Your mouth is the front door to your body: the oral microbiome, bleeding gums and what they say about the rest of you

What the oral microbiome is

Researchers have identified around 700 species of bacteria that commonly live in the human mouth, spread across distinct habitats: the tongue, the cheeks, the surfaces of teeth and the pockets between teeth and gums (Dewhirst et al., 2010). In health these communities are balanced, and many of them do useful work — helping to protect against harmful species and, as we'll see, contributing to blood pressure regulation.

Problems arise when the balance tips. Plaque that is left undisturbed matures into a more inflammatory community, and the gums respond with swelling and bleeding. That early stage, gingivitis, is reversible. If it continues for long enough, it can progress to periodontitis, where the tissues and bone supporting the teeth are damaged — and that damage is much harder to undo.

Bleeding gums are inflammation you can see. Gingivitis is reversible, and it is worth taking seriously early.

What throws it off

• Frequent sugar: it isn't only the amount but how often. Grazing on sugary foods and drinks feeds acid-producing bacteria all day. Systematic review evidence links higher sugar intake with more tooth decay (Moynihan & Kelly, 2014).
• Plaque left between teeth, where a toothbrush can't reach.
• A dry mouth from mouth breathing, dehydration or medications. Saliva is your mouth's natural rinse and remineralising fluid.
• Smoking and vaping, which change the microbial community and can mask bleeding.
• Uncontrolled blood sugar. Periodontitis and diabetes affect each other in both directions (Preshaw et al., 2012).
• Hormonal change: puberty, the menstrual cycle, pregnancy and menopause can all affect the gums (Mascarenhas et al., 2003).
• Overusing strong antiseptic mouthwash when you don't need it, which can wipe out helpful species along with harmful ones.

Your mouth, your gut and your blood vessels

The mouth and gut are one continuous system. A study tracking bacterial strains found that oral microbes regularly travel to and settle in the gut (Schmidt et al., 2019). In mouse studies, certain oral bacteria that colonised the gut triggered inflammatory immune responses (Atarashi et al., 2017), and gum inflammation worsened gut inflammation through oral bacteria and immune cells moving between the two (Kitamoto et al., 2020). These are animal findings, so they don't prove the same happens in people, but they make the mouth–gut link biologically plausible.

There is also a well-established association between gum disease and cardiovascular disease. A European consensus report concluded that periodontitis is associated with higher cardiovascular risk and that treating it improves some markers of inflammation and blood vessel function, while noting that this doesn't prove gum disease causes heart disease (Sanz et al., 2020).

One of my favourite examples of a helpful oral microbe involves leafy greens and beetroot. Some mouth bacteria convert dietary nitrate into nitrite, which the body can turn into nitric oxide, a molecule that relaxes blood vessels. In studies, using antiseptic mouthwash reduced this conversion and raised blood pressure slightly (Kapil et al., 2013; Bondonno et al., 2015). Your mouth bacteria are part of your cardiovascular system.

The hormone connection

Gum tissue has receptors for oestrogen and progesterone, and changes in these hormones can alter blood flow and inflammatory responses in the gums (Mascarenhas et al., 2003). That is why so many women notice tender or bleeding gums before a period or during pregnancy. Pregnancy gingivitis is common, and periodontal disease in pregnancy has been studied in relation to pregnancy outcomes, although whether treating it improves those outcomes is still debated (Raju & Berens, 2021).

In practice, this means life stages with big hormonal shifts — pregnancy, perimenopause and menopause — are good times to be especially consistent with gum care and to keep up dental visits.

Remineralisation: what your teeth need

Tooth enamel is constantly losing and regaining minerals. When acid levels rise after eating, minerals are drawn out; when the mouth recovers, saliva supplies calcium and phosphate to put them back. Remineralisation is real, but it works on early weakening, not established cavities.

• Fluoride toothpaste has strong evidence for preventing decay (Marinho et al., 2003).
• Hydroxyapatite toothpaste — made from the same mineral as enamel — performed as well as fluoride toothpaste in an 18-month trial in adults (Paszynska et al., 2023). It is a reasonable option for people who prefer to avoid fluoride, though the evidence base is smaller. Talk to your dentist about which suits you.
• Calcium and phosphate from food: full-fat organic dairy (or A2, sheep or goat options), sardines and tinned salmon with bones, tahini, almonds, leafy greens, eggs and legumes.
• Vitamin D supports calcium handling. A review of older trials suggested vitamin D was associated with fewer cavities in children, but most trials were old and of low quality (Hujoel, 2013).
• Vitamin C matters for gum tissue. A meta-analysis linked lower vitamin C status with a greater tendency for gum bleeding (Hujoel et al., 2021). Peppers, citrus, kiwi, berries and broccoli are excellent sources.
• Vitamin K2 is often mentioned for teeth. The idea is plausible, but good human evidence for dental benefits is limited.

A simple daily routine, not fifteen new products

Here is the routine I actually recommend. It is deliberately short.

• Brush twice a day for two minutes with a fluoride or hydroxyapatite toothpaste. Spit, but don't rinse straight away, so the active ingredient stays on your teeth.
• Clean between your teeth once a day with interdental brushes or floss. A Cochrane review found interdental cleaning alongside brushing may reduce gum inflammation, with interdental brushes looking particularly useful, although the evidence certainty is low (Worthington et al., 2019).
• Keep sweet foods and drinks to mealtimes rather than spreading them through the day, and drink water after meals.
• Eat crunchy vegetables, leafy greens and some beetroot through the week to support both your gums and your nitrate-reducing bacteria.
• Breathe through your nose where you can, and talk to your dentist or GP if you wake with a dry mouth.
• Skip daily antiseptic mouthwash unless your dentist has recommended it for a specific reason.
• See your dentist and hygienist regularly, and go sooner if bleeding persists for more than a couple of weeks of good cleaning.

If your gums still bleed after two to three weeks of consistent brushing and interdental cleaning, book a dental check rather than adding another product.

What about oil pulling, xylitol and tongue scraping?

I get asked about these a lot. Xylitol may help reduce decay, but a Cochrane review rated the evidence as low quality (Riley et al., 2015). Oil pulling and tongue scraping are popular and generally harmless, but the evidence is limited and they shouldn't replace brushing and interdental cleaning. If you enjoy them, fine — just don't let them crowd out the basics that work.

Before you act on any of this

This article is for education and general information only. It isn't medical advice, it can't diagnose or treat any condition, and it doesn't replace a consultation with your own doctor or a qualified practitioner who knows your history. Please don't start, stop or change any medication, hormone or supplement because of something you've read here — take your questions to the person responsible for your care.

Persistent bleeding, loose teeth, receding gums or bad breath that doesn't improve need a dental assessment.

References

• Atarashi, K., Suda, W., Luo, C., et al. (2017). Ectopic colonization of oral bacteria in the intestine drives TH1 cell induction and inflammation. Science, 358(6361), 359–365.
• Bondonno, C.P., Liu, A.H., Croft, K.D., et al. (2015). Antibacterial mouthwash blunts oral nitrate reduction and increases blood pressure in treated hypertensive men and women. American Journal of Hypertension, 28(5), 572–575.
• Dewhirst, F.E., Chen, T., Izard, J., et al. (2010). The human oral microbiome. Journal of Bacteriology, 192(19), 5002–5017.
• Hujoel, P.P. (2013). Vitamin D and dental caries in controlled clinical trials: systematic review and meta-analysis. Nutrition Reviews, 71(2), 88–97.
• Hujoel, P.P., Kato, T., Hujoel, I.A., & Hujoel, M.L.A. (2021). Bleeding tendency and ascorbic acid requirements: systematic review and meta-analysis of clinical trials. Nutrition Reviews, 79(9), 964–975.
• Kapil, V., Haydar, S.M.A., Pearl, V., et al. (2013). Physiological role for nitrate-reducing oral bacteria in blood pressure control. Free Radical Biology and Medicine, 55, 93–100.
• Kitamoto, S., Nagao-Kitamoto, H., Jiao, Y., et al. (2020). The intermucosal connection between the mouth and gut in commensal pathobiont-driven colitis. Cell, 182(2), 447–462.
• Marinho, V.C.C., Higgins, J.P.T., Logan, S., & Sheiham, A. (2003). Fluoride toothpastes for preventing dental caries in children and adolescents. Cochrane Database of Systematic Reviews, (1), CD002278.
• Mascarenhas, P., Gapski, R., Al-Shammari, K., & Wang, H.L. (2003). Influence of sex hormones on the periodontium. Journal of Clinical Periodontology, 30(8), 671–681.
• Moynihan, P.J., & Kelly, S.A.M. (2014). Effect on caries of restricting sugars intake: systematic review to inform WHO guidelines. Journal of Dental Research, 93(1), 8–18.
• Paszynska, E., Pawinska, M., Enax, J., et al. (2023). Caries-preventing effect of a hydroxyapatite-toothpaste in adults: an 18-month double-blinded randomized clinical trial. Frontiers in Public Health, 11, 1199728.
• Preshaw, P.M., Alba, A.L., Herrera, D., et al. (2012). Periodontitis and diabetes: a two-way relationship. Diabetologia, 55(1), 21–31.
• Raju, K., & Berens, L. (2021). Periodontology and pregnancy: an overview of biomedical and epidemiological evidence. Periodontology 2000, 87(1), 132–142.
• Riley, P., Moore, D., Ahmed, F., Sharif, M.O., & Worthington, H.V. (2015). Xylitol-containing products for preventing dental caries in children and adults. Cochrane Database of Systematic Reviews, (3), CD010743.
• Sanz, M., Marco del Castillo, A., Jepsen, S., et al. (2020). Periodontitis and cardiovascular diseases: consensus report. Journal of Clinical Periodontology, 47(3), 268–288.
• Schmidt, T.S.B., Hayward, M.R., Coelho, L.P., et al. (2019). Extensive transmission of microbes along the gastrointestinal tract. eLife, 8, e42693.
• Worthington, H.V., MacDonald, L., Poklepovic Pericic, T., et al. (2019). Home use of interdental cleaning devices, in addition to toothbrushing, for preventing and controlling periodontal diseases and dental caries. Cochrane Database of Systematic Reviews, (4), CD012018.