The results, published in Free Radical Biology and Medicine, may have health implications due to the important role of nitric oxide and its production from dietary nitrates.
“Switching from a sedentary to an active lifestyle alters both the microbiome of the tongue and the bioavailability of nitrate and nitrite, with potential implications for oral and systemic health,” wrote researchers from the Sport and Physical Activity Research Institute, University of the West of Scotland, and other European institutions.
Nitric oxide
Nitric oxide (NO) is a gas produced by the body and from nitrates in the diet. As a signaling molecule, it relaxes blood vessels, increasing blood supply and lowering blood pressure. It is linked to improved cardiovascular health and exercise performance.
However, its signaling role is central to numerous other physiological processes, including inflammation, oxidative stress, mucus production and neurotransmission. Research suggests that NO availability decreases with aging, especially in sedentary individuals.
The body can produce NO endogenously by enzymatic conversion of the amino acid l-arginine by nitric oxide synthase (NOS). NOS is upregulated during exercise.
NO is also produced when oral bacteria help to convert nitrates in foods such as leafy green vegetables and beetroot to nitrites. Once formed, the nitrites are swallowed and converted to NO in the stomach’s acidic environment.
The current study is reportedly the first to investigate HIITs effects on the oral microbiome and nitrite production.
Study details
Eleven untrained males completed HIIT training three times a week (16 to 36 minutes per session) for eight weeks, followed by a 12-week detraining period during which they returned to their usual activity.
Researchers collected blood, saliva and tongue swab samples at baseline, after training and after detraining and took a muscle biopsy under local anesthesia. They used RNA sequencing and liquid chromatography to analyze nitrate and nitrite levels and bacterial species.
They reported that nine bacterial species increased in abundance following HIIT training. Five species were nitrite-producing bacteria, including Rothia mucilaginosa and Streptococcus salivarius.
“High-intensity exercise training increased the abundance of several nitrite-producing bacteria and altered nitrate and nitrite levels in saliva, plasma and muscle,” they reported.
Following detraining, several nitrite-producing bacteria remained elevated above baseline levels. However, when regular activity resumed, nitrate and nitrite bioavailability in blood, saliva and muscle appeared to return to baseline levels.
Hypothesizing the mechanisms involved, the researchers noted that exercise-induced NO synthesis in endothelial and muscle cells rapidly oxidizes to nitrate and nitrite, with “nitrate being a more stable and abundant molecule in plasma.”
Some of this nitrate may be absorbed by the salivary glands “and excreted in the oral cavity with saliva, where it can stimulate the growth and activity of nitrite-producing bacteria, consequently increasing nitrite bioavailability.”
They noted that lactate synthesis may be another mechanism by which exercise can modify the oral microbiome.
Source: Free Radical Biology and Medicine, 2025, ISSN 0891-5849. doi: 10.1016/j.freeradbiomed.2025.02.006. “Eight Weeks of High-Intensity Interval Training Alters the Tongue Microbiome and Impacts Nitrate and Nitrite Levels in Previously Sedentary Men”. Authors: A. Simpson et al.