Iliana Lourida, University of Exeter
As life expectancies across the world steadily increase, the world’s population is inexorably ageing. Too often, with age comes difficult health problems such as dementia or Alzheimer’s disease. These highly disabling conditions lead to deteriorating cognitive abilities, and little chance to lead an independent life.
The number of people affected is expected to increase considerably, reaching epidemic proportions – estimates place the number of people with dementia at around 115m by 2050. In the absence of cures, potential strategies that might prevent are vital, and these have focused on lifestyle factors, such as diet.
The Mediterranean diet has long been associated with improved health and reduced risk of chronic age-related diseases such as heart disease, stroke, Type 2 diabetes and dementia. Traditionally, it is comprised of high levels of olive oil as the main source of fats, lots of cereals, nuts, fruits and vegetables, moderate consumption of fish and dairy products, a little meat, and moderate consumption of alcohol, especially wine, usually during meals.
To more closely examine this long-held association, we undertook and recently published the first systematic review looking at the association between the Mediterranean diet and age-related cognitive decline.
Based on twelve reviewed studies, it seems that a diet more closely resembling the Mediterranean diet was associated with better cognitive function and slower cognitive decline. We also found that people adhering more closely to the diet reduced their risk of developing Alzheimer’s by 34%-40%.
An impressive benefit, but how does it work? Many studies have reported the potential of certain nutrients to ward off dementia and Alzheimer’s disease, and many of these nutrients are included in the traditional Mediterranean diet.
For example, clinical trials have shown improved cognitive test scores after subjects took vitamins, trace elements, beta carotene andfolic acid supplements. Other studies have presented favourable findings for the role of unsaturated fats and vitamin B-12 consumption. Typical elements of the Mediterranean diet like fruits and vegetables, wine, virgin olive oil and some herbs are rich in these substances, including vitamin C, E, B, carotenoids and flavonoids.
Oxidative stress in the body – rising levels of oxidising agents against antioxidants – is an aspect of ageing. Oxidative damage is often observed in the brain of patients with Alzheimer’s disease, for example, but those eating Mediterranean diets show reduced oxidative stress, which could partially explain their lowered risk of dementia.
The progression of Alzheimer’s disease has also been linked to inflammation – the olive oil, nuts and oily fish in the Mediterranean diet are powerful sources of monounsaturated and polyunsaturated fat (omega-3 fatty acids). These are the “good fats”, all with anti-inflammatory effects. A diet high in saturated fats on the other hand, such as found in butter, animal fats, sweets, and highly processed foods, may be related to impaired cognitive function and dementia by restricting the flow of blood through the arteries, or by the accumulation of β-amyloid proteins in the brain that are the hallmarks of Alzheimer’s disease.
However, the Mediterranean diet is more than eating your five-a-day, drizzling extra virgin olive oil on your salad and avoiding triple chocolate cookies during weekly meetings. It’s a combination of healthy eating habits and behaviours over a long period of time, and studies indicate that its benefits stem from synergistic interactions of its different components. It’s unlikely that any single nutrient accounts for neuroprotective properties – you can’t just, for example, eat more fish and live longer.
Research also suggests the Mediterranean diet effects other age-related chronic conditions: a large, recent trial in Spain showed that a Mediterranean diet supplemented with extra-virgin olive oil or nuts reduced rates of cardiovascular disease by 30% compared to a low-fat diet. High blood pressure, diabetes and high cholesterol levels in midlife have all been linked to increased risk of dementia. Of course, it’s also possible that older Mediterranean-eating adults also generally have a healthier lifestyle, exercise regularly and engage in social activities that in turn may protect them from dementia.
So while it’s not yet clear whether it’s diet alone or with other lifestyle factors that ward off cognitive decline, the evidence is growing that enjoying Mediterranean culinary traditions not only satisfy our taste buds, but may preserve those precious memories until our later years.
Iliana Lourida, PhD student, University of Exeter
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