Your body isn’t a finely-tuned machine. It’s a reinforced pile of goo that spends its day trading off costs and benefits. One of those costs is the tartar building up on your teeth because of the surprising source of your saliva.
Calcium, and fossilized bacteria, build up on your teeth every day in tartar. (Before regular dental hygiene was a thing, they could build up to the point where they were wider than the tooth.) The bacteria are invaders, but the calcium comes from your own body. It’s one of the many components of saliva.
That is fair enough. Studies have found that people with saliva that’s high in calcium have more intact teeth than people with low levels of calcium in saliva. Then again, they also have gums that bleed a lot more when probed. The calcium levels are a trade-off that your body makes—more teeth for eating, but more painful gums.
Where does that calcium come from? And where do the anti-bacterial compounds found in saliva come from? While some of the stuff in your blood comes from the salivary glands in your cheeks, the glands themselves don’t produce the liquid that trickles into your mouth every day. They’d have a tough time producing so much. Some people make a liter of saliva a day.
The liquid comes from your circulatory system—as in blood. The main reason you don’t bleed directly into your mouth is your salivary glands strain out the hemoglobin, and any other compounds that are better left in your circulatory system. This is why, in addition to having calcium and the many antibacterial cells that guard your blood swishing around your mouth, you have a mouthful of hormones. They hitch a ride in from your blood, which is why some medical tests for hormone disorders only need a saliva sample and not a blood sample. So as you go about your day, tasting your food or perhaps kissing your significant other, consider that you’ve spent your life tasting a mouthful of your own filtered blood.
[Source: Gut, by Giulia Enders]