Does diet influence dementia risk? What we know

Keeping fit and healthy can reduce the risk of dementia — and diet is a large part of keeping fit.

In a comment for MNT, Dr. Christopher Weber, director of global science initiatives at the Alzheimer’s Association, noted that:

“Research looking at the relationship between diet and cognition is well-established. There is strong evidence to suggest that what is good for the heart is good for the head, and we know a healthy diet is good for the heart.”

Some studies have suggested that a Mediterranean diet can improve cognitive function. This diet includes plenty of fruit and vegetables, nuts and seeds, olive oil and fish, with small amounts of dairy, eggs, and red meat, together with a moderate amount of red wine.

Recent research showed that a Mediterranean diet has associations with improved cognitive functioning and slowed the progression from mild cognitive impairment to dementia.

An alternative to the Mediterranean diet is the MIND diet (Mediterranean-DASH Intervention for Neurodegenerative Delay). The diet is similar but focuses on green leafy vegetables, other vegetables, nuts, berries, beans, whole grains, seafood, poultry, olive oil, and wine.

This diet highlights the importance of foods and nutrients that have an association with dementia prevention.

A problem with diet studies is that they are observational, and people usually assess their diet through self-reported questionnaires. However, researchers have demonstrated an association between these diets and improved cognitive function.

One study showed a substantially slower cognitive decline in those following the MIND diet. A 2021 study found a positive correlation between MIND diet score, cognitive resilience, and cognitive function.

Interestingly, the researchers found that improved cognitive function was independent of brain pathologies that post-mortems identified in participants.

Dr. Weber commented: “The Mediterranean diet and the MIND diet have been shown in clinical studies to be beneficial to brain and heart health. The Alzheimer’s Association encourages everyone to eat a healthy and balanced diet as a way to help reduce the risk of cognitive decline.”

Processed food is one of the current bad guys. Experts tell us to eat a balanced and varied diet containing plenty of fresh food to stay healthy. But could a diet high in processed food increase your dementia risk?

“There is […] strong evidence linking poor diet (for example, eating a diet high in unhealthy fats and sugar) and increased risk for dementia.”

– Dr. Christopher Weber

In animal models, a diet high in refined carbohydrates increases the risk of dementia and Alzheimer’s. A human study in France replicated this effect and confirmed that older participants who ate a daily snack high in refined carbohydrates were more likely to develop dementia.

Another study has linked processed meat products, such as sausages, salami, and bacon, with dementia. Regular consumption of processed meat increased the relative risk of all dementias by 44{cfdf3f5372635aeb15fd3e2aecc7cb5d7150695e02bd72e0a44f1581164ad809} and Alzheimer’s disease by 52{cfdf3f5372635aeb15fd3e2aecc7cb5d7150695e02bd72e0a44f1581164ad809}.

However, like all the other dietary studies, this was observational and the risks reported are relative rather than absolute. One expert commented that the results “would not persuade me to give up my breakfast bacon.”

Proponents of vitamin and mineral supplements often tout them as a way of compensating for a less than optimal diet, but is there any evidence that they might help combat dementia?

A recent study gave older male rats a processed food diet high in refined carbohydrates and found that their learning and memory skills suffered. Another group of rats on the same diet but with omega-3 supplements showed no memory problems.

The authors of the study explained their findings in terms of the inflammatory response provoked by processed foods. Scientists know that omega-3 resolves inflammation, which might explain the effect in the rats who received it.

However, there is little other evidence to suggest that supplements affect dementia. The WHO advises that a healthy diet and regular exercise will likely have more significant effects.

The link between alcohol and dementia is not entirely clear. While heavy alcohol consumption has strong associations with the development of dementia, the effect of moderate alcohol intake is still open to question.

The majority of studies show an association between low to moderate alcohol use and reduced risk of dementia, particularly for red wine drinkers.

Two systematic reviews, one of which analyzed results from 26 studies, concluded that reducing heavy alcohol use could be an effective dementia prevention strategy.

However, they also noted that those who abstained from alcohol entirely had a higher dementia risk than those who drank in moderation.

Therefore, it is possible that drinking in moderation may have some protective effect, but no observational study can exclude all other factors. It may be that those who drink moderately have a better diet, do more exercise, or are generally in better health.

One study into the effects of moderate drinking in older adults in New Zealand controlled for socioeconomic status but found no evidence for a link between moderate drinking and better health.

So perhaps that protective effect is just wishful thinking from those of us who enjoy an occasional drink!

Research has linked memory decline with inflammation, and this is an area that is attracting a lot of interest.

According to Prof. Tim Spector, Professor of Genetic Epidemiology, King’s College London and Zoe Study lead, “This fits with the ‘inflammaging’ theory that is gaining a lot of traction.”

There are links between inflammation and the gut microbiome. Several clinical studies have seen an association between the gut microbiome and dementia.

One cross-sectional study in Japan found a significant difference between the microbiome of people with dementia and those without the disease.

Those with dementia had a much lower number of Bacteroides, a species known to reduce inflammation. They also had much higher numbers of microbes (enterotype III) that have associations with dementia.

Two other studies back up these findings. One analyzed gut microbiome metabolites, finding that people with dementia had significantly different metabolites from those without the disease.

A second stressed the links between the gut microbiota and dementia development, observing effects on the microglia and cytokine release, which have implications in inflammation and dementia.

“There are large numbers of studies that are pointing in the same direction. People with dementia have sub-optimal microbiomes. The picture is of not only reduced numbers of species but also increased numbers of inflammatory species.”

– Prof. Tim Spector

The gut microbiome and diet have links, and this could be why the Mediterranean and MIND diets have shown positive effects in reducing dementia risk and progression.

“Reduced [microbiome] diversity and [more] inflammatory species are related to poor diet, generally low in fiber and diversity of plants,” Prof. Spector told us. “With elderly people, there’s often a tipping point, such as losing a partner. The diet reduces in quality and diversity. That can accelerate cognitive decline.”

He did, however, stress that there may be a reverse causality. People in the early stages of cognitive decline might reduce the quality of their diet and thereby accelerate the process.

“Studies of centenarians have found that they generally live in areas with a good food culture and lots of socializing,” he added. “It’s not about fats. It’s not about carbohydrates or calories, but can you get fresh, varied food? You need your gut microbes to keep your immune system suppressing inflammation?”

The short answer is probably; that diet may well play a part. Evidence is growing that a varied diet rich in plants will support a varied gut microbiome. And a varied gut microbiome helps to reduce the inflammation implicated in dementia.

“Poor diet harms microbes, which harms the immune system with these knock-on effects of cognitive decline. In dementia, inflammatory aging is the current theory. It’s partly triggered by the immune system which involves the microbes and diet.”

– Prof. Tim Spector

So until randomized control trials can prove how diet influences dementia, it is probably best to eat a diet that reduces the risk of heart disease and supports your microbiome, combining it with regular exercise.

The jury is still out on moderate alcohol consumption, but there is clear evidence that too much alcohol increases the risk of many health conditions, including dementia.

Dr. Weber concluded: “While we continue to learn more about lifestyle factors that have the greatest impact on our overall risk, there are things we can do today that may decrease our risk of cognitive decline as we age. Eating a heart-healthy diet, exercising regularly, and staying cognitively engaged are just a few.”