Have you ever thought about saliva? Most of us probably haven’t, but it is more than just a fluid in your mouth. Much more. Join us as we unravel the incredible science and surprising secrets behind this often overlooked bodily fluid. From its role in digestion to its potential as a diagnostic tool, don't miss out on this fascinating journey into the world of spit!"
M: I’m Professor Megan
S: and I’m Professor Susan, and we’re
Both: Your Nutrition Profs!
M: We are registered dietitians and college professors who have taught more than 10,000 students about health and nutrition. We have answered a LOT of questions about nutrition over the years –
S: Some questions we get asked every year and some are rarely asked but very interesting.
M: We’re here to share our answers to these common (and uncommon) nutrition questions with you.
S: So bring your curiosity and let’s get started.
Both: Welcome to our class!
S: Welcome everyone! We’re so happy that you decided to join us!
M: Our listeners really are the best.
S: Thank you for your continued support. Today we’re answering a question that came from a listener in New Mexico and she asked, “What’s so great about spit?”
M: That is such an interesting question! Spit, or saliva, is one of those bodily secretions that really is taken for granted. But it is such an important and fascinating substance!
S: I mean, think about all of the things we use spit for. Many people believe it has healing properties, right? I mena, if you cut our finger, what do you do? You stick it in your mouth immediately in an attempt to stop the bleeding and heal the cut.
M: I know, it’s used as a cleaning solution too. Just ask any kid whose Mom has dipped the tip of a tissue into their mouth and used it to clean a dirty face.
S: My Mom would do that sometimes. And not just Mom’s use it – some artists use spit to clean paintings, and it does seem to be very effective!
M: We know some of you out there may be a bit grossed out by spit or are anti-spit, but maybe we can change your mind after hearing this episode.
S: Cause spit is amazing.
M: Saliva is a thick, colorless, opalescent fluid with a constant presence and is sometimes called the “bloodstream of the mouth”. Without saliva, getting food from the mouth to the stomach would be nearly impossible.
S: Humans have up to 1,000 salivary glands that produce 1-2 liters of saliva every day – almost all of it while we’re awake. Think of a 2-liter bottle of soda in the grocery store – that’s about how much spit you make…
M: That is a bit!
S: Every day
M: Wow.
S: I mean, if you add that all up it’s about 23,000 liters in your lifetime or more than 6000 gallons.
M: Oh my gosh, that’s enough to fill an above ground swimming pool 15 feet in diameter.
S: That is a lot of spit!!
M: And each drop of saliva contains a complete set of your genes which is really, really cool.
S: Right! I mean, we spit into containers when you have your genes tested like for you ancestry or for nutritional genomics, anything like that.
M: Well let’s start by talking about the salivary glands. As we mentioned, we have about 1,000 of them and all of them are made of fat and tiny cells that secrete fluids called acini.
S: Most of these glands are pretty tiny, only about 2 mm in size, that’s about the size of a pinhead. But a few are quite large. And here is a fun fact, they don’t all secrete the same type of saliva.
M: Wow. Some of the larger glands include 2 that are under either side of your tongue under the mouth floor. These are called sublingual and each is about the size of an almond. These sublingual glands secrete saliva that is thick, like mucus.
S: Another set of these larger glands is located below the jaw and these are called submandibular or submaxillary. The saliva enters the mouth from underneath the tongue. The two submandibular glands together are about the size of a walnut and the saliva they secrete is considered mixed, it’s mucus-y but it’s also watery.
M: But the largest salivary glands – by far – are the parotid glands. These are located just in front of the ears, so basically your cheeks. Each parotid gland is slightly smaller in size than your ear.
S: And these parotid glands are what Mary Roach, author of the book “Gulp” calls “our faithful servants. Whatever you decide to eat boss, I will help you get it down”.
M: That is such a great book!
S: It is!
M: The saliva secreted from these glands is very watery. It enters the mouth from small ducts near your upper molars. The parotid glands provide about 70-90% of the 1-2 liters of saliva that we make every day.
S: You know, that Gulp book is really good and we’ll link it in our shownotes.
M: She’s got some other good books too.
S: She does. She’s an excellent writer.
M: But getting back to saliva… The autonomic nervous system controls the volume and type of saliva that you secrete. And saliva secretion is activated by chewing, smelling, even tasting food in your mouth.
S: Think Pavlov’s dog – the presence of food or just thoughts or smell of food increases salivary secretions.
M: And here’s another fun fact about saliva and dogs. The saliva they create differs based on the type of diet that they eat. Dogs who are fed dry food produce more watery saliva. Dogs on meat-based diets make saliva that is thicker and stringier… so more like mucus.
S: That is interesting! I mean, I love dogs so andy dog-based fun facts always get my attention!
M: Me too! And then another fact! Have you ever heard that dogs' mouths are cleaner than humans?
S: I have heard that.
M: I remember hearing that as a kid… and unfortunately that is not true.
S: Oh that’s interesting… but of course good oral hygiene is important for dogs and for people.
M: Yes!
S: That along with hydration, and not smoking can help keep our mouths and our salivary glands healthy.
M: Excellent advice!
S: Saliva has so many important functions. There are the obvious ones like lubrication of the mouth and throat and moistening food to help with swallowing and washing away food and debris from the teeth and gums.
M: But it also enhances our ability to taste. Saliva spreads what are called “tastants” around the mouth and to the taste buds so that you can enjoy all of the different flavors in a food. We’re actually going to be doing an episode soon all about how we actually taste things so stay tuned!
S: That’ll be a good one. Saliva’s also a disease fighter. It provides antibodies to prevent and fight infections. I mean, have you ever noticed how quickly a sore in your mouth heals compared to sores elsewhere on your body?
M: That is so true! Like when you bite the inside of your cheek –
S: Oh I hate that!
M: …and it feels terrible for a few hours… but by the next day or that night you don’t notice it anymore? That’s due to saliva. It’s so cool!
S: It’s also why we put our cut fingers into our mouths to aid in healing and, guess what? It actually works! Saliva’s been used for centuries for healing. And not just for humans. I mean, animal wounds heal faster if the animal is allowed to lick them. But only within reason, like excessive licking can lead to irritation and apparently only protects against a few types of bacteria.
M: Saliva also helps our teeth in several ways. One thing it does is it protects our teeth from each other. Teeth are the hardest substance in the body. Saliva coats our teeth and without spit teeth would grind against one another which could cause wear and tear damage and could even ground them down prematurely.
S: I never really thought about that, but it’s so true!
M: I know! Saliva also helps keep the surface of your teeth, the enamel, strong. When we consume foods or beverages that are acidic – foods like citrus fruits and juices, wine, and soda – the acids can pull minerals from your tooth enamel. This can lead to tooth sensitivity and it can open the door to cavities and tooth decay.
S: Saliva from the parotid glands comes to the rescue! The help is actually immediate. Saliva neutralizes acid to minimize this mineral loss. It recoats the teeth with minerals like calcium, fluoride, and phosphate ions which can also help to replenish the tooth surface.
M: Saliva secretion is also increased when we eat things that our body perceives as harmful – like spicy food. So again, saliva to the rescue! And we’re going to talk more about this in an episode coming in a few weeks.
S: That’ll be a good one too!
M: Another benefit of saliva is that it helps with digestion. Food digestion begins as soon as food enters your mouth. Saliva contains digestive enzymes like amylase which helps us break down starches. So if you put a piece of bread in your mouth, you’ll notice it immediately begins to fall apart or kind of dissolve. Well that’s the amylase in the saliva breaking apart the starch molecules in the bread.
S: On the other hand, if you put a piece of steak into your mouth and just left it there–
M: Ugh.
S: I know, it’s kind of gross to think about. But it won’t really change much, right? It doesn’t begin to dissolve like the bread does. And that’s because steak doesn’t contain starch, so the amylase doesn’t have any starch to split apart.
M: Another enzyme in saliva is lipase which helps us split apart fats specifically. The levels of salivary lipase are high in infants since their diets are very high in fat, but as we age our levels decline. So by the time we’re adults the levels of lipase in our saliva are actually quite low.
S: Saliva also helps control the levels of microbes that live in our mouth. I mean, we’ve talked about the gut microbiome several times on this podcast–
M: Many times.
S: But well we also have an oral microbiome. It’s rich in anti-microbial compounds like hydrogen peroxide, lactoferrin, and lysozymes which are part of the immune system.
M: Think about it – your mouth is open to outside pathogens through what we eat, drink, and breathe. Without saliva we become more vulnerable to letting these “bad bugs” enter and take hold in our bodies which can lead to infections.
S: And saliva is a great cleanser. Moms and artists! We talked about them before! They use it to remove dust, dirt, and grime from faces and paintings. Those enzymes that help us digest starches and fats, the amylase and lipase, they can also break down these substances in dirt and grime which makes them easier to remove.
M: Yeah, the slight acidity of saliva also provides some cleaning properties. Many people clean their homes with vinegar which is also acidic.
S: I mean, we’re not recommending that you lick your countertops….
M: Absolutely not!
S: That would– that would be wrong on so many levels.
M: Well, saliva has so many more beneficial functions than most people think. Too bad we can’t bottle it and sell it! So have we convinced you yet… that saliva is great?
S: I’m convinced... So if saliva is so amazing why is there such an “ick” factor associated with it? We definitely don’t go around sharing our spit with just anyone.
M: Right, basically family members and intimate partners. That’s it.
S: I mean, we recoil from other people’s spit and from our own once it’s left our mouths! If you spit into a cup, would you drink it later on?
M: Again, absolutely not. Unless I had a really good reason to!
S: I can’t think of what that reason might be….
M: No, I can’t either.
S: And, you know, you never want to make a server angry at a restaurant cause we’ll be like “oh they’re going to spit in our food.” So that’s definitely a bad thing!
M: But in some cultures spit is lucky or protective. Roman Catholic priests used to baptize with spit instead of water based on a passage in the Gospel of Mark, the bible, where Jesus mixed dirt with his spit, rubbed it on a blind man’s eyes, and then he could see.
S: Amazing! And the Greeks often spit on things they wish to protect from the evil eye or that they want to bless for good luck. I mean, now it’s less actual spit and more like the pantomime of spitting, kind of the ph-ph-ph – I can't do it but–
M: Yeah.
S: And that provides luck supposedly.
M: Probably a good idea.
S: So if a Greek spits on you… that’s lucky.
M: Well…
S: …good to know.
M: Good to know! Alright well, as long as our salivary system is working normally, basically we just take it for granted. Which is true with many things.
S: Right.
M: But if there are problems with the system, we definitely know about it.
S: One of these problems is hypersalivation or excessive drooling – the sciencey word for this is sialorrhea. There are two types. There is anterior which is the forward spillage of saliva from the mouth; and there’s posterior which is when saliva drops down the back of the throat and into the airways. This can cause lung irritation called aspiration, which can lead to pneumonia. And some patients can have both.
M: The main cause of excessive drooling is usually some sort of a brain abnormality or injury that causes the inability to manage normal swallowing of saliva.
S: A more common problem is not having enough saliva. The sciency word for too little saliva is xerostomia. And it’s no joke, I mean, dry mouth can lead to all sorts of negative things.
M: I mean, think back to all of the great functions of saliva that we described earlier… without it none of those things can occur. You’re at a higher risk for dental cavities, even tooth decay, having a sore, cracked tongue, and also a type of yeast infection in the mouth called thrush. Speaking and swallowing could become challenging and you may also have trouble tasting anything.
S: All of those things sound terrible.
M: Yes.
S: So who is at risk for xerostomia? Well it’s a common side effect of some medications for things like depression, high blood pressure, and some other conditions. It’s also a common problem for those who have had radiation therapy on the head or neck that can permanently damage your salivary glands.
M: There is also an autoimmune disorder called Sjogren’s Syndrome. This is where your immune system attacks the glands that make moisture in your eyes, mouth, and other body parts. Other symptoms include joint and muscle pain. And the syndrome can also cause damage to your lungs, your kidneys, and your nervous system.
S: Sjogren’s Syndrome predominantly affects women in their 40s and 50s of all races and ethnicities. And it’s not uncommon to also have other autoimmune conditions like rheumatoid arthritis or lupus.
M: Classic symptoms are dry eyes that burn, itch, or feel like you have sand in them. The mouth will be dry and feel chalky. You’ll have potentially all of the problems that low saliva can bring again including increased risk of dental cavities, thrush, and others.
S: And people with Sjogren’s can have other symptoms which can be severe – symptoms like fatigue, acid reflux, vaginal dryness, sleeping issues, memory fog, and even shortness of breath.
M: And there’s no diagnostic test for it yet, so it’s diagnosed based on symptoms. And unfortunately like most other autoimmune diseases, there is no cure.
S: But there are some things that may alleviate your symptoms. They make artificial tears for dry eyes and they make artificial saliva for dry mouth. I never- I mean, the artificial tears you hear about all the time but I never knew they made artificial saliva.
M: I mean if you don’t have a problem with dry mouth, why would you even think about it?
S: Right, right. They also give anti-fungal meds that can treat symptoms of thrush. Additionally steroid injections and minor surgical procedures may be options if you have severe cases of dry mouth. But it’s a pretty terrible condition that needs much better treatment options.
M: One source called the researchers and scientists working to create these improved treatments the “Salivation Army”!
S: That is an amazing name!
M: This “army” is working on improved artificial saliva to keep mouths wet and protected, new drugs to help saliva flow more freely and even gene therapy to repair damaged salivary glands. They’re also trying to build artificial glands that could potentially be implanted in the mouth!
S: Wow!
M: I know!
S: That is amazing.
M: Another problem that can occur are stones in the ducts that can obstruct saliva flow from the glands. These stones are called sialoliths. Common symptoms include swelling, pain, and infection.
S: If you have any of these stones… small ones may be removed by either squeezing them out by hand or by making a small cut in the opening to the duct. If the stones are large though, they made need surgery to be removed. and usually, an Ear, Nose, and Throat specialist would do it. Once the stones are gone the gland almost always recovers, so that’s good news.
M: And you know, salivary glands can even become infected sometimes by these stones, um sometimes for some other reason. But I’ve actually seen at least two cases of infection of the parotid glands, called parotitis, in the hospital that I work at
S: Really?
M: Yeah, one patient looked like they had a lemon just in their cheek!
S: Oh my gosh!
M: And it looked so painful, and they said it was very uncomfortable.
S: Wow, did they just drain it?
M: I believe they drained it and were on antibiotics.
S: Wow! Well with the exception of Sjogrens, most problems with saliva and salivary glands can be treated fairly easily. But do not ignore the symptoms and see your healthcare provider if you experience any of the things we talked about. And you know, your dentist might even notice a problem before you even realize there’s an issue.
M: That’s a good point. Alright, Susan, what’s the bottom line on saliva? What is so great about saliva?
S: Really – the bottom line is that spit is absolutely incredible! It has so many important functions that we mentioned and we really should appreciate it more.
M: And to keep your salivary system healthy, drink plenty of water, don’t smoke, and practice good oral hygiene, so brush and floss regularly.
S: Always good advice. Well that is it for our deep dive into our amazing secretion, saliva. Thanks for joining us today!
M: Join us next time when we will answer the question: “Is ghee better than butter?”
Both: Class dismissed.
S: We hope you enjoyed this episode. You can find the show notes and a list of sources on our website, yournutritionprofs.com.
M: Your homework is to follow us at your nutrition profs on Instagram and to listen to our next episode. You can listen on Amazon Prime, Apple Podcasts, Spotify, YouTube, or anywhere podcasts are found. We’d appreciate it if you’d “like” us, write a review, subscribe, and invite your family and friends to join us too.
S: If you have a nutrition or health question you’d like answered, let us know! We may even do a show about it! Send an email to [email protected] or click on the “Contact Us” page on our website.
M: Thanks to Brian Pittman for creating our artwork. You can find him on instagram @BrianPittman77
Both: See you next time!