Diet, lifestyle and brain health
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 Dementia 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, around 900,000 people are living with dementia. One in 14 people over the age of 65 have dementia, and the condition affects 1 in 6 people over 80 years. It is estimated that by 2025, the number of people with dementia in the UK will be more than 1 million and by 2040, 1.6 million. The cost of dementia to the UK is currently £34.7 billion a year, which works out as an average annual cost of £32,250 per person with dementia. Nearly 85% 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 therefore able to address these key mechanisms 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.
Four out of 10 cases could be prevented or delayed: The Lancet commission on dementia 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 and traumatic brain injury. The onset of AD 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 to 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 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 (Mediterranean-DASH diet Intervention for Neurodegenerative Delay) and a fully plant-based diet. 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 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.
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 and carbohydrates also appear to impair cognitive function both in the short-term and long-term, the latter in part due to the ability of sugar to increase inflammation and the risk of cardiovascular disease. Interestingly even artificially-sweetened beverages, in some but not all studies, have been associated with an increased risk of dementia.
Which foods and nutrients are particularly good for preventing dementia? The best foods for brain health are the brightly coloured fruit and vegetables. Vegetables, particularly green leafy, appear more important than fruit in protecting against dementia with the exception of berry consumption, which appears highly protective against cognitive decline. A recent study highlighted the importance of eating fruits and vegetables early in life to prevent later cognitive impairment. This study recruited more than 3000 participants in the United States aged 18–30 years in the 1980’s and followed them for 25 years, regularly documenting their dietary intake. It found that those consuming the most fruits and vegetables at a younger age had the best cognitive function later in life. Vegetable consumption had a greater effect than fruits, with nutrients such as lycopene from tomatoes/red vegetables and beta-carotene from yellow /orange vegetables having the best effect. Overall, it seemed that it was the fibre intake that was responsible for much of this beneficial effect on brain health.
Fibre intake is correlated with lower risk of many chronic diseases that increase the risk of dementia, such as type 2 diabetes and high blood lipids. Fibre also benefits 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.
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 fruits 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 reasons why polyphenols in general may be beneficial for brain health are 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 there are conflicting data on the role of DHA supplementation, it may be prudent for those on a plant-based diet 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 decline in cognitive function.
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.
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.
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.
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