Diet, lifestyle and brain health

By Shireen Kassam

Cognitive impairment refers to a decline in brain function, including forgetfulness, poor concentration and difficulty making decisions, which can then lead on to dementia. The most common types of dementia are Alzheimer’s disease and vascular dementia.

The greatest global challenge for health and social care in the 21st century

Currently more than 55 million people live with dementia worldwide and there are nearly 10 million new cases every year. In 2019, the estimated total global societal cost of dementia was US$ 1.3 trillion, and these costs are expected to surpass US$ 2.8 trillion by 2030 as both the number of people living with dementia and care costs increase.

In the UK, almost 1 million people are living with dementia. This number is expected to rise to 1.4 million by 2040, resulting in costs of up to £90 billion annually. Most of these costs are related to family and social care rather than medical care.

What is driving the development of dementia?

Although there are genetic factors that increase a persons risk of developing dementia, these genetic factors account for less than 10% of cases. Instead, the development of dementia is driven by the same mechanisms as other chronic conditions, namely inflammation, dyslipidaemia, oxidative stress, insulin resistance and an unhealthy gut microbiome. Healthy lifestyle habits are able to address these key mechanisms and chronic conditions through risk factor modification and help prevent or delay the condition. Even in individuals with a higher genetic predisposition, healthy lifestyle habits can significantly reduce the future risk of developing dementia.

Forty-five percent of cases could be prevented or delayed

The Lancet commission on dementia initially reported that 40% of cases could be prevented or delayed by addressing 12 lifestyle-related factors; tobacco smoking, physical inactivity, depression, hypertension, obesity, diabetes, hearing loss and social isolation, excessive alcohol consumption, air pollution, attaining a good level of education and traumatic brain injury. In 2024, the Lancet commission provided an updated report adding two further risk factors; visual loss and high LDL-cholesterol. With these 14 risk factors it is now predicted that up to 45% of cases of dementia could be prevented or delayed.

The 2024 report specifically recognises the importance of healthy diets with a focus on the Mediterranean and MIND (Mediterranean-DASH diet Intervention for Neurodegenerative Delay) diet. The onset of Alzheimer’s disease (AD), the commonest type of dementia, is preceded by a long pre-clinical phase, as long as 15 to 20 years. This long pathological process offers opportunities for prevention. Another interesting observation made in the Lancet Commission report is that cognitive reserve i.e. preservation of cognition or everyday functioning, can be increased or maintained despite the presence of brain pathology and neuropathological changes associated with dementia. Early-life factors, such as less education, affect the resulting cognitive reserve. Midlife and old-age risk factors influence age-related cognitive decline and triggering of neuropathological developments.

Preventing dementia by addressing chronic health conditions

Dementia shares similar risk factors as cardiovascular disease (heart attacks and stroke). Those with high blood pressure, high cholesterol, type 2 diabetes and higher body weight are at significantly increased risk of developing dementia later in life. In fact, dementia has been termed ‘type 3 diabetes’ because of the association with insulin resistance. Addressing cardiometabolic risk factors through a healthy lifestyle approach is a very effective way to prevent dementia.

An analysis from the Whitehall study of UK British civil servants included data from 7899 participants and reported the association of cardiovascular health at age 50 with the incidence of dementia using the Life Simple 7 (now amended to 8 factors) cardiovascular health score devised by the American Heart Association. After a median follow-up of 25 years, the results demonstrated that the better the cardiovascular health score at age 50 years the lower the risk of dementia. For each 1-point increment in the score (14 points in total) there was a 11% reduction in the risk of dementia demonstrating that control of cardiovascular risk factors provides a powerful tool for prevention of dementia in later life.

A further analysis from the Whitehall study cohort assessed the association between underlying chronic conditions, termed multi-morbidity, and the risk of dementia after 32 years of follow up. The presence of two or more chronic conditions, was associated with a 2.4-fold increase in risk of dementia. The younger the onset of the chronic conditions the higher the risk of dementia with the strongest association at age 55 years. The commonest chronic conditions impacting risk were hypertension, depression, coronary heart disease and diabetes.

What is a healthy diet for prevention of dementia?

In general, diet patterns centred around healthy plant foods whilst being low or avoiding animal-derived and processed foods are best for preventing chronic diseases, including dementia. This includes diet patterns such as the Mediterranean, DASH (Dietary Approach to Stop Hypertension), MIND and mostly plant-based diets. Diets high in animal and processed foods and low in plant foods increase inflammation and oxidative stress, promote lipid and glucose dysregulation and result in insulin resistance. In contrast, healthy plant-based diets have been associated with lower levels of inflammation and are packed full of antioxidant compounds that help counteract different types of cellular stress, whilst promoting insulin sensitivity and a healthy gut microbiome.

What do we know about plant-based diets (vegetarian and vegan) and risk of dementia?

There are limited data on fully plant-based diets and risk of dementia. The only study we had for a while was a preliminary report from the Adventist Health Study suggesting that meat eaters had a significantly higher risk of developing dementia compared to vegetarians. A  more recent publication analysed data from the prospective Tzu Chi Vegetarian Study. It included data from 5710 participants who were aged 50 years or older at the time of recruitment in 2005 and followed till 2014. The participants were all Buddhist volunteers, 3154 were non-vegetarian and 1737 were vegetarian. During the average follow up of 9.2 years there were 121 cases of dementia (37 vegetarians and 84 non-vegetarians) identified and vegetarians had a 33% reduction in the risk of dementia. Subgroup analysis found that vegetarians were specifically protected against dementia under the age of 75 years.

An updated analysis of causes of death of participants in the Adventist Health Study-2 found that people consuming meat-free diets, including vegans, had a lower risk of premature mortality (<65 years), mainly due to the lower risk of conditions such as heart and kidney diseases and type 2 diabetes. However, by the age of 85 years this advantage had disappeared because of a weak association with an increased risk of neurological conditions, including dementia, stroke and Parkinson’s disease. It is not entirely clear how to interpret these findings, but one suggestion is that lower lifelong intakes of long-chain omega-3 fatty acids could adversely impact brain health late in life.

Which foods are best to avoid or reduce in the diet?

Higher intake of saturated fat is associated with an increased risk of dementia. Saturated fat in the diet comes predominantly from animal foods and the consumption of processed red meat seems to be particularly bad for brain health. Diets high in refined sugars, especially sugar-sweetened beverages, adversely affect brain health. Even artificially-sweetened beverages may be detrimental because of associations with higher risks of obesity, type 2 diabetes, hypertension and cardiovascular disease.

Which foods and nutrients are particularly good for preventing dementia?

The best foods for brain health are the brightly coloured fruit and vegetables with particular benefits for consuming leafy greens and cruciferous vegetables and berries. Intervention studies have shown that eating more fruit and vegetables can improve memory and attention at all ages of life.

Fibre intake is correlated with lower risk of many chronic diseases, including those that increase the risk of dementia, such as type 2 diabetes and high blood lipids. Fibre also benefits the gut bacteria, which then can make short chain fatty acids needed for brain hormone production and for reducing inflammation. In a Japanese cohort of 3739 individuals, dietary fibre intake was inversely associated with risk of dementia. Those consuming the most, particularly soluble fibre, had a 26% reduction in the risk of developing dementia over the almost 20 year follow up. Similarly, in a US population study, fibre intake was associated with better cognitive function.

Eating fruit and vegetables that are high in flavonoids may be of particular benefit. Flavonoids are a class of polyphenols representing more than 5,000 bioactive compounds that are found in a variety of fruit and vegetables, including grapes, berries, apples and in tea. Several studies have reported a beneficial effect of flavonoids for preventing cognitive decline, reducing the risk by around 20%. One reason why polyphenols in general may be beneficial for brain health is because they lead to the generation of beneficial bioactive compounds by the gut microbiota that can be detected in the blood and are associated with a reduced risk of cognitive decline.

Higher intakes of carotenoids from yellow/orange vegetables and dark leafy green have also been found to protect brain health. A study that followed 927 elderly US residents for 7 years found that those consuming the most carotenoid-rich foods had a 48% reduction in the risk of developing dementia. Higher blood levels of carotenoids and other plant-derived antioxidants are also associated with a significant reduction in the risk of dementia.

The long-chain omega-3 fatty acid docosahexaenoic acid (DHA) is very important for the developing brain and has also been shown to be important in protecting the ageing brain. The brain is composed of around 50–60% fat and has a particularly high content of DHA. Regular consumption of fish appears to reduce the risk of dementia and it is thought that this is due to the high DHA content. Although the data on the role of DHA supplementation is not always consistent, it may be prudent for older adults on a plant-based diet and those at higher risk of dementia to take an algae-derived DHA supplement. We know that algae supplements raise blood levels to a similar degree to fish consumption.

Alcohol and risk of dementia

We have been wrongly convinced that light to moderate alcohol is good for health, especially the consumption of red wine. However, the prevailing narrative is now changing and it is generally accepted that there is no safe limit of alcohol to consume when it comes to optimising cardiovascular health and reducing the risk of cancer. The same applies to brain health. Studies have shown that even small amounts of alcohol can negatively impact the structure of the brain and contribute to an increased risk of dementia.

The importance of healthy lifestyle habits

All aspects of our lifestyle are important for prevention of dementia, not only diet. This includes regular physical activity, restorative sleep, stress management and maintaining healthy social connections. An analysis from the The Chicago Health and Aging Project, a population-based cohort study in the United States, assessed the impact of 5 healthy lifestyle habits on life expectancy and the risk of AD in 2449 men and women aged 65 years and older. A healthy lifestyle score was developed based on five modifiable lifestyle factors: a diet for brain health (Mediterranean-DASH Diet Intervention for Neurodegenerative Delay — MIND diet score), late life cognitive activities, moderate or vigorous physical activity (≥150 min/week), no smoking, and light to moderate alcohol consumption (women 1–15 g/day; men 1–30 g/day). Participants most adherent to a healthy lifestyle had a longer life expectancy and were more likely to spend these extra years without AD. Of note, the lifestyle score without including alcohol consumption was also associated with a lower risk of AD and mortality and therefore the advice remains that people who do not consume alcohol should not be encouraged to do so. Healthy lifestyles in general are independently associated with a lower risk of cognitive impairment and dementia, regardless of genetic risk or the presence of brain pathology determined at autopsy.

It’s never too late to adopt healthy lifestyle habits

This was demonstrated in the Finnish Geriatric Intervention Study to Prevent Cognitive Impairment and Disability (FINGER), which examined the effects of a two-year comprehensive lifestyle intervention in 1,269 adults (60–77 years old) at risk of developing dementia. One group received the following intervention: a diet intervention based on the Finnish Nutrition Recommendations (emphasises whole plant foods and minimises animal-derived and processed foods), regular aerobic exercise and resistance training, cognitively challenging computer programmes, and intensive management of metabolic and vascular risk factors. The second group received standard care (simply advice to eat healthily and exercise). After 2 years, the intervention group had a significantly higher score in overall cognitive performance.

The POINTER study is unique in scale, diversity and duration and reinforces the findings of the FINGER study. This large, multi-centre, randomised clinical trial enrolled more than 2,100 adults aged 60–79 at elevated risk of cognitive decline due to sedentary lifestyles, suboptimal diets, cardiometabolic risk, or family history. Participants were assigned to either a structured, high-support programme or a lower-intensity, self-guided programme. Both emphasised the same principles: a healthier diet modelled on the MIND diet (rich in plant foods with proven brain benefits), regular physical activity, cognitive and social engagement, and cardiovascular risk monitoring.

After two years, cognition improved in both groups, but gains were greater in the structured intervention, where regular meetings, coaching, and accountability helped people stay on track. The structured group showed significantly better improvements in global cognition, particularly in executive function, compared to the self-guided group. Importantly, the benefits were consistent across key subgroups, including those at genetic risk of Alzheimer’s disease.

Dr Dean Ornish has published the first randomised study of an intensive plant-based lifestyle intervention in people with mild cognitive impairment or early dementia. The intervention was similar to his previous studies with a 100% plant-based diet, regular physical activity, social support and stress management. Of note, a number of nutritional supplements were also used, including omega-3 fatty acids. 51 participants were enrolled, and the study lasted for 20 weeks. Compared to the control group in which no participants demonstrated improvement, the intervention group were more likely to have stable cognitive function or demonstrate significant improvements.

Conclusions

We have enough evidence to support the important role of a healthy plant-based diet alongside other health lifestyle habits for promoting brain health and preventing dementia. Lifestyle interventions not only reduce the risk of common chronic health conditions known to increase the risk of dementia, but also address the underlying pathogenic mechanisms at play in the development of dementia.