What is Neuroinflammation?

Neuroinflammation is the inflammatory response that occurs within the brain and/or spinal cord.¹ It’s quite a complex process that is mediated by microglia, which are resident cells of the brain that regulate brain development, maintenance of neuronal networks, and injury repair.¹ They are the primary source of proinflammatory cytokines, which are inflammatory signalling molecules.² Microglia are pivotal mediators of neuroinflammation and can induce or modulate a broad spectrum of cellular responses.² Alterations in microglia functionality are implicated in both acute and chronic neuroinflammatory responses.¹

Common Causes of Neuroinflammation

The most common causes of neuroinflammation include:

• Ageing - as we age, the body's ability to fight inflammation decreases, which can lead to increased inflammation within the brain and spinal cord. Research has shown that a healthy but aging brain has chronically increased levels of pro-inflammatory cytokines and reduced levels of anti-inflammatory cytokines, demonstrating that as we age, neuroinflammation is present.^3,4
• Chronic and sustained stress – can lead to the increased release of pro-inflammatory cytokines systemically and within the brain, leading to the increased risk of neuroinflammation.⁵
• Metabolic syndrome, obesity, and type two diabetes all are associated with increased inflammatory responses both systemically and within the brain, and are linked with the increased risk of developing neurodegenerative diseases.^6,7
• Environmental pollutants – frequent exposure to pesticides, heavy metals, and environmental pollutants is associated with the increased production of neuroinflammatory cytokines.^8-10
• Viral infections can lead to inflammation in the brain and spinal cord due to the immune response withing the central nervous system.¹¹
• Injury - trauma to the brain and spinal cord.¹²
• Neurological diseases – dementia, Parkinson’s disease, Alzheimer’s disease, and multiple sclerosis are all associated with increased inflammation within the brain.¹²

Inflammation and Oxidative Stress

Certain lifestyle habits can increase oxidative stress and inflammation, both systemically and in the brain. Oxidative stress occurs when the body cannot counteract and detoxify the damaging effects of free radical molecules, due to inadequate levels of protective antioxidants, and/or an excess of free radicals. This then creates an imbalance within the body and increases the risk for neuroinflammation.¹

Lifestyle factors that increase oxidative stress and inflammation:

• Smoking¹³
• Overconsumption of alcohol¹⁴
• Obesity, type two diabetes, and metabolic syndrome¹⁵
• Diets high in hydrogenated fats, high refined sugar, and processed foods¹⁵
• Sedentary lifestyle¹⁵
• Consistent poor-quality sleep¹⁶
• Exposure to heavy pollution, environmental toxins, pesticides, and heavy metals¹⁰

Stress and Neuroinflammation

Recent studies have found chronic stress can cause neuroinflammation through the activation of the resident immune cells in the brain, the microglia, to produce inflammatory cytokines.⁵

Anti-Inflammatory Polyphenols for Brain Health

Research has shown us that dietary polyphenols are linked with the prevention of disease, helping to support brain health, reduce neuroinflammation and improve overall health.^17,18 Polyphenols have been shown to have the ability to cross into the brain and exert anti-inflammatory, antioxidant and neuroprotective properties.¹⁷

What are Polyphenols?

Polyphenols are plant-based compounds naturally found in fruits, vegetables, herbs, spices, tea, dark chocolate, and red wine.¹⁹

The four main categories are:

Flavonoids: these are found in a variety of colourful fruits, vegetables, tea, and red wine.

Phenolic acids: these are found in the seeds, skins, and leaves of fruits and vegetables.

Lignans: these are found in whole grains, nuts, and seeds.

Stilbenes: these are abundant in peanuts, grapes, and berries.

Foods High in Polyphenols

Berries: particularly elderberries, blueberries, blackberries, raspberries, strawberries, black olives, pomegranate, apples, grapes, cherries, and plums.

Cocoa powder and dark chocolate: heating and processing can reduce the polyphenol content, aim for at least 80% dark chocolate.

Nuts: particularly chestnuts, hazelnuts, pecans, walnuts, and almonds.

Seeds: particularly chia seeds and flaxseeds

A variety of colours of vegetables: particularly artichoke, red onion, fresh spinach, broccoli, asparagus, shallots, carrots

Herbs and spices: garlic, turmeric, cinnamon, ginger, cloves, basil, rosemary, sage, and thyme.

Coffee and green tea

A diet that is abundant in antioxidant rich polyphenols helps to reduce the consequences of aging, reduce neuroinflammation and improve your overall health.^18,20

References

1. DiSabato DJ, Quan N, Godbout JP. Neuroinflammation: the devil is in the details. J Neurochem. 2016 Oct 1;139:136–53.
2. Liu YZ, Wang YX, Jiang CL. Inflammation: the common pathway of stress-related diseases. Frontiers in human neuroscience. 2017;11:316.
3. Peters R. Ageing and the brain. Postgraduate medical journal. 2006 Feb 1;82(964):84-8.
4. Graff BJ, Payne SJ, El-Bouri WK. The Ageing Brain: Investigating the Role of Age in Changes to the Human Cerebral Microvasculature With an in silico Model. Frontiers in Aging Neuroscience. 2021 Aug 5;13:632521.
5. Munhoz CD, Garcia-Bueno B, Madrigal JL, Lepsch LB, Scavone C, Leza JC. Stress-induced neuroinflammation: mechanisms and new pharmacological targets. Brazilian Journal of Medical and Biological Research. 2008;41:1037-46.
6. Yaffe K, Kanaya A, Lindquist K, Simonsick EM, Harris T, Shorr RI, Tylavsky FA, Newman AB. The metabolic syndrome, inflammation, and risk of cognitive decline. Jama. 2004 Nov 10;292(18):2237-42.
7. Van Dyken P, Lacoste B. Impact of metabolic syndrome on neuroinflammation and the blood–brain barrier. Frontiers in neuroscience. 2018 Dec 11;12:930.  
8. Lawrence BP. Environmental toxins as modulators of antiviral immune responses. Viral immunology. 2007 Jun 1;20(2):231-42.  
9. Yang SN, Hsieh CC, Kuo HF, Lee MS, Huang MY, Kuo CH, Hung CH. The effects of environmental toxins on allergic inflammation. Allergy, asthma & immunology research. 2014 Nov 1;6(6):478-84.
10. Aloizou AM, Siokas V, Vogiatzi C, Peristeri E, Docea AO, Petrakis D, Provatas A, Folia V, Chalkia C, Vinceti M, Wilks M. Pesticides, cognitive functions and dementia: A review. Toxicology letters. 2020 Jun 15;326:31-51.
11. Klein RS, Garber C, Funk KE, Salimi H, Soung A, Kanmogne M, Manivasagam S, Agner S, Cain M. Neuroinflammation during RNA viral infections. Annual review of immunology. 2019 Apr 26;37:73-95.
12. McCullagh CD, Craig D, McIlroy SP, Passmore AP. Risk factors for dementia. Advances in psychiatric treatment. 2001 Jan;7(1):24-31.
13. Conway SG, Roizenblatt SS, Palombini L, Castro LD, Bittencourt LR, Silva RS, Tufik S. Effect of smoking habits on sleep. Brazilian journal of medical and biological research. 2008;41:722-7.
14. Whitman IR, Agarwal V, Nah G, Dukes JW, Vittinghoff E, Dewland TA, Marcus GM. Alcohol abuse and cardiac disease. Journal of the American College of Cardiology. 2017 Jan 3;69(1):13-24.
15. Yaffe K, Kanaya A, Lindquist K, Simonsick EM, Harris T, Shorr RI, Tylavsky FA, Newman AB. The metabolic syndrome, inflammation, and risk of cognitive decline. Jama. 2004 Nov 10;292(18):2237-42.
16. Hirotsu C, Tufik S, Andersen ML. Interactions between sleep, stress, and metabolism: From physiological to pathological conditions. Sleep Science. 2015 Nov 1;8(3):143-52.
17. Castelli V, Grassi D, Bocale R, d'Angelo M, Antonosante A, Cimini A, Ferri C, Desideri G. Diet and brain health: which role for polyphenols?. Current pharmaceutical design. 2018 Jan 1;24(2):227-38.
18. Shabbir U, Tyagi A, Elahi F, Aloo SO, Oh DH. The potential role of polyphenols in oxidative stress and inflammation induced by gut microbiota in alzheimer’s disease. Antioxidants. 2021 Aug 27;10(9):1370.
19. Brat P, Georgé S, Bellamy A, Chaffaut LD, Scalbert A, Mennen L, Arnault N, Amiot MJ. Daily polyphenol intake in France from fruit and vegetables. The Journal of nutrition. 2006 Sep 1;136(9):2368-73.
20. Singh A, Yau YF, Leung KS, El-Nezami H, Lee JC. Interaction of polyphenols as antioxidant and anti-inflammatory compounds in brain–liver–gut axis. Antioxidants. 2020 Jul 26;9(8):669.