The old wives’ tale that a woman loses one tooth for every child she delivers may, in fact, contain a grain of truth. A new study has found that women have had worse dental health than men ever since our ancestors became farmers about 10,000 years ago. That wasn't just because their diets and eating habits changed, as researchers previously believed, but because women who settled on farms were more fertile than nomadic hunter-gatherers. A boost in fertility meant farmers' wives were pregnant more often, which caused changes in their hormones and saliva secretion that rotted their teeth, according to a report in this month's issue of Current Anthropology.
Researchers have known since the 1980s that the invention of agriculture led to more tooth decay, particularly in women. Most researchers have attributed this to dietary and cultural changes that come from settling down. Both men and women began eating more starchy grains, such as corn and wheat, which contain sugars. Changes in the division of labor meant that women were preparing food more than men--and snacking more, because they had access to more food. "You increase carbohydrates and generally you increase the incidence of dental caries," says anthropologist Clark Spencer Larsen of Ohio State University in Columbus.
The shift to farming also set in motion other important biological changes, notes biological anthropologist John Lukacs of the University of Oregon in Eugene. Lukacs did a meta-analysis of studies of tooth decay in 147 collections of tens of thousands of teeth from prehistoric and living humans that lived around the world from 12,000 years ago to 800 years ago. He confirmed that women consistently had more cavities than men when they lived in agricultural societies. He also documented a rise in fertility among women, perhaps in part because they were less nomadic and didn't have to carry children from place to place. Women would have experienced three other factors that occur during pregnancy and increase the number of cavities in women: a boost in female sex hormones; a reduction in the flow rate of saliva and its antimicrobial properties; and an increase in cravings for high-energy, sweet foods.
This comprehensive view of women's oral health is "very smart," says dentist and geneticist Alexandre Vieira of the University of Pittsburgh in Pennsylvania. How much being pregnant contributes to cavities could be tested, says Larsen, by comparing the incidence of tooth decay in women and men in modern populations before and after boosts in fertility. Lukacs agrees: "Our new task is to partition the factors that cause caries--how much is caused by biology and how much by culture," he says. "It's not all or nothing--it's a mixture."