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The Mediterranean diet is one of the best eating patterns for lowering the risk of neurological disorders, a literature review of the impacts of nutrition on the development of neurodegenerative diseases has concluded.
Researchers from the University of Messina, Italy, analyzed more than 200 scientific studies on the bioactive compounds of the Mediterranean diet, including flavonoids, polyphenols and anthocyanins.
They focused on how these bioactive compounds affect the development of Alzheimer’s disease and Parkinson’s disease, the two most common neurodegenerative diseases globally.
See Also:Health NewsAccording to the World Health Organization, about 60 million people globally have either Alzheimer’s disease or Parkinson’s disease, both of which have no cure.
Separate research from The Lancet estimates that dementia cases, of which Alzheimer’s is the most common form, will triple by 2050 as life expectancies grow longer and populations in North America, East Asia and Western Europe age.
Inflammation, oxidative stress and excess reactive oxygen are known to play a significant role in the development and progression of neurodegenerative disorders.
As a result, the bioactive compounds associated with common foods in the Mediterranean diet, including extra virgin olive oil, were of particular interest to the researchers as many have anti-inflammatory and antioxidant properties that may postpone the development of neurodegenerative diseases.
“Because of their potential for neuroprotection, antioxidant and anti-inflammatory effects and mitochondrial homeostasis to resist neuroinflammatory disorders associated with mitochondrial dysfunction, bioactive compounds have attracted the interest of scientists,” the researchers wrote.
The researchers investigated studies on flavonoids – found in vegetables, fruits, nuts, seeds, tea, coffee and wine – and found their consumption can have several positive health effects, including a decreased risk of developing Parkinson’s disease.
“Their physiological actions, which include antioxidative, anti-inflammatory, anti-apoptotic and lipid-lowering qualities, are the reason for this,” they wrote.
The researchers added that certain flavonoids also have neuroprotective effects due to their ability to reduce presynaptic glutamate release and reassemble postsynaptic glutamate receptors, which are critical for healthy brain function.
“The potential beneficial effect of flavonoids in the brain appears to be linked to their ability to interact with glial signaling and intracellular neuronal pathways, triggering neuronal regeneration, increasing existing neuronal functions, protecting vulnerable neurons or influencing the cerebrovascular and peripheral system,” they wrote.
Among the most common group of flavonoids are anthocyanins, to which the researchers paid particular attention. Anthocyanins are responsible for the red, violet and blue colorings of many fruits and vegetables.
“Anthocyanins ameliorate oxidative stress by lowering free radical production and lipid peroxidation,” they wrote. “The complex mechanisms by which anthocyanins can directly scavenge free radicals, prevent the formation of reactive oxygen species… or encourage the release of antioxidant enzymes are what give them their antioxidant properties.”
The researchers said higher anthocyanin consumption might help to prevent the development of neurodegenerative diseases in old age due to the links between Alzheimer’s disease and cardiovascular and metabolic health.
Based on the literature review, the researchers also determined that anthocyanins lower the concentration of ions and inhibit proteins that regulate neuronal apoptosis, or cell death.
“They also protected against memory loss as assessed by behavioral tests and measurement of anxiety, memory and motor functions,” they wrote.
In a study in mice, the researchers said anthocyanin consumption appeared to be associated with diminished brain tissue damage caused by the build-up of proteins associated with Alzheimer’s disease.
“By causing damage to neurons and other biological components, oxidative stress and neuroinflammation cause neurodegeneration,” they said. “Anthocyanins influence these metabolic pathways, enhancing antioxidant and anti-inflammatory defenses as well as maintaining normal hippocampus function.”
See Also:Med Diet Adherence Associated with Lower Dementia RiskThe researchers also focused on the role of polyphenols, the most prevalent dietary antioxidant, in Alzheimer’s disease and Parkinson’s disease development.
Due to its high metabolic activity, the researchers said the brain is particularly susceptible to oxidative damage since it is the location of increased oxygen absorption but low levels of antioxidant enzymes.
“Oxidative stress and damage to brain macromolecules are inherent processes in neurodegenerative diseases,” the researchers wrote.
“The antioxidant properties of many polyphenols are purported to provide neuroprotection,” they added. “The impacts of polyphenols on cognition and neurodegenerative processes appear to be mediated via interactions with neuronal and glial signaling pathways that influence gene expression and interfere with cell death mechanisms.”
Polyphenols manifest their antioxidant properties by directly scavenging free radicals or indirectly enhancing the capacity of the body’s natural defense system.
In the case of Parkinson’s disease, the researchers found that polyphenol consumption inhibited the aggregation of a protein associated with the development of the disease.
The researchers also highlighted separate studies that found that dietary polyphenols may activate pathways associated with adaptive cellular stress responses, upregulate genes that regulate cellular oxidation-reduction levels and improve the cell’s natural defenses against oxidation.
“Additionally, one of the most important polyphenols in this field is resveratrol,” they wrote. “Resveratrol is a polyphenol that occurs naturally in red grapes, peanuts and many other plant species. Administration of resveratrol to transgenic mouse models of Alzheimer’s disease reduces behavioral impairments and aging-related central nervous system Aβ [a neurotoxin] deposition.”
The researchers also investigated the role of insoluble phenolic acids in preventing the onset of Parkinson’s disease and Alzheimer’s disease.
Extra virgin olive oil has 36 phenolic compounds, including tyrosol, hydroxytyrosols, oleocanthal, oleuropein and carotenes.
“These phenolic chemicals penetrate the brain and exert neuroprotective effects via antioxidant, anti-apoptotic, and anti-inflammatory mechanisms,” they wrote. “According to extensive research, hydroxytyrosol functions as a scavenger of reactive free radicals, resulting in neuroprotective effects on brain cells during oxidative stress.”
Regarding the effects of phenolic compounds on Alzheimer’s disease, the researchers also investigated a study that looked at the role of olive leaves.
“[One study] explored the effect of the administration of bioactive molecules of the polyphenol class from olive leaves on male mouse neurotrophic proteins,” they wrote. “In particular, the study suggests that nerve growth factor and brain-derived neurotrophic factor and glial cell line-derived neurotrophic factor are involved in Alzheimer’s disease pathology. The administration of these polyphenols exhibited a key role in synaptic growth and protected neurons from damage.”
While the researchers said plenty of scientific studies point to the great potential of bioactive compounds – both in diet and pharmaceuticals – in the prevention and treatment of Alzheimer’s disease and Parkinson’s disease symptoms, they added that more work still needs to be done.
“Current research suggests that more long-term, double-blind, randomized controlled trials on a large human population are required to promote the Mediterranean diet,” they concluded. “This might help determine whether better adherence to this diet can help avoid or postpone the development of neurodegenerative diseases.”