How Many Sodas Does it Take To Hurt Your Kidneys?

The downsides of drinking soda reach beyond the truly devoted guzzlers of the world, according to a surprising new study presented at Kidney Week 2013. It only takes two cans a day to do a number on your kidney function.

Researchers from Osaka University in Japan examined nearly 8,000 university employees with normal kidney function. The participants were divided into three groups: those who drank one soda a day, those who enjoyed two, and those who abstained from the fizzy stuff. After a 3-year follow-up, more than 10% of the group that drank two sodas a day developed proteinuria—an abnormally high level of proteins in urine that’s a risk factor for end-stage kidney disease.

While researchers haven’t pinpointed the exact mechanism that links soda consumption to proteinuria, they have a few ideas. “Oxidative stress and inflammation induced by fructose, which is more active sugar than glucose, may play an important role,” says study author Ryohei Yamamoto, MD, PhD, a professor in the department of geriatric medicine and nephrology at Osaka University.

Animal studies have previously explored fructose’s effect on the kidneys, including a recent one out of Case Western Reserve University that found consuming moderate amounts of fructose for 13 days straight caused kidneys to become sensitive to a protein that regulates salt in rats. Researchers believe this sensitivity can lead to kidney failure,hypertension, and more.

You're not off the hook with diet soda, either—participants in the Japanese study drank both diet and the regular stuff. And proteinuria isn’t only dangerous for your kidneys, says Dr. Yamamoto. He says it's also associated with cardiovascular disease and even mortality.