It seems like simple, obvious advice: Eat your vegetables, get some exercise, and - of course - floss. Or not.

Turns out that despite being recommended by numerous scientists and universities, the effectiveness of flossing has never been researched, according to a new report from the Associated Press.

The US government has recommended flossing for nearly four decades. But according to the Dietary Guidelines for Americans, a set of recommendations the agency sends out every five years, all of the recommendations have to be grounded in scientific evidence.

And flossing is, well, not.

In its report, published Tuesday, the Associated Press says that it used the Freedom of Information Act to request evidence for the benefits of flossing from the departments of Health and Human Services.

AP never received that evidence. Instead, it got a letter from the government acknowledging that the effectiveness of flossing had never been studied.

So the AP took a look at more than 25 studies comparing conventional brushing alone against brushing plus flossing. They found little to no evidence in favour of flossing.

That comes in sharp contrast to recommendations from basically every major dental hygiene organisation, including the American Dental Association and the American Academy of Periodontology.

Flossing is still considered so crucial to health that it's included in one of the questions in the Living to 100 Life Expectancy Calculator, a tool that uses metrics like diet and exercise to determine your approximate life expectancy.

Many experts say that not flossing lets plaque, the thin film of bacteria that clings to teeth and builds up during the day, to become tartar, a hard deposit that can irritate gums. That tartar buildup can, in turn, cause the gums to recede. Worse, it could create a gap between the gum and the tooth, which could get infected and lead to gum disease.

Numerous reports have linked gum disease to a host of other diseases, including kidney disease, diabetes, and heart disease. Still, no research has concluded that one causes the other - only that there is some kind of relationship between the two.

A 2013 study in the journal CardioRenal Medicine, for example, found that people suffering from chronic kidney disease and gum disease were more likely to die of heart disease, a leading cause of death among those with kidney problems.

The study was unable to pinpoint the precise role gum disease might play in deaths from heart disease, but the researchers nonetheless recommended taking steps to cut back on gum disease in these patients.

People with diabetes have also been found to be at a higher risk of developing gum disease, and people with gum disease have similarly been found to be more likely to develop diabetes.

A 2012 study in the journal Diabetologia suggests that there is evidence supporting the existence of a two-way relationship between the two, but couldn't ultimately conclude that that was the case.

So for now, the topic remains heated. To floss, or not to floss? It remains a question.

This article was originally published by Business Insider.

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