For more than a century, medicine has toyed with the idea that bad teeth and bleeding gums could be causing heart disease. The idea is based on the simple observation that the two are often seen together, and pulling a bad tooth was even once considered to be a way of preventing a heart attack.
Plenty of studies showed there was a definite association—people with bad teeth and gums (periodontal disease) are almost twice as likely to suffer from heart disease, for instance—but finding rock-solid evidence of a direct cause-and-effect relationship between the two was more elusive. At best, major studies like the National Health and Nutrition Examination Survey (NHANES) concluded that gum disease was "a risk factor" for heart and artery problems, and it was probably because bacteria from infected gums were escaping into the bloodstream and settling in arteries, causing a similar inflammatory response.
The idea started to take a back seat with the rise of a new theory, which emerged in the 1970s, that 'bad' LDL (low-density lipoprotein) cholesterol—which increased when we ate more saturated fats—was the chief culprit. The theory was promoted by medical researcher Ancel Keys from the University of Minnesota, whose Seven Countries Study suggested that populations that consumed the most saturated fat—from meat, eggs, butter and other dairy products—also had the highest cholesterol levels and the highest death rates from heart disease.1
Kick in the teeth
The final knockout punch to the gum disease theory seemed to have been delivered in 2012, when a team of 13 dental experts reviewed more than 500 papers that had investigated it over the years, and concluded that it was a medical myth. Just because gum disease is often seen in heart patients doesn't mean it causes heart disease, they pronounced. In fact, it could just be that people who don't look after the health of their heart don't care that much about the state of their teeth and gums either.2
A direct causal link was "biologically possible"—gum problems and heart disease are both inflammatory processes, for instance—but other agents were probably at play, such as cigarette smoking, diabetes or aging, the researchers surmised.
Lead researcher Peter Lockhart from the Carolinas Medical Center told journalists: "The message sent out by some in the healthcare professions that heart attack and stroke are directly linked to gum disease can distort the facts, alarm patients and perhaps shift focus on prevention away from well-known risk factors for these diseases." 3
Their definitive statement was immediately accepted by the American Dental Association and the World Heart Foundation, and that seemed to put an end to the matter.
Check your fats
And it was, at least until last summer, when a group of researchers from the University of Connecticut came up with an astonishing discovery—the plaques in arteries don't come from animal fats.
Heart disease is actually 'artery disease,' and the medical term for the process is atherosclerosis, which describes the process where fats, or lipids, stick to artery walls and form plaques. The plaques clog and harden the artery wall, and can cause a heart attack or stroke.
The prevailing saturated fats theory—which is supposed to explain how the plaques got there in the first place—didn't make sense to the researchers; as they pointed out, around half of all heart disease patients have normal levels of LDL or 'bad' cholesterol, while others who eat a lot of fatty foods don't ever seem to get the problem.
Several studies support their maverick view. One found that bad gums were a greater risk factor than high cholesterol levels for heart disease.4
This confusion runs through the medical establishment. Groups such as the American Heart Association say that "decades of evidence" show that eating saturated fats somehow raises cholesterol levels, and yet the original proponent of the idea, Ancel Keys, has denied any association. In 1997, he said: "There's no connection whatsoever between cholesterol in food and cholesterol in blood. And we've known that all along. Cholesterol in the diet doesn't matter
at all unless you happen to be a chicken or rabbit."
So the Connecticut research team took a closer look at some samples of lipids taken from heart patients at a nearby hospital and discovered that they didn't have any of the hallmarks of animal fats from which they supposedly originated. Instead, they came from a specific group of bacteria, called Bacteroidetes—and they can live in our gums.5
Lead researcher Frank Nichols, who studies the links between atherosclerosis and gum disease, said that Bacteroidetes are like "greasy bugs because they make so much lipid; they are constantly shedding tiny blebs of lipids that look like bunches of grapes."
The lipids taken from the heart patients were unique to Bacteroidetes and had a chemical signature that was unlike anything from animal fats. Our immune system sees them as alien invaders, and its attack on them could explain the whole process of atherosclerosis. Enzymes that are released to break down Bacteroidetes start the inflammatory processes that are always seen in heart patients.
Bacteroidetes can also cause gum disease, and this could explain the association between the two problems that is often witnessed by dentists and doctors. But it's not that gum disease causes heart problems—instead, it's a special kind of bacteria and its fatty by-products that cause both.
Although Bacteroidetes can live in the gums, and cause bleeding gums, and in the arteries, and cause heart disease, they start life in the gut. They form one of the two major groups of bacteria in the gut—the other is the Firmicutes—and their job is to break down foods.
Before the Connecticut researchers made their discovery, Bacteroidetes had already been suspected of causing metabolic syndrome, which overlaps with heart disease and diabetes. Jeffrey Gordon at Washington University School of Medicine first proposed the idea in 2005 after he noticed that obese laboratory mice had half the level of Bacteroidetes seen in lean mice, suggesting they were processing food and releasing energy differently. 6
In a study of 12 overweight people who reduced carbohydrate or fat intake for a year, Gordon noted that their levels of Bacteroidetes rose as they lost weight.7
Gordon's observations have been moderated, and even challenged, by other biologists, who have argued that the gut microbiome and its impact on health is far more complex than that; for one, around 99 different subsets of Bacteroidetes have been identified, so what was Gordon actually observing?
What has become apparent is that Bacteroidetes levels are higher in people with type 2 diabetes, often a precursor of heart disease, according to one study of 345 people,8 and supported by similar findings in a group of 53 women with the condition.9 This suggests that Bacteroidetes levels are linked to poor glucose control, a hallmark of diabetes, say researchers at Cornell University.10
If that's true, heart disease is more closely linked with processed food—which often triggers a sudden spike in glucose levels—than it is with saturated fats, claim researchers from UPMC University in Paris. It all points to "the potential problem of our modern lifestyle and the consumption of hyper-hygienic, extensively processed food for human health," they say.11
Whatever the association really.
Signs of gum disease
• Red, swollen or tender gums or pain in the mouth
• Bleeding when brushing or flossing, or after you've eaten hard food, such as nuts
• Receding gums, so that the tooth appears abnormally long
• Loose teeth
• Pus between gums and teeth
• Mouth sores
• Persistent bad breath
• Teeth suddenly feel different when they close together when biting
• Dentures suddenly don't fit as well
It's a bug's life
The bacteria Bacteroidetes—now suspected of being the cause of both gum disease and heart and artery problems—is one of the most common forms of bacteria found in the gut of every warm-blooded animal, including humans. Along with Firmicutes, they break down food and help convert it to energy.
Biologists have noticed that the amount of Bacteroidetes varies between the healthy and the sick, and even between lean and obese people.
Lower levels of Bacteroidetes in obese people suggest their guts are less able to process food properly, and levels increase when people start to lose weight. Most of the research thus far has been restricted to tests on laboratory mice, and only very small human studies have been carried out, so this phenomenon isn't fully understood yet.
People with celiac disease, who are sensitive to gluten, have higher levels of Bacteroidetes (and of other bacteria, too, such as Clostridium and Staphylococcus).