Peer-reviewed, data-analysis and experimental study, people
A new study led by the University of Portsmouth suggests our saliva is stronger than we thought.
The research, published in PLOS One , is the first to examine how drinking apple juice affects saliva's lubricating properties using advanced scientific techniques.
Saliva plays an important role in preventing friction and bacteria in our mouths by creating a slippery film on teeth. It also helps repair early damage to tooth enamel. We know this protective layer is affected by different drinks, but until now it wasn't clear exactly in what way and for how long.
Using 32 healthy participants, scientists analysed how rinsing with apple juice for one minute impacts saliva, before doing the same test using water. They found the mouth's natural defences bounce back remarkably quickly when exposed for a short period of time.
While apple juice temporarily disrupted saliva, the effects began to wear off within just 10 minutes. Even more surprisingly, the team discovered that water actually caused greater initial disruption to saliva's protective properties - but the recovery time was much faster.
"We were genuinely surprised by these results," said lead author Dr Mahdi Mutahar from the University of Portsmouth's School of Dental, Health and Care Professions .
"It's long been believed that apple juice, like other acidic drinks, immediately harms our oral health, including the teeth. However, our research shows that saliva plays a vital role in protecting and quickly repairing the mouth to prevent lasting damage.
"But it's important to point out that long-exposure to apple juice - by repeatedly drinking it or not washing your mouth out with water after taking a sip - can have a long-term negative effect on our oral hygiene."
The team used cutting-edge laboratory techniques - normally used in engineering - to measure exactly how slippery and protective saliva is before and after drinking apple juice and water. These included tribology, protein analysis, and real-time monitoring of salivary films.
Protein players
The study revealed which specific proteins in spit are affected when you drink apple juice; immunoglobulins, cystatins and carbonic anhydrase decrease significantly, while mucins - the main lubricating proteins that keep everything slippery - remain stable.
Understanding these proteins could lead to new toothpastes and mouthwashes designed to boost the mouth's natural defenses.
Dr Mutahar explained: "The key finding is that one brief drink of apple juice isn't harmful - the lubrication comes back to normal and the proteins in saliva do their protective work.
"The biggest shock though was discovering that rinsing mouths with tap water actually caused more friction and disruption than apple juice. The Portsmouth water we used contains minerals that seem to interfere with saliva's lubricating proteins, more than the fruit juice did."
The Portsmouth tap water contains high concentrations of ions including sodium, potassium, and magnesium, which interfere with saliva's main lubricating protein, mucin.
The research also uncovered an unexpected link between fruit juice consumption and the mouth's immune system. The decrease in immune-related proteins suggests that what we drink or eat may influence our oral immune defenses, which in turn may affect the general immune system.
"What's new is discovering that what we drink can actually change how our mouth's immune system works," explained Dr Mutahar. "The ingredients in apple juice may be influencing oral immune defences, possibly affecting overall immune response in ways we're only just beginning to understand."
Changing your hygiene habits
The research suggests that moderate consumption of fruit juice may not be as immediately damaging as once thought, thanks to saliva's rapid recovery abilities.
However, the team cautions this doesn't mean fruit juice is harmless - repeated exposure throughout the day could overwhelm the mouth's natural repair mechanisms.
"Think of it like a cut on your skin," said Dr Mutahar. "Your body can heal small, occasional damage quite well, but if you keep reopening the wound, it becomes a problem. The same principle applies here."
A few simple behaviour changes could minimise any negative effects of drinking apple juice:
Drink quickly, don't sip: "Don't expose your teeth for long periods of time," advises Dr Mutahar. "Have your apple juice fairly quickly rather than sipping it constantly throughout the day."
Rinse immediately: Rinse your mouth with water immediately after drinking apple juice. This helps remove lingering acids, which is especially important for sugary drinks like apple juice, as sugar is a major contributor to tooth decay too.
Use a straw: This reduces contact between the acidic drink and your teeth.
Allow recovery time: If you want a second drink, have a short drink of water, wait, and then have your second one. This allows saliva to work and those important proteins to buffer and protect.
The research team is now exploring the effects of repeated exposure - specifically, what happens when people consume acidic drinks several times a day. Most importantly, they aim to investigate how apple juice impacts the teeth directly, rather than just saliva, and how it compares to the effects of pure acid. They are also planning to test deionized water (with minerals removed) to confirm whether Portsmouth's hard water findings apply to all water types.
Future research could look into adding protective proteins to everyday drinks - a move that might not only neutralise harmful acids but also strengthen the mouth's natural defences by supporting saliva's ability to repair and protect teeth.
The research was conducted in collaboration with Professor Anwesha Sarkar from the University of Leeds, a leading international expert in food-saliva interactions, and involved participants aged 18-56 from the Portsmouth area.
Professor Sarkar, a professor of colloids and surfaces in the University of Leeds School of Food Science and Nutrition, said: "This is fascinating research which shows how open collaboration can improve our understanding of food and drink, and its effects on our oral health.
"By combining the knowledge and expertise of Dr Mutahar and the dental team in Portsmouth with my expertise in material science, specifically friction and real-time adsorption measurements, we have opened up new areas of possibility when it comes to dental health and protecting our teeth with our very own, highly potent saliva. In time I hope this collaboration leads to more improvements in dental care and development of oral devices."
