Nov. 2, 2009 -- Diet soda may help keep your calories in check, but drinking two or more diet sodas a day may double your risk of declining kidney function, a new study shows. Women who drank two or more diet sodas a day had a 30% drop in a measure of kidney function during the lengthy study follow-up, according to research presented Saturday at the annual meeting of the American Society of Nephrology in San Diego. "Thirty percent is considered significant,'' says researcher Julie Lin, MD, MPH, assistant professor of medicine at Harvard Medical School and a staff physician at Brigham and Women's Hospital in Boston. That's especially true, she says, because most study participants had well-preserved kidney function at the start of the study.

Diet Soda and Kidneys: Study Details The researchers evaluated 3,256 women already participating in the Nurses' Health Study who had submitted dietary information, including their intake of sugary beverages -- sugar-sweetened drinks, sugar-sweetened soda, and artificially sweetened soda. Sugar-sweetened drinks included soda, fruit juices, punch, and iced tea. Information was also available on measures of kidney function. Their median age was 67. Lin's team looked at the cumulative average beverage intake, derived from food questionnaires completed in 1984, 1986, and 1990. The women replied whether they drank the beverages less than once a month, one to four times a month, two to six times weekly, once daily but less than twice, or twice a day or more often.