For the first time, researchers at King's College London have discovered a link between chewing sugary gum after consuming vegetables high in nitrate, such as beetroot, spinach and kale, on lowering blood pressure.
Nitrate is absorbed by vegetables from the soil, but it needs to be converted into nitrite by bacteria in the mouth before it can be used by the body. Nitrite has wide-ranging effects, including the relaxation and widening of blood vessels, which enables blood to flow more easily, lowering blood pressure.
With these cardiovascular benefits limited by the bacteria in the mouth converting nitrate into nitrite which can be used by the body, scientists are investigating how this process might be enhanced. A little-explored theory is that increasing the acidity in saliva could increase this chemical reaction.
To test this theory, researchers investigated whether chewing sugar-containing gum, which is acidic and lowers the pH in the mouth, increases nitrite production.
Dr Andrew Webb, Clinical Senior Lecturer in the School of Cardiovascular & Metabolic Medicine & Sciences, King's College London, said: "Whether and how the acidity of the saliva in the mouth impacts the conversion of the inactive nitrate, to the more active nitrite, is a fundamental question, as it impacts a range of important physiological functions including blood pressure. However, this process has not been studied much.
"While most research suggests that increasing acidity inhibits the conversion of nitrate, this has never been investigated in the whole body, over several hours.
"Incidentally, we previously found that combining grapefruit juice with beetroot juice decreased the acidity of the saliva and inhibited the conversion of nitrate to nitrite in the saliva. So, we wanted to formally test whether doing the opposite – increasing the acidity of the saliva – would enhance the conversion of nitrate to nitrite."
Healthy volunteers were randomly allocated to chew sugar-containing (Hubba Bubba® bubble) gum, or sugar-free (Wrigley's Extra®) chewing gum, for three to six hours after drinking a shot of beetroot juice. Blood and saliva samples were analysed throughout the study, alongside blood pressure measurements. The volunteers returned at least a week later to repeat the experiment but chewing the other gum.
When volunteers chewed Hubba Bubba, the acidity of the saliva increased (measured by a 1.4 decrease in pH) compared to chewing the sugar-free gum. The participants also had a 45% higher amount of nitrite in the mouth and 25% higher level of nitrite around the body, compared to when they chewed sugar-free gum.
Chewing sugary gum also significantly decreased systolic blood pressure (when the heart pushes blood out) and diastolic blood pressure (when the heart relaxes between beats) by almost 3/2 mmHg, compared to sugar-free gum.
While the researchers stress that chewing sugary gum is not a therapeutic approach for people trying to manage their blood pressure, the finding could have implications for sports people already harnessing the effects of beetroot to improve their athletic performance.
Dr Webb added: "The effects were only short-term, lasting several hours, and long-term use of sugar-containing products would not be recommended for dental health. Nonetheless, the classic culinary tradition of following a starter and a main course, especially if they contain nitrate-rich salad leaves and vegetables, with a sweet dessert – which could be fruit – may temporarily increase blood pressure-lowering and exercise enhancement.
"We also suggest that sugary chewing gum will have a greater effect compared to drinking sugary drinks, as it stays in the mouth for a longer period of time."
Co-author Dr Charlotte Mills, University of Reading, added: "The bacteria that live in our mouths play a critical role in converting nitrate from foods such as beetroot into beneficial compounds that help relax blood vessels and lower blood pressure. Our findings suggest that the presence of sugar may create a more favourable environment for this process.
"We are certainly not suggesting that people should start chewing sugary gum regularly. Frequent sugar consumption is harmful for dental health and is also detrimental to cardiometabolic health when consumed in excess. Instead, our findings provide a proof of concept that we may be able to improve how the body processes dietary nitrate, and future research should focus on developing tooth-friendly, metabolically sound approaches that achieve the same effect.
"The challenge now is to identify alternative strategies that are both effective and appropriate for long-term use.
"Because dietary nitrate is already a recognised sports supplement, there is potential to optimise how athletes use it. If we can enhance nitrate conversion, we may be able to improve the physiological benefits that athletes obtain from nitrate-rich foods.
"We found that something as simple as the type of chewing gum used alongside beetroot juice can influence how effectively the body converts dietary nitrate into compounds that help lower blood pressure."
For the next steps, the scientists propose conducting a larger study focused on sports people, to further investigate the relationship between sugary chewing gum, blood pressure and athletic performance.
This study is published in British Journal of Clinical Pharmacology.
