Brain health - it's worth mouthing off about

Increasingly, we are understanding that brain health is not just about the brain; the whole body is involved. It was the intuitive truth of this body-mind connection that attracted me to researching the microbiome in the first place.

The health of the gut and its microbiome, and their role in mental and brain health gets a lot of air-time here and in the microbiome world at large.

But what about that microbial haven right near the brain: the mouth?

The mouth contains a number of different microbial communities on the tongue, plaque, gums and so on.

All up, your mouth provides a home for over 700 species of microbes, which play a part in keeping teeth and gums healthy.

An overgrowth of certain species like Porphrymonous gingivalis can herald the start of gingivitis (gum disease), and Streptococcus mutans has been shown to predict caries in children.

But back to the brain. Poor oral health is known to co-occur with anxiety and depression, probably in a bi-directional way. Experiencing mental health difficulties may reasonably reduce one's interest in flossing. But also, it seems that oral disease is a risk factor for later mental health disorders. A recent study has shown differences in the oral microbiomes of young people with depression or anxiety, which may help to explain why oral health matters.

And when it comes to risk of Alzheimer's disease and dementia, the evidence for an oral health link is even more compelling.

In identical twins (who therefore share the same genes), tooth loss before the age of 35 was one of the few modifiable factors predicting risk of subsequent onset of dementia three decades later. In co-habiting nuns (who therefore share the same environment and many aspects of lifestyle), those with the fewest teeth (1 to 9 teeth) had the highest risk of dementia. Both studies controlled for other factors known to impact dementia risk, such as age, education and medical conditions.

So oral health is clearly important for the brain. But is this due to the oral microbiome, or something else about having few teeth or dental disease?

Next time I'll present the case for oral microbes, and you can be the jury as to whether they are guilty as charged.