Dr. Oliver M Shannon, Human Nutrition & Exercise Research Centre, Newcastle University
When I was young, I loved to spend time with my grandad. He was full of energy, had a wicked sense of humour, and was always there when you needed him. He was in great health throughout most of his life, and he was still running half marathons well into his 70’s. However, when he was 85, my grandad had a stroke. Shortly after, he was diagnosed with dementia and his short-term memory began to decline. Over time, other bodily functions did too, and he sadly passed away in January of this year.
This is a short-hand version of my own personal experience of dementia. Millions of other people have a similar story. You may do too. Indeed, right now there are over 55 million people in the world living with dementia, placing a huge and unsustainable burden on individuals, their families and society at large.
Although promising findings are starting to emerge, at present, there are very few options available for treating dementia. As such, many researchers are focused on identifying ways to help people reduce their risk of developing this condition.
The 2020 Lancet Commission Report on dementia prevention outlined 12 modifiable risk factors, which collectively account for around 40% of dementia cases worldwide, and could be targeted by policy makers and individuals to help reduce dementia risk. These risk factors include low education levels, hearing loss, brain injury, high blood pressure, high intake of alcohol, obesity, smoking, depression, social isolation, physical inactivity, air pollution, and diabetes.
Although this report identifies a high intake of alcohol (a dietary factor) and conditions such as obesity and diabetes (which may be linked with diet) as key dementia risk factors, it is notable that consumption of an unhealthy diet as a whole is absent from the list of modifiable risk factor for dementia. This is despite mounting evidence that what we eat can impact brain health throughout the life course.
There are a few reasons why diet might not play a more prominent role in the Lancet Commission report. This includes the difficulties in defining what a healthy/unhealthy diet looks like, and the fact that not all studies have shown convincing links between diet and brain health. There is therefore a need for more research to help us understand whether what we eat can have a meaningful effect on dementia risk. Likewise, it is important to identify whether there are certain people who might benefit more or less from making changes to their diet.
For some time, we (and many others) have been interested in the potential health benefits of eating a Mediterranean-like diet, which is rich in healthy plant-based foods like fruits and vegetables, pulses, nuts, olive oil and also includes plenty of fish. Numerous studies, including the influential PREDIMED trial in Spain, have shown that eating a Mediterranean diet can improve cognitive (brain) function in older adults. Similarly, a handful of studies have suggested that eating a Mediterranean diet could help reduce the risk of developing dementia. However, the links between a Mediterranean diet and dementia risk are far from conclusive. Moreover, most studies to date have been fairly small and have provided limited insight into whether certain individuals (for example, those with different genetics) might respond differently to consumption of a Mediterranean diet.
To address some of these issues, we recently explored the associations between adherence to a Mediterranean diet and dementia risk in over 60,000 participants from the UK Biobank. Using dietary data from the participants, we were able to give each individual a score ranging from 0 to 15 to define how closely their diet matched the key features of a Mediterranean diet (those with higher scores had a more Mediterranean-like diet). We then used a statistical technique known as Cox proportional hazard regression to explore associations between the level of Mediterranean diet adherence and risk of developing dementia over a ~9 year period, whilst controlling for potential differences in factors such the education level and physical activity status of participants.
We found that individuals with higher adherence to the Mediterranean diet, as defined by one of the Mediterranean diet scores known as the MEDAS continuous score, had a 23% lower risk of developing dementia than those with lower adherence to a Mediterranean diet.
Interestingly, there were similar associations between Mediterranean diet adherence and dementia risk in individuals with higher and lower genetic risk for this condition. This suggests that, even for those with higher genetic risk, having a more Mediterranean-like diet could help reduce the likelihood of developing dementia.
Our study has a number of strengths, not least it’s size and the comprehensive way in which we defined genetic risk for dementia (using an approach called a polygenic risk score). However, no study is without limitations. Most notably, as this was an observational study, we cannot infer cause and effect from our findings.
Much more research is needed to identify the best diet that people could follow to try and reduce their risk of dementia. However, the findings from our study contribute towards a growing body of evidence to suggest that following a more Mediterranean-like diet could be an effective way to help ‘oil your cogs’ and reduce your risk of developing dementia.