Purdue University has again canceled its annual cricket-spitting contest due to the coronavirus pandemic. If it resumes in 2022, insects will be far from the only thing flying through the air. Lots of spit will spray out as well. Getting saliva on the cricket makes it more aerodynamic, notes Thomas Turpin, the retired insect scientist who started the contest 25 years ago.
No one at Purdue has analyzed the cricket contestants’ spit. But it’s probably more watery than the saliva in your mouth when you rest or drool, says Lissa Davis, a graduate student at the university’s SPIT Lab. Food scientist Cordelia Running heads this lab, whose acronym stands for Saliva, Perception, Ingestion and Tongue.
Even psychology can affect how much spit your mouth makes. Several years ago, Running and a colleague learned that people spat out more of a test liquid if they thought it was an extract of rabbit hair instead of tea. That’s not necessarily the case for cricket spitting.
Saliva seeps and swishes around our mouths all the time. Most of us don’t give it much thought. But a growing cadre of scientists sees saliva as a font for important research. Their recent findings have been shedding light on how saliva is made, how it interacts with our sense of taste and how it can help diagnose when things go wrong inside us.
The average adult produces about a liter of saliva per day. Over a lifetime, that “compares to about the size of a tank truck,” says Stefan Ruhl, a dentist and oral biologist who works at the University at Buffalo in New York.
Saliva production is highest during the day, especially at mealtimes. About 99 percent of that goo is water. The rest is mostly proteins and salts. Most of our spit comes from three major pairs of salivary glands.
He and others recently showed where the saliva glands get some of the major proteins they put into human saliva. This work offers clues to the role of certain genes.
Saliva’s water and other chemicals have many roles. For one, saliva acts like a gatekeeper. “It keeps the bad stuff out,” Ruhl says, and “lets the good stuff in.” Some chemicals in our spit help with healing and protect against infection.
Saliva also provides a moist home for our mouths’ microbiome. That’s the group of bacteria and other organisms that live there. Most are harmless, although some bacteria do cause cavities and other problems.
Finally, saliva helps us eat. As our mouths water, saliva not only softens and shapes food into wads but also helps us swallow them. That’s thanks to mucins, Ruhl says. These long strings of amino acids have sugars jutting out from them, like bristles sticking out from a bottle brush or mascara brush.
Research at Purdue’s SPIT Lab looks more closely at how saliva affects our taste experience. Saliva “mixes with food when you eat it,” Davis points out. Chemicals in that saliva may react with our meal.
For example, many people avoid vegetables that taste bitter. That’s especially true for young children, Davis says. Some poisonous plants are bitter, she notes, so we may have evolved receptors in the mouth to alert us to bitter compounds so that we can avoid potential poisons.
In one study, people drank different beverages for much of a month. During one week they drank three glasses each day of almond-based chocolate milk. Another week the drink was made with cow’s milk. On a third week, they drank no chocolate milk at all. After each week, these people provided samples of their saliva.
This suggests our bodies change the recipe of proteins in our saliva in response to what we regularly eat or drink. Says Davis, “It would make sense that your body would kind of adjust to make that sensation more pleasant for you.”
Their data don’t show how much the protein changes might alter what foods taste like. In fact, people reported little change during the study in their sense of the milk’s flavor.
Sure, we’ve all heard of saliva tests to sample for DNA, and even sometimes COVID-19. But such tests are now expanding into brain injuries, such as concussion. Its symptoms can include headaches, nausea, double vision and dizziness.
Steven Hicks is a pediatrician at Pennsylvania State College of Medicine in Hershey. He notes that when a concussion occurs, levels of certain signaling molecules in the nervous system may change. Known as micro-RNAs, or miRNAs, they tell cells to make or stop making proteins for different jobs.
This study analyzed saliva from 538 people. Most were under 25 years old. The researchers knew which people had sustained a concussion. They used data from the first 400 or so to create a computer model.
Saliva tests probably won’t replace current concussion analyses in children and adults, Hicks says. These include brain scans, blood tests and watching for symptoms. The team’s test could, however, help as an additional screening tool.
The team described its findings last October in the International Journal of Molecular Sciences.
Parents have told Hicks they really appreciate when he doesn’t have to stick needles in their kids’ arms. Several years ago he wanted to do a study on autism. This family of disorders affects how the brain develops. Only one parent would let Hicks’ team draw a child’s blood for research.
Genetic factors seem to play a large role in autism. Studies also suggest that the gut’s microbiome could be involved. Hicks and others used saliva to test the mouth’s microbiome.
Other recent studies suggest saliva can help screen for marijuana use or help diagnose type 1 diabetes. And Brazilian scientists showed how uric acid in saliva can help estimate the build-up of body fat in teens.
Saliva can even help scientists gauge anxiety, notes Nattinee Jantaratnotai, who works at Mahidol University in Bangkok, Thailand. There, she studies the effects of medicines and other compounds.
Scientists have only begun to delve into what most of saliva’s many ingredients do. A “really challenging” aspect of spit science, Davis admits, is that “everything seems to matter.”