By age 65, 92 percent of Americans have cavities in their permanent teeth, and an average of 3.28 teeth missing or decayed. The answer to why this is may not concern toothpaste ingredients or brushing time, but the lifestyles of ancient humans, as two new studies have discovered.
Humans used to live as hunter-gatherers, meaning they hunted for game and foraged for plants to eat. They were mainly nomadic, following herds to keep their food source. That changed about 10,000 years ago when agriculture was invented. They began to settle down in one place, raising livestock and growing crops for food. The human diet changed, as it now included more starch from the grains they harvested.
The breakdown of starch begins with enzymes in the mouth that split the starch into shorter chains of sugars. The process continues in the stomach and the small intestine until the sugar chains are broken down into individual sugar molecules. This leaves a residue of sugar in a film on and between teeth, creating an ideal environment for the growth of bacteria. Two recent studies have documented how this change in diet caused bacteria associated with cavities and periodontal disease to emerge and eventually become widespread.
One group analyzed the bacterial DNA in samples of tarter from ancient teeth to monitor the changes in the types of bacteria that were present. What they found was a record of how humans have wrecked the bacterial ecosystem in their mouths. The increase in starchy foods caused sugar-loving bacteria to flourish.
With new DNA sequencing technologies, scientists isolated bacterial DNA from 34 teeth of Northern Europeans that are 7,000 to 400 years old, including the last hunter-gatherers from Poland and early farmers from Germany. Hunter-gatherers’ teeth harbored fewer types of cavity-causing bacteria, while early farmers’ teeth revealed a sharp increase in bacteria that cause tooth decay and periodontal disease.
One bacterium, called Streptococcus mutans, contributes to cavities, diabetes and cardiovascular diseases. In the mid-1800s, Streptococcus mutans became even more dominant in the microbial ecosystem inside the mouth, known as the oral microbiome. This change correlates with the Industrial Revolution, which introduced refined grains and sugars. The simple sugars from these processed foods are the basis for microbial fermentation, which lowers the pH of the mouth and causes damage to tooth enamel.
The second study focused on changes in the DNA of Streptococcus mutans alone from the present then going back in time. They sequenced the genomes of the bacterium from 57 people worldwide, then used some clever genetics modeling to calculate when the Streptococcus mutans started expanding and diversifying. They think that occurred about 10,000 years ago, which correlates with the start of agriculture.
Both studies showed that the oral microbiome changed with the development of agriculture. What neither group dealt with are the influences of modern behaviors like using toothpaste, adding chlorine and fluoride to drinking water and more changes to the human diet, particularly the shift to fast food.
Medical Discovery News is a weekly radio and print broadcast highlighting medical and scientific breakthroughs hosted by professor emeritus Norbert Herzog and professor David Niesel, biomedical scientists at the University of Texas Medical Branch at Galveston. Learn more at www.medicaldiscoverynews.com.