Can eating the right diet prevent Alzheimer’s disease?

A growing body of research is looking at whether certain lifestyle factors contribute to our risk of Alzheimer’s disease (the most common cause of dementia), and whether we can delay or even prevent the onset of the disease altogether.

We know that some dementia risk factors are impossible to change, such as your age and genetic make-up.¹ However, according to the 2020 Lancet Commission on dementia prevention, some risk factors are modifiable, and by making various lifestyle changes, up to four in 10 cases of dementia could be prevented.²

In recent years, diet has been frequently studied as part of this research. Many experts preach the ‘healthy heart, healthy brain’ message,³ which would imply that eating a balanced diet, maintaining a healthy weight and exercising regularly could all help to lower your risk of dementia.

However, there is very little evidence to suggest whether there is a definitive link between diet and dementia.

To discover more about what the available evidence does tell us, we spoke to three experts in the field: Professor Peter Passmore, Professor of Ageing and Geriatric Medicine at Queen’s University Belfast, who has a special interest in cognitive decline and dementia; Simon Wheeler, a health scientist and Knowledge Officer for The Alzheimer’s Society; and Patrick Holford, founder and Chief Executive Officer of the Food for the Brain Foundation.
[rml_read_more]

Can food be used as a means to prevent the onset of Alzheimer’s disease?

“People have this mistaken idea that there’s nothing they can do to prevent themselves from getting Alzheimer’s dementia, but there is,” says Patrick Holford, CEO of the Food for the Brain Foundation.

Holford says you can “dementia-proof your diet and lifestyle” by making a series of changes to the way you live. This includes:

Controlling your weight
Lowering blood homocysteine with B vitamins
Controlling blood sugar and preventing diabetes
Achieving sufficient omega-3 fat intake
Eating a ‘Mediterranean’ diet with antioxidant rich fruit, vegetables and vitamin C
Controlling your blood pressure
Preventing depression, stress and a lack of sleep
Keeping physically, socially and intellectually active
Not smoking and not drinking alcohol excessively.⁴

Holford says B vitamins and omega-3 fatty acids “build a healthier brain”, and have proven to be extremely effective in improving cognition in randomised controlled trials.

In one study, participants with high homocysteine and sufficient omega-3 levels were given B vitamins, and they were then assessed for brain shrinkage and any changes on the Clinical Dementia Rating (CDR) scale.⁵

“[By the end of the study], there was 73% less brain shrinkage and nearly a third ended the trial with NO overall Clinical Dementia Rating – i.e. no longer clinically demented,” Holford said.

Holford says this study provides good evidence that B vitamins and Omega 3 fatty acids may help to slow cognitive decline. This can be achieved through eating a diet high in seafood, poultry, eggs, dairy products, nuts, legumes and leafy greens.

Eating a wide variety of fruits and vegetables also benefits the brain, as Holford explains: “Energy production creates ‘exhaust fumes’ called oxidants, which age your brain. Eating lots of fruit and vegetables, which are high in antioxidants and polyphenols, can therefore help to slow cognitive decline,” he said.

Reducing sugar intake and avoiding ultra-processed foods, which are “major promoters of dementia”, are also vital to lowering our risk, Holford says.

“This is because foods which are highly processed and high in sugar create insulin resistance, which means the brain cells can’t get the glucose that they need, depriving them of fuel,” he says.

The Mediterranean diet follows many of these key principles, which is why a lot of the research based around diet and dementia risk looks at this particular dietary pattern.

A poor diet isn’t the only risk factor for dementia though, and Holford says “as well as fuelling the brain, we’ve got to use it.” This includes socialising, exercising and engaging the brain in intellectual activity. He also highlights the importance of good sleep for brain recovery.

“Food isn’t medicine, food is food”

However, others are more sceptical about whether eating the right diet can stave off cognitive decline. Simon Wheeler, a Knowledge Officer for the Alzheimer’s Society, says we should be wary of treating food as medicine.

While a good diet has a whole host of health benefits, Wheeler says there is not enough evidence to definitively say whether a poor diet causes dementia and whether a good diet can prevent the disease.

“The evidence is not strong enough or precise enough to be to be able to say that one food or one nutrient has a really big effect all by itself,” he said.

“A lot of people aren’t particularly satisfied with this answer because we have this culture of wanting to control our health destiny by treating food as though it is medicine. But food isn’t medicine, food is food. We use it to stay alive and gain nutrients, but it doesn’t actively treat illnesses.”

Professor Peter Passmore, Professor of Ageing and Geriatric Medicine at Queen’s University Belfast agrees with this concept, but emphasises that taking control of your health is likely to lower your risk.

He said: “Your overall health is going to have some effect on whether you go on to develop Alzheimer’s disease. Cholesterol, inflammation and vascular disease are all going to have an impact on how healthy your brain is, so controlling these factors may help to reduce the risk of dementia.

“However, no single nutrient is going to prevent Alzheimer’s disease, there is no magic bullet. Anything that is going to work is going to be a composite of multiple factors.”

Dr Passmore also highlights the methodological challenges of studies which assess whether diet and dementia are linked.

“The evidence suggests, from a retrospective perspective, a healthy, nutritious diet is good for the brain, and that’s the way we practice at the moment. But finding an intervention study that has been going for long enough, that has looked at all the endpoints and all the relevant, conflicting factors properly, that’s where the difficulty is,” he says.

The methodological challenges of studies assessing whether diet and dementia are linked

Wheeler has voiced similar concerns, and explains that while some studies which look at dietary patterns and their effect on dementia have yielded hopeful results, there are many methodological challenges and confounding factors that come into play.

“The evidence we have does show an association between certain dietary patterns – such as the Mediterranean diet – and the likelihood of developing dementia many years later. However, we also have to account for confounding bias.

“The people who eat better are generally healthier, more affluent and have a whole load of other health related advantages, other than the fact they eat sun-ripened tomatoes and extra virgin olive oil.

“So, the massive challenge in nutritional epidemiology is to try and tease out these confounding biases. We have to try and establish whether the associations seen in a study are genuinely causal or if they are just a confounded association.

“When you’re doing a good quality study looking at the relationship between x and dementia risk, we often see a link in the crude data, but it’s difficult to know whether that association is causal or not. It’s not always a case of is it or isn’t it, but rather, to what extent is it?” he said.

Wheeler says that in order for a definitive link to be made between diet and dementia risk, we would need large studies that last around 20 years, which take participants in midlife and follow them up to see if they go onto develop dementia.

“The problem we have is that it’s near on impossible to recruit a million people in their mid-40s, randomise them to a specific diet and exercise regime and then expect them to stick with it, and follow them closely for 20 years. This would be hugely expensive and there would be massive problems with adherence,” he explains.

Given these methodological challenges, researchers often use people who already have mild cognitive impairment as participants in studies. By this point, however, it may be too late to stop dementia in its tracks.

Wheeler therefore concludes: “Unless you have really good lifetime cohort data, showing targeted exposures, young adult exposures, midlife exposures, and cognitive and comorbidity data all the way through, then it’s very hard to be able to say, based on empirical data, that optimising diet throughout the life course will reduce your risk of dementia.”

Even so, Wheeler says he “completely agrees” with the concept that prevention is better than a cure, and recommends eating a healthy, balanced and nutritious diet for all the health benefits it brings.

Professor Passmore, who is a practising consultant geriatrician, says for these reasons, he would also recommend patients eat a healthy and balanced diet to reduce their risk of dementia and improve their overall health.

However, for patients that already have prodromal (early) Alzheimer’s disease, there is one supplement that Professor Passmore recommends to his patients.

Can supplements help to reduce the risk of Alzheimer’s disease?

“In the clinic, the only supplement we recommend is Souvenaid,” says Professor Passmore.

Souvenaid is a nutritional supplement drink which is taken once daily. It contains a combination of nutrients important for the formation of synapses in the brain, including uridine monophosphate, choline, omega-3 fatty acids, phospholipids, vitamin C, vitamin E, selenium, vitamin B6, vitamin B12 and folic acid.⁶

Souvenaid is not a licensed treatment so it cannot be prescribed, but studies have shown that the supplement may be able to improve memory in people with mild Alzheimer’s disease.

To date, there have been four studies which have evaluated the impact of Souvenaid on cognitive function. The available research suggests that Souvenaid modestly improves memory and Clinical Dementia Rating scores.⁶

One independent study (which was funded by the European Union) followed up patients with prodromal Alzheimer’s disease for three years. This study showed that the primary endpoint, a selection of five measures from the Neuropsychological Test Battery, was significantly improved in those on Souvenaid compared to those on placebo.⁷

There was also significantly less brain shrinkage in those on Souvenaid, suggesting a biological mechanism for the improvement on cognition and overall function.⁶

Professor Passmore says his clinic recommends Souvenaid to patients as it is one of the only supplements which has shown potential to slow down cognitive decline. However, the Alzheimer’s Society has warned that these benefits are minimal, and have only been shown on a small group of people.⁷

The Society therefore advises patients to consult their doctor or talk with a practitioner at a memory clinic before buying the supplement. Particularly as since it is not a licensed treatment, patients will have to pay for the supplement out of their own pocket.

How important is our gut microbiome for brain health?

As well as eating a balanced diet and taking nutritional supplements (if necessary), Professor Passmore notes the importance of maintaining a healthy gut.

An increasing amount of studies are looking at the link between gut microbiome and brain health. One study, which was presented at the Alzheimer’s Research UK Conference 2022, identified new links between gut bacteria, inflammation and brain changes associated with Alzheimer’s disease.⁸

In the study, scientists took blood samples from 68 people with Alzheimer’s disease and a similar number of people without. By comparing the samples, the scientists found a distinct gut bacteria makeup in people with Alzheimer’s as well as more inflammation markers in their stool and blood samples.⁹

The researchers also treated brain stem cells with blood from each group, and found that they were less able to grow new nerve cells compared to those treated with blood from people without Alzheimer’s disease.⁹

The researchers therefore concluded that the inflammation associated with gut bacteria can affect the brain via the blood.

A study involving rats has shown similar results. When stool samples were taken from people with and without Alzheimer’s disease and transplanted into rats, the researchers found that the rats with gut bacteria from people with Alzheimer’s performed worse in memory tests, didn’t grow as many new nerve cells in areas of the brain associated with memory and had higher levels of inflammation in the brain.⁹

This research suggests there may be a link between gut microbiome and brain health. However, it is important to note that this is still an emerging research area and more studies will need to be performed before a definitive link can be drawn.

So what can we do to reduce our risk of dementia?

While evidence linking diet, gut health and dementia continues to evolve, experts still recommend eating a balanced diet, maintaining a healthy weight, and exercising regularly, as this will benefit not only the brain, but the whole body.

As well as diet, the Lancet Commission on dementia risk reduction cites 12 risk factors for dementia, some of which are entirely modifiable. These are:²

Lower education levels
Hearing loss
Traumatic brain injury
Hypertension
Alcohol
Obesity
Smoking
Depression
Social isolation
Physical inactivity
Diabetes
Air pollution.

Experts say that by making various lifestyle changes, such as treating hearing impairment, maintaining a healthy weight, and exercising and socialising regularly, you can significantly improve your chances of maintaining cognitive reserve, therefore reducing your risk of dementia.²

However, around six in 10 cases of dementia cannot be prevented. These cases are down to “age, genes and a whole load of other stuff that we don’t really understand,” says Wheeler.

But even for those cases which are not preventable, there is hope on the horizon.

Is there hope on the horizon?

After 20 years with no new Alzheimer’s disease drugs in the UK, we now have two potential new drugs in the space of one year – lecanemab and donanemab.

Both of these treatments have been shown to slow down cognitive decline, making them the first drugs to fundamentally alter the pathology of the disease in the brain.

Up until the arrival of these two anti-amyloid drugs, Wheeler says it felt like Alzheimer’s disease was “completely impenetrable”. Now, experts hope these new treatments could pave the way for a cure.

However, there are significant risks surrounding the safety of these two new drugs, and multiple participants who took part in the clinical trials which tested these drugs have sadly died.

Part two of this article will discuss whether these new treatments really do hail “the beginning of the end of Alzheimer’s disease.”

References

Loeffler DA. Modifiable, Non-Modifiable, and Clinical Factors Associated with Progression of Alzheimer’s Disease. J Alzheimer’s Dis. 2021;80(1):1-27. doi: 10.3233/JAD-201182. PMID: 33459643.
Gill et al. Dementia prevention, intervention, and care: 2020 report of the Lancet Commission. Livingston. The Lancet. 2020. Volume 396, Issue 10248, 413 – 446
Bilodeau, K. Healthy brain, healthier heart? Harvard Health Publishing. Available at: https://www.health.harvard.edu/blog/healthy-brain-healthier-heart-202107222551
Food for the Brain Foundation. Eight Ways to Upgrade Your Brain. N.D. Available at: https://foodforthebrain.org/8-ways-to-upgrade-your-brain/
Oulhaj A, Jernerén F, Refsum H, Smith AD, de Jager CA. Omega-3 Fatty Acid Status Enhances the Prevention of Cognitive Decline by B Vitamins in Mild Cognitive Impairment. J Alzheimer’s Dis. 2016;50(2):547-57. doi: 10.3233/JAD-150777. PMID: 26757190
Dementia Australia. Souvenaid – a dietary treatment for mild Alzheimer’s disease. 2020. Available at: https://www.dementia.org.au/sites/default/files/helpsheets/Helpsheet-DementiaQandA23-Souvenaid_english.pdf
Alzheimer’s Society. Souvenaid: I’m worried about my memory – should I buy this drink? 2020. Available at: https://www.alzheimers.org.uk/blog/souvenaid-im-worried-about-my-memory-should-i-buy-drink
Alzheimer’s Research UK. Gut health plays a role in Alzheimer’s development, new study says. 2022. Available at: https://www.alzheimersresearchuk.org/gut-health-plays-a-role-in-alzheimers-development-new-study-says/