The Bacteria in Your Mouth May Help Determine Whether Vegetables Lower Your Blood Pressure

Researchers at the University of Exeter have published what they describe as the largest study of its kind examining how dietary nitrate — the compound found in beetroot, spinach, and other vegetables — affects mouth bacteria, nitric oxide biology, and blood vessel function across two age groups. The study, which appeared in the journal Free Radical Biology and Medicine, recruited 39 adults under age 30 and 36 adults in their 60s and 70s. Participants spent two weeks drinking a concentrated nitrate-rich beetroot juice shot twice daily, and two separate weeks drinking an identical placebo with the nitrate removed, with a washout period between each phase.

The key finding was that blood pressure fell in the older group during the nitrate phase, while the younger group saw no comparable drop — even though both groups experienced changes in their oral microbiome. The researchers traced the effect to specific bacterial shifts in the older participants' mouths: levels of a potentially harmful bacterium called Prevotella declined, while beneficial Neisseria bacteria increased. This matters because certain mouth bacteria are responsible for converting dietary nitrate into nitrite, which the body then uses to produce nitric oxide — a molecule that signals blood vessels to relax. Without those bacteria doing their job, the nitrate from food largely passes through without delivering its cardiovascular benefit.

The study also noted a relevant finding about antiseptic mouthwash. A companion pilot study cited in the Exeter research found that chlorhexidine, the active agent in many prescription-strength rinses, disrupted this same nitrate-processing pathway and reduced the body's nitric oxide production. This adds to a growing body of evidence suggesting that routine use of broad-spectrum antiseptic rinses may inadvertently suppress bacteria the body relies on for more than just oral hygiene.

The researchers were careful to note that beetroot juice is not a substitute for blood pressure medication, and that larger trials are needed to understand why individuals respond differently based on age, sex, health status, and the specific bacteria present in their mouths at baseline. For patients interested in supporting cardiovascular health through diet, the Exeter team pointed out that beetroot is not the only option — spinach, arugula, fennel, celery, and kale are all meaningful sources of dietary nitrate, and the underlying pathway they support runs directly through the mouth.