DEAR DOCTORS: Our nine-year-old loves science and has become obsessed with saliva. He recently learned in school that it helps prevent disease, and now he wants to know more. My wife and I are glad he's curious and hope you can help. What is saliva? Does it really help people stay healthy?
DEAR READER: Your budding scientist has asked a great question. When you think about the many ways our bodies protect us from potential danger, saliva isn't the first thing that generally comes to mind. And yet, it's a crucial line of defence. It makes sense, considering the mouth is a key entryway for potential pathogens. These include dangerous microorganisms or toxins that may be contained in food or drink, as well as those that can hitch a ride into the mouth on fingers, surfaces, objects or even a kiss. And while we rarely think about the constant presence of saliva in our mouths, it's actually a pretty remarkable substance.
While awake, a healthy person produces two or more pints of saliva per day. During sleep, however, that amount drops to near zero. The majority comes from three major pairs of salivary glands, with additional amounts coming from an array of hundreds of minor glands. The fluid these glands produce lubricates the mouth and throat, moistens food so that it can be chewed and swallowed, makes possible the sense of taste and washes away particulates. Because saliva has a near-neutral pH of 6.3, it helps protect tooth enamel by maintaining the acid-base balance in the mouth. And while it's made up of 99% water, the remaining 1% contains a number of important organic and inorganic molecules. That makes saliva a biofluid.
Some of the compounds in saliva, including the enzymes lipase and amylase, kick-start the process of digestion by beginning to dismantle fats and carbohydrates the minute you begin to chew. And others, as your son has learned, play an important role in protecting the body from disease. Saliva is stocked with an array of antiviral, antimicrobial and antifungal compounds. These include hydrogen peroxide, lactoferrin and strings of simple proteins that dismantle, damage and neutralise many potential pathogens.
Recent research has revealed that tiny sugar molecules found in saliva, known as glycans, play an important role in preventing a certain fungus that is present in the mouth from becoming a health problem. Saliva also contains certain compounds that play an important role in wound healing. If you've noticed that when you accidentally bite your tongue or chew your cheek, the injury heals surprisingly fast, saliva is the reason.
We'll wind things up with a quick mention of the potential of saliva as a diagnostic tool. Some readers may have already undergone a so-called "spit test" for Covid-19, which identifies the Sars-CoV-2 virus more quickly (and comfortably) than testing with nasal swabs. Researchers are also learning that various proteins and other compounds in saliva become detectably altered in response to certain types of disease. These discoveries have led to a promising new screening test for oral precancers and cancers. Universal Features Syndicate
Dr Eve Glazier is an internist and associate professor of medicine at UCLA Health. Dr Elizabeth Ko is an internist and assistant professor of medicine at UCLA Health.
