Gum disease is common and unpleasant, but, according to a growing body of evidence, it could also play a role in a surprising range of seemingly unrelated health problems.
Plaque — a sticky substance that contains bacteria — builds up on teeth. If it is not brushed away, the bacteria can irritate the gums.
The gums may then become swollen, sore, or infected; this is referred to as gingivitis.
In general, gum disease can be treated or prevented by maintaining a good oral health regime.
However, if it is left to develop, it can result in periodontitis, which weakens the supporting structures of the teeth.
Gum disease, which is also called periodontal disease, is widespread. According to the Centers for Disease Control and Prevention (CDC), almost half of adults in the United States have some degree of gum disease.
The mechanisms behind periodontal disease are relatively well-understood, and newer research shows that this health problem may play a role in the development of a number of other conditions, including Alzheimer's disease, cancer, and respiratory disease.
In this Spotlight, we will cover some of the surprising links between gum disease and disparate health issues.
Gums and the brain
Although spatially the gums are near the brain, one wouldn't normally associate dental complaints with neurological conditions.
However, some studies have found a link between periodontal disease and tooth loss and cognitive function. One study looking at cognitive performance followed 597 men for up to 32 years. The authors conclude:
"Risk of cognitive decline in older men increases as more teeth are lost. Periodontal disease and caries, major reasons for tooth loss, are also related to cognitive decline."
Researchers have also linked periodontal disease with an increased buildup of beta-amyloid in the brain — the neurological hallmark of Alzheimer's.
Other experiments have produced evidence that one type of bacteria commonly found in cases of periodontitis — Porphyromonas gingivalis — can be found in the brains of individuals with Alzheimer's.
Following on from that discovery, in a more recent study, researchers showed that P. gingivalis infection boosts the production of beta-amyloid in the brain.
In this study, the researchers paid particular attention to an enzyme produced by P. gingivalis called gingipain. They found that this protease was toxic to tau, another protein that plays a pivotal role in Alzheimer's.
It is worth noting that other researchers have concluded that beta-amyloid is produced in response to a pathogen. The way we view Alzheimer's is slowly changing.
In the future, scientists hope that targeting gingipain enzymes might help stop neurodegeneration in some people with Alzheimer's disease. They have already designed a gingipain inhibitor, which they are testing in humans.
The researchers hope that it will "slow or prevent further neurodegeneration and accumulation of pathology in [Alzheimer's disease] patients."
The heart of the matter
Although not everyone with heart disease has gum disease, and not everyone with gum disease has heart disease, there does appear to be a correlation.
Of course, individuals who smoke or drink large quantities of alcohol are more likely to have both oral and cardiovascular issues, but there appears to be more to the relationship than shared risk factors alone.
Whether gum disease is an independent risk factor for heart disease is still being discussed, but there are some theories as to how the two might be related.
Some think that the link could involve inflammation.
Primarily, inflammation is a response to irritants or pathogens; it is a protective mechanism. However, if it continues for an extended period, it can damage tissues and organs.
It is possible that inflammation in the gums sets off a cascade that, ultimately, sparks inflammation in the cardiovascular system.
Alternatively, the link between heart and gum diseases may be due to bacteria.
Bacteria in the gums can enter the blood supply and be propelled to distant destinations, including the heart, where they can cause inflammation and damage.
As evidence that this is possible, researchers have shown that P. gingivalis is the most commonly found bacterial species in the coronary artery.
Cancer risk increase
Once again, gum disease and cancer do not, on the surface, appear to have much in common.
A study published in 2008 investigated tooth loss and cancer in 48,375 men. The authors concluded that there was, indeed, a link between gum disease and cancer. They write:
"Periodontal disease was associated with a small, but significant, increase in overall cancer risk."
Another, more recent, study involving more than 68,000 adults found a strong association between gum disease and overall cancer risk; the link was also significant between gum disease and pancreatic cancer.
Why might this be the case? A paper published in Nature goes some way toward an explanation.
The researchers found that an enzyme produced by a type of bacteria commonly associated with gum disease — Treponema denticola — commonly appears in certain tumors of the gastrointestinal system.
The enzyme, known as T. denticola chymotrypsin-like proteinase, helps the bacteria invade tissue in gum disease. The researchers found that it also activated other enzymes that promote cancer cells as they advance into healthy tissue.
Some well-known risk factors include smoking tobacco, drinking alcohol, and hypertension. According to some scientists, periodontal disease might also increase the risk of erectile dysfunction.
For instance, the authors of a literature review published in 2016 identify an association between erectile dysfunction and chronic periodontitis.
In fact, they suggest "that physicians should refer patients with [erectile dysfunction] to oral healthcare providers for a comprehensive oral evaluation and treatment."
Because erectile dysfunction and gum disease have shared risk factors, including smoking and diabetes, it has been difficult to ascertain whether gum disease is an independent risk factor for erectile dysfunction.
Although sexual dysfunction and gum health seem worlds apart, there are a number of potential ways in which they could influence each other.
Once again, inflammation might be the culprit. As mentioned earlier, inflammation in one part of the body — the mouth, in this instance — can spread via chemical messengers in the blood and impact other regions.
Erectile dysfunction is often due to malfunctioning blood vessels; specifically, the smooth muscles lining the walls of blood vessels lose their ability to relax. This is referred to as endothelial dysfunction, and it prevents vasodilation in the penis and, consequently, erections.
A so-called proinflammatory state may promote endothelial dysfunction and, therefore, increase the risk of erectile dysfunction.
However, the link has not been definitively proven. The authors of a review published in 2016 concluded that, although this link seems likely, more large-scale studies are needed.
Gums and lungs
Of course, the mouth is a shared gateway to the gums and the lungs, making a link between gum and lung diseases less surprising than some of the others that we have encountered.
A study published in February 2019 investigated the records of 1,380 men. The authors found a significant relationship between chronic periodontitis and a reduction in respiratory function.
This link remained significant, even after controlling for confounding variables, such as smoking.
Once again, inflammation may be the link between the two conditions. If the tubes in the lungs that carry air are inflamed, they become narrower and air flow is restricted.
Aside from the probable role of inflammation, bacteria present in the mouth might also be breathed into the lungs. Once in the lungs, the bacteria could trigger infections that directly lead to inflammation.
A recent meta-analysis investigated potential links between gum disease and lung cancer. The authors concluded that "patients with periodontal disease are at increased risk of developing lung cancer."
In their paper, they outline some potential ways in which gum disease might increase lung cancer risk. For instance, breathing in bacteria, such as P. gingivalis, from the mouth could cause infections.
Similarly, enzymes produced during the course of gum disease might pass into the lungs. Once there, they could help pathogens take root and colonize the lung tissue.
These changes spark inflammation; over the long term, inflammation causes changes in cells that raise the likelihood of cancer developing.
The take-home message
One could read this article as a worrying collection of conditions made all the more likely to occur, courtesy of gum disease.
If we adopt the opposite approach, though, the take-home message could be much more positive: Good dental hygiene may reduce our risk of developing a range of serious health problems.
As the authors of the lung cancer analysis, mentioned above, write, "periodontal disease is a preventable and treatable disease." Managing it at an early stage might reduce the risks of a multitude of ills.