High blood pressure (hypertension) is a major risk factor for cardiovascular disease. One important contributing factor to high blood pressure is reduced availability of nitric oxide (NO). Therefore, NO is an important molecule in maintaining healthy blood vessel function.

Dietary nitrate, found in leafy greens, can serve as an alternative source of nitric oxide in the body. After ingestion, nitrate is converted to nitrite by bacteria residing in the oral cavity. Nitrite can subsequently be converted to NO when swallowed. Therefore, this nitrate-nitrite-nitric oxide pathway is dependent on oral bacteria.

This study aims to assess whether rinsing the mouth with a nitrate-rich mouth rinse influences blood pressure in healthy adults. Also, concentrations of nitrate and nitrite in plasma and saliva will be measured following the nitrate-mouth rinse exposure.

This study investigates the potential acute blood pressure lowering effects of a simple nitrate-rich mouth rinse and drink, while also monitoring their effects on oral nitrite production capacity (NPC), plasma and salivary nitrate and nitrite levels, oral pH levels and the oral microbiology.

The study is a short-term, double-blind, randomized, placebo-controlled, crossover trial.

Participants will receive interventions and donate samples at four separate sessions. At session (i), baseline measurements are taken prior to intervention, and samples are subsequently taken (as described under outcome measures). At session (i) and (ii), the participants will rinse the oral cavity with a nitrate-rich fluid (or placebo). Similarly for sessions (iii) and (iv), the participants will drink the same fluid (or placebo). When donating samples, the participants will be in fasting condition. In total there will be four sessions per participant with wash-out periods in-between.

To elucidate the short-term effects of the above-described interventions, sampling will be performed in the clinic at multiple time points during the first 2 hours after each intervention, as well as at 24 hours. Participants will also monitor their blood pressure at home at four different time points for all four interventions. No sampling or measurements will be performed during night-time.

For both the intervention and the placebo, potassium (K) salts are used (KNO3 and KCl). For chairside measurement of NPC in oral samples, the rapid Griess assay (RGA) will be used. Blood pressure will be measured at the study facilities as clinic blood pressure and orthostatic blood pressure (CBP and OBP, respectively) using a clinically validated blood pressure monitor. The same device will be used by the participants for home blood pressure measurements (HBP). Saliva pH will be measured using pH-sticks or a pH-meter. Plasma and saliva nitrate- and nitrite levels are analyzed using commercial laboratory kits. Salivary secretion rate (SCR) is recorded during saliva donation, and measured as volume per unit time. Microbiological effects will be analyzed with appropriate methods in the laboratory.

Inclusion Criteria:

• ≥18 years of age; and
• clinic blood pressure <140/<90 mmHg.

Exclusion criteria:

• hypertension;
• systemic medication (other than the oral contraceptive pill);
• antibiotic treatment within the last 3 months;
• active smoking status and BMI > 30;
• prior gastric by-pass surgery;
• self-reported use of antiseptic mouthwash or toothpaste;
• self-reported use of tongue scrapes; and
• active periodontal disease or caries that needs treatment.