-3

Declared interests

Dr Annette Creedon: Funding to support the British Nutrition Foundation’s charitable aims and objectives comes from a range of sources including membership, donations and project grants from food producers and manufacturers, retailers and food service companies, contracts with government departments; conferences, publications and training; overseas projects; funding from grant providing bodies, trusts and other charities.  Further information about the British Nutrition Foundation’s activities and funding can be found at http://www.nutrition.org.uk/aboutbnf/.

Dr Duane Mellor is a dietitian and member of British Dietetic Association.

Prof David Curtis: “No conflicts.”

For all other experts, no reply to our request for DOIs was received.