Overcoming past challenges may require integrating traditional population science tools with innovative biomarker measures in a precision medicine framework.
Study: Diets to promote healthy brain aging. Image credits: Tatyana Baibakova / Shutterstock.com
From a recent study published in Nature Reviews Neurologyresearchers are investigating the role of nutrition in preventing cognitive decline and dementia.
What influence does diet have on the risk of dementia?
Dementia is a leading cause of mortality and morbidity around the world, with approximately 57.4 million people diagnosed with the disease in 2019. Researchers estimate that by 2050, more than 152 million people will suffer from dementia.
Despite these predictions, up to 40% of dementia cases could be prevented or delayed by controlling modifiable risk factors such as diet. A healthy diet can reduce the risk of many health problems, such as type 2 diabetes and high blood pressure, both of which are also linked to dementia.
Although disease-modifying therapies for Alzheimer’s disease (AD) have the potential to improve patient outcomes, these treatments can strain healthcare systems and increase health disparities. It is therefore crucial to develop effective prevention strategies at the individual and population level.
Dietary patterns and cognitive health
Numerous observational studies have linked the Mediterranean diet, which is characterized by high intakes of fish, poultry, olive oil and plant foods and low consumption of red meat and alcohol, with slower cognitive decline and a reduced risk of dementia.
Clinical studies have also reported cognitive benefits associated with the Mediterranean diet for individuals at high cardiovascular risk when supplemented with nuts or olive oil. Similarly, a meta-analysis found associations with better memory and global cognition; however, mixed results were observed for attention and executive functions.
The Dietary Approaches to Stop Hypertension (DASH) diet, which focuses on the consumption of lean proteins, nuts, whole grains, low-fat dairy products, fruits, and vegetables while limiting alcohol, saturated fat, and red meat, has been associated with limited cognitive benefits in observational studies. In clinical trials, the DASH diet alone did not improve cognition; however, significant benefits were observed when combined with aerobic exercise.
The Mediterranean-DASH Intervention for Neurodegenerative Delay (MIND diet) combines Mediterranean and DASH diets, emphasizing neuroprotective foods such as green leafy vegetables, nuts, and berries and limiting unhealthy food items such as red meat and fried foods.
Observational studies have produced mixed findings, with some reporting slower cognitive decline and others not observing significant benefits from the MIND diet. Furthermore, clinical trials have reported no significant cognitive improvements between MIND and comparison diets after three years.
Pro-inflammatory diets high in fried foods and red meat increase the risk of adverse cognitive outcomes, while anti-inflammatory diets high in fruits and whole grains have protective effects. Observational studies consistently linked pro-inflammatory diets to cognitive decline.
The plant-based diet has been shown to reduce the risk of dementia in vegetarians and slow cognitive decline in African Americans. In comparison, the Nordic diet, which is rich in berries, whole grains, fish, vegetables and canola oil, was associated with less cognitive decline among older adults with high adherence.
Biological mechanisms
Healthy diets such as the Mediterranean diet are associated with reduced accumulation of amyloid-β and tau proteins, both of which are biomarkers for AD, less brain atrophy and a slower volume decline of the hippocampus. In comparison, high amounts of saturated fats and sugars increase the burden of AD biomarkers.
Healthy nutrition supports cardiovascular health, which reduces the risk of dementia. Similarly, Mediterranean and DASH diets have been shown to reduce white matter lesions and cerebral infarctions, improve vascular function, and reduce endothelial dysfunction. However, there is mixed evidence about the long-term benefits of diets like the MIND diet.
A dysfunction in the brain’s energy metabolism contributes to cognitive decline. In recent studies, the Mediterranean diet has been shown to support glucose metabolism in the brain, limit declines in energy efficiency, reduce oxidative stress and improve antioxidant markers. DASH and vegetarian diets also reduce lipid peroxidation and improve antioxidant defenses.
Chronic inflammation affects brain health and cognitive aging, which is reduced after following the Mediterranean and DASH diets. The Mediterranean and MIND diets can also promote ‘epigenetic rejuvenation’, which slows biological aging. The health of the gut microbiome may also be involved in cognition; However, additional studies are needed to confirm this association.
Future perspective
Previous dietary trials for dementia prevention have shown mixed results due to design limitations such as participant selection, intervention intensity, and cognitive assessments. Thus, future studies are needed that include risk groups, personalized diets, longer durations and advanced biomarkers. Furthermore, developing broader and scalable interventions and efforts to engage underrepresented groups can increase the relevance and diversity of studies.