Why your mouthwash may be undermining the vegetables you eat
The oral microbiome converts dietary nitrate into nitric oxide — a molecule that regulates blood pressure, insulin sensitivity and vascular health. Antibacterial mouthwash kills the bacteria that make this conversion possible.
science
When you eat leafy greens, beetroot or celery, you consume dietary nitrate. In your mouth, bacteria living on the surface of your tongue — particularly species like Neisseria, Rothia and Veillonella — convert that nitrate into nitrite. When you swallow and the nitrite reaches the acidic environment of the stomach, it is converted into nitric oxide. This pathway, known as the nitrate-nitrite-nitric oxide pathway, is one of the primary ways your body regulates blood pressure, vascular tone and insulin sensitivity.
Nitric oxide is a signalling molecule produced by the endothelium — the thin layer of cells lining your blood vessels. It relaxes the vessel wall, reducing resistance and lowering blood pressure. It improves the sensitivity of cells to insulin. It modulates inflammation at the vascular level. Your body produces some nitric oxide via an enzyme called endothelial nitric oxide synthase, but the dietary pathway — through oral bacteria — provides a meaningful additional source that operates independently of this enzyme.
Human cells lack the enzyme nitrate reductase entirely — meaning the conversion of dietary nitrate to nitrite cannot happen without oral bacteria. If those bacteria are eliminated, the nitrate you consume from vegetables passes through the body without contributing to nitric oxide production
A 2025 cross-sectional study found that regular over-the-counter mouthwash use was associated with lower salivary and plasma nitrite levels and higher markers of inflammation and endothelial dysfunction, including IL-6, TNF-α and sICAM-1
A 2024 Nature Scientific Reports study found that antibacterial mouthwash in mice altered the gut microbiome, reduced absorption of dietary triglycerides and and lowered plasma insulin levels — suggesting the oral microbiome's influence on nutrient absorption extends well beyond the mouth
When chlorhexidine mouthwash was used in fasting individuals, plasma nitrite levels dropped and blood pressure measurably increased within days — a direct demonstration of the oral bacteria's contribution to cardiovascular regulation
Over-the-counter mouthwash use has been associated in epidemiological studies with increased risk of diabetes and pre-diabetes, consistent with the hypothesis that chronically reduced nitric oxide availability impairs insulin sensitivity over time
The bacteria most responsible for nitrate reduction live on the posterior dorsal surface of the tongue — a region that standard toothbrushing does not reach. Antiseptic mouthwashes containing chlorhexidine or cetylpyridinium chloride are effective at reducing these bacteria indiscriminately, along with the pathogens they are intended to target. The clinical evidence for mouthwash preventing dental caries or periodontitis is surprisingly weak; the evidence for its disruption of the nitrate pathway is growing.
This does not mean oral hygiene is unimportant — gum disease itself impairs nitrate reduction capacity, as the periodontal bacteria that cause it crowd out the beneficial nitrate-reducing species. The nuance is that brushing, flossing and regular dental care support the oral microbiome; daily antibacterial mouthwash disrupts it. If you eat vegetables for their nutritional value, the bacteria in your mouth are part of that nutritional equation.