Obesity or Diabetes,Soda is driving the most common chronic disease in the world.

As more municipalities consider levying a soda tax—Philadelphia is the latest—legislators should consider the impact of not just obesity and diabetes, but rampant tooth decay.

Tooth decay and cavities, collectively called "dental caries," is the world's number one chronic disease, according to a 2010 study. Tooth issues are especially acute in children: In the US, more than half of children ages 6-8 year olds had dental caries in 2011-2012, according to the Centers for Disease Prevention and Control. But adults are suffering too. More than a quarter of Americans ages 20-44 had untreated dental caries in the same period.

Dental caries cause problems far beyond the mouth, Dr. Karen Sokal-Gutierrez, a clinical professor at University of California, Berkeley, told Quartz. Mouth pain can lead to malnutrition and loss of sleep. For children, this can translate into less focus at school, and even lower attendance, as a 2011 study found. "That's also reducing their educational potential," she says, leading to a reduction in their "future economic potential." Tooth decay in adults has also been linked to heart disease and preterm births.

While sugar has long been recognized as a source of tooth decay, when it comes in the form of soda, it presents a double threat. Bacteria in the mouth feed on sugar, producing acids that damage tooth enamel and lead to cavities. Soda, though, is already acidic. "The sugar and acid together are like a double whammy to a tooth," Mary Hayes, spokesperson for the American Dental Association and pediatric dentist, told Quartz. (Diet soda is still acidic and, therefore, not protective against tooth decay.)

It's not just that sodas lead to tooth decay, Marion Nestle writes in her book Soda Politics; they are "a principle cause." (emphasis hers) She cites several studies, including a 2012 meta-analysis in PLoS One that found consumption of soft drinks "was associated with about 2.4 fold risk of dental erosion," significantly higher than the other risk factors including juice (0.90 fold risk), sports drinks (1.58 fold) and milk (0.67 fold).

Regular flossing and toothbrushing are important, says Sokal-Gutierrez, but can't undo the harm caused by continuously sipping soda over extended periods of time. "No amount of daily toothbrushing and trips to the dentist every six months is going to stop the process," she says.

Soda sales are declining in the US, but 1 in 3 adults still drink a sugar-sweetened beverage, including soda, fruit juice, sweet tea and energy drinks, at least once each day, according to a recent report from the CDC.

The American Beverage Association, which represents major soda makers, told Quartz that "it is inaccurate to single out one small part of the diet as a unique driver of dental health challenges," citing genetics, diet and oral hygiene habits as other factors. In her book, Nestle answers: