The mouth is a hub of activity, housing around 50–100 billion bacteria from 200 different bacterial species. The role of these resident bacteria in the mouth, also known as the oral microbiome, is an emerging area of research. Alterations in the oral microbiome may occur as a result of factors including consuming high amounts of sugar, smoking tobacco and experiencing chronic stress. Drinking large amounts of alcohol can also negatively impact the oral microbiome. Disruptions to the oral microbiome can lead to gut dysbiosis, which has been associated with increased permeability of the Blood Brain Barrier (BBB). 

Findings to date suggest that the oral microbiome, via interactions with the gut and brain (a network called the oral-gut-brain axis), may be a key consideration for brain health, and multiple associated conditions. This post will focus on three key areas where there is present research: autism, Down’s syndrome, and Alzheimer’s disease. 

Autism

Individuals with autism have been indicated to have alterations in their oral microbiome, as well as gut dysbiosis and related disruptions to the gut-brain axis. A study investigating the oral microbiome indicated that children with autism have a higher incidence of gastrointestinal disturbance and food allergies. Moreover, children with autism were observed to have a disruption to the ratio of Firmicutes: Bacteroidetes bacteria, in favour of Firmicutes. Balance of the Firmicutes: Bacteroidetes ratio is key for integrity of the gut, and disruptions to this ratio are indicative of gut dysbiosis.  

Moreover, two specific groups of bacteria, Brucella and Enterococcus faecalis were observed to be elevated in autistic children, whilst Flavobacterium sp. levels were demonstrated to be decreased. Research has suggested that individuals with autism have a higher risk of developing Alzheimer’s disease earlier in life. One potential mechanism for this could be due to alterations to the Firmicutes: Bacterodetes ratio.

Firmicutes and Bacteroidetes both utilise amyloids in the gut as structural material. Recognition of amyloids may become impaired by increased synthesis of inflammatory T cells by the innate immune system, as the result of intestinal permeability. Translocation of amyloids across the BBB has been hypothesised to be associated with enhanced Aβ deposit in the brain, although this requires further research.

Down’s Syndrome

Individuals with Down’s syndrome have been demonstrated to be more susceptible to periodontitis, or gum disease. One potential explanation for these findings could be due to alterations in oral microbiome composition. One study observed that individuals with Down’s syndrome have higher levels of Streptococcus mutans in their saliva. A further study observed increased levels of the pathogenic bacterial strains Aggregatibacter actinomycetemcomitans and Porphyromonas gingivalis.  Individuals with Down’s syndrome have an increased risk of developing Alzheimer’s disease later in life, with 50% of individuals >60 years of age meeting diagnostic criteria for dementia. One hypothesised mechanism for this is because of altered expression of inflammation and immune system modulating genes in periodontitis.

Alzheimer’s Disease

Individuals with Alzheimer’s disease have been observed to have higher levels of the oral bacteria, Treponema, in the brain. Moreover, disruptions to the oral-gut-brain axis has been associated with increased accumulation of beta amyloid and Tau, two key markers of Alzheimer’s disease.

Supporting the Oral-Gut-Brain Axis 

Supporting the oral-gut-brain axis is an area of research that is undeveloped, however, it seems logical that many of the measures employed for supporting gut and brain health would also be salient. 

Increase Fibre & Polyphenols

Consuming a wide array of colourful vegetables, fruits, herbs and spices is a great way of increasing prebiotic fibres, which help to support gut health via increasing production of SCFAs (short chain fatty acids), and polyphenols, plant compounds that have antioxidant properties and have been demonstrated to support the oral-gut-brain axis. 

Increase Omega-3 Fats

Omega-3 fats exert anti-inflammatory effects in the body, whilst increasing microbiome diversity via balancing the Firmicutes: Bacteroidetes ratio, which is essential for gut health and gut barrier integrity. Additionally, increased levels of omega-3 have been associated with reduced incidence of periodontitis. Ways to increase omega-3 include increasing consumption of oily fish such as salmon, mackerel and sardines, and also flaxseeds, walnuts and algae. 

Increase Fermented, Probiotic Foods

Probiotics have been associated with improved oral health due to decreased presence of pathogenic bacteria in the mouth. Examples of probiotic foods include fermented foods such as kimchi, kombucha, kefir, sauerkraut and sourdough bread.

Stress is a human adaptive response involving complex, yet fascinating physiological and psychological mechanisms. 

Stress has been designed for our daily survival as species, however, when stress becomes the only response we can lean on to live our lives we may find ourselves trapped in a loop with detrimental effects to our overall health and wellbeing.

Exposure to intense, repetitive and prolonged stress (chronic stress) tells our bodies and minds to continue to respond with stress, even when the stressful event is no longer present. Our bodies will not only adapt to cope with higher levels of stress, but will also continue to release hormones (cortisol and adrenaline) that keep this adaptive physical response or continuous loop going. 

This stress mind-body loop can feed an endless list of physical and mental health issues such as Alzheimer’s disease, Type 2 diabetes, insomnia, IBS, depression and anxiety, but it can also impact our nutritional status, i.e. the essential vitamins and minerals that our bodies need to survive and thrive.

Stress can lead to prolonged release of the stress hormone cortisol, impacting the ability of our brains and adrenal glands to regulate it. In turn, excessive cortisol creates inflammation and weakens our immune system.

Nonetheless, stress responses are a key part of our body’s ability to self-regulate and bring itself to a state of homeostasis. Think about stress as a continuum, varying from positive stress-resilient responses to negative ill-health stress responses. As we navigate through this continuum day by day, nutrition and lifestyle can become one of our best allies in helping to minimise the negative effects of this loop, if not stop it completely.

A diet rich in omega-3 fats, vitamin E, magnesium, folic acid and vitamin B6 has been associated with positive benefits with regards to stress resilience. Omega-3 fats can be found in oily fish, flaxseeds and walnuts; vitamin E in olive oil, olives, avocados, nuts and seeds; magnesium in almonds, bananas and dark green leafy vegetables such as kale and broccoli; folic acid in organ meats, spinach and beans; and B6 in chicken, salmon, chickpeas and sunflower seeds. These nutrients can help by regulating our stress response, balancing our hormones, strengthening our immune system and protecting our brain function and mental wellbeing.

Eating processed and refined foods with a higher number of calories and lower nutrient content (e.g. sugar, alcohol, saturated and trans-fats), can make us feel increasingly tired, irritable, anxious and lacking attention and focus. These foods can cause our blood sugar levels to rise quickly then drop suddenly like a rollercoaster ride. A simple change to more nutrient-dense meals and foods, i.e. foods with a high level of essential vitamins and minerals and other nutrients, such as protein, fibre and complex carbohydrates can be very supportive for the body during times of stress.

A lifestyle that includes regular exercise, restorative sleep and rest, emotional support, positive social interactions and relationships, and plenty of laughter, fun and creativity can also help boost our resilience to stress and adversities and support a shift whereby stress is no longer perceived as a permanent threat but as an adaptive bio-psychological response.

With thanks to our volunteer, Catia Soares, for this article. Catia is a Psychologist and Nutritional Therapist with more than 11 years experience in the field.