Any way you look at it, soda bubbles are trouble. Researchers have known for years that carbonated beverages are bad for bone health, presumably because soda has replaced calcium-rich milk and fortified juices in kids' diets. Now Grace Wyshak, a Harvard biostatician, has found a particularly worrisome link between cola and bad bones among girls who engage in vigorous sports. Girls in the ninth and tenth grades who combine cola with heavy sporting activity fracture their bones five times as often as equally athletic girls who don't consume soft drinks. "The bone mass girls acquire during adolescence is directly related to their bone mass in postmenopausal years, so there could be serious problems when today's teenage cola drinkers get older," Wyshak explains. She's still not sure what causes the trouble. "It likely has something to do with hormones and the high levels of phosphoric acid in cola drinks," she says. Other carbonated beverages seem to have less of an impact, and nobody has observed the same effect among teenage males, at least not yet. But Wyshak thinks cola-swigging boys deserve closer study as well.