Mediterranean Diet and Dementia: 12 Studies Reviewed
The first systematic review of the Mediterranean diet and brain health finds that in 9 of 12 studies, people who ate that way more closely had better cognitive function, slower decline and a lower risk of Alzheimer’s disease. The researchers at the University of Exeter are careful to say this does not yet prove cause and effect. Here is what they found, where olive oil fits in, and what it does not mean.
What the Exeter team did
A team at the University of Exeter Medical School, led by researcher Iliana Lourida and supported by the NIHR PenCLAHRC research collaboration in south-west England, published its review in the July issue of the journal Epidemiology. The university announced it in early September, and it has been picked up by the olive trade press this week.
A systematic review does not run a new experiment. It gathers every study that meets set criteria and looks for what they agree on and where they disagree. Until now, the evidence linking the Mediterranean diet with the aging brain had been a scatter of separate papers. The Exeter group found 12 that qualified: 11 observational studies, which follow people and compare their habits with what happens to them, and one randomized controlled trial.
| Question | What the review found |
|---|---|
| Cognitive function and decline | Better function and slower decline with higher adherence, in most studies |
| Alzheimer’s disease | Lower risk with higher adherence |
| Mild cognitive impairment | Inconsistent results |
| Overall | Positive association in 9 of 12 studies; trials still needed |
What it does not show
Lourida’s own summary is measured. The diet “may help to protect the ageing brain”, she said, but observational studies only provide suggestive evidence, and randomized trials are needed to confirm whether the diet actually protects against dementia. The review also flags gaps: the link with mild cognitive impairment and with vascular dementia needs more work.
That caution matters. People who eat a Mediterranean-style diet in these studies tend to differ in other ways too, in income, education, exercise and smoking. Good studies adjust for those differences, but no adjustment is perfect. That is exactly why the authors ask for trials rather than claiming a cure.
Where olive oil fits
In the Exeter description, a Mediterranean diet means more olive oil, vegetables, fruit and fish, and less meat and dairy. Olive oil is one ingredient of a pattern, not the active drug. Earlier work has looked at single foods: a Spanish analysis of older adults at high cardiovascular risk, published last year in the Journal of Alzheimer’s Disease, linked olive oil intake with better immediate verbal memory and walnuts with better working memory. Those are associations too, in one group of people.
For anyone deciding what to cook, the practical reading is simple and not very exciting:
- Use olive oil in place of butter and other animal fats, not on top of them.
- The pattern is the point: vegetables, pulses, fruit, fish and oil together.
- No single bottle, capsule or “brain” label is backed by this review.
We have covered this ground before, from what a Mediterranean diet actually is to an earlier study on the diet and Alzheimer’s. The difference this time is that someone has put the studies side by side and counted.
Expect this review to turn up on bottle neck tags and in sales pitches as “olive oil protects the brain”. It says nothing of the kind. It is about a whole way of eating, the evidence is mostly observational, and in Europe a bottle is only allowed to make the health claims the law approves. When a label promises more than the science, the label is the product being sold. Knowing how to read a health study is worth more than any premium.
This is general information, not medical advice. If you or someone close to you is worried about memory or thinking problems, talk to a doctor, who can look for treatable causes.
Sources
- University of Exeter: Research confirms Mediterranean diet is good for the mind (September 3, 2013, archived)
- Lourida I, et al. Mediterranean diet, cognitive function, and dementia: a systematic review. Epidemiology, 2013 (PubMed)
- Olive Oil Times: Mediterranean Diet Good for the Brain (September 9, 2013)