Even short-term use of popular acid-reducing heartburn drugs may raise the risk of hip fractures, U.S. researchers said on Monday.

The increased risks appeared two years after patients started taking proton pump inhibitors such as Takeda Pharmaceutical Co's Prevacid and histamine-2 receptor antagonists, or H2RAs, such as GlaxoSmithKline's Zantac, researchers at Kaiser Permanente San Francisco told the Digestive Disease Week meeting in Chicago.

Other proton pump inhibitors include AstraZeneca's Nexium and Prilosec, Wyeth's Protonix and Eisai Co Ltd's Aciphex.

A study in August's Canadian Medical Association Journal suggested long-term use of proton pump inhibitors — for at least five years — may raise the risk of hip fractures.

Dr. Douglas Corley, who led the study, said in a statement "the increased risk with short-term use of acid-suppressing drugs suggests that even relatively brief periods of use may be associated with increased risk of hip fractures."

He said patients taking acid blockers should continue treatment at the lowest effective dose, but people at risk of osteoporosis should talk to their doctor about other treatment options.

For the study, Corley and colleagues analyzed data on nearly 40,000 patients taking acid-reducing drugs, and compared them to more than 130,000 patients not taking the drugs.

Patients who had hip fractures were 30 percent more likely to have taken proton pump inhibitors for at least two years, and 18 percent more likely to have taken H2RAs for at least two years.

Risks were lower in people who had taken lower doses.

Those who took less than one pill a day had a 12 percent increase in fracture risk. Patients who took one pill per day had a 30 percent increased risk, while those who took more than one pill a day had a 41 percent higher risk.

People aged 50 to 59 who had been on proton pump inhibitors for more than two years had the biggest increase in fracture risk with taking the drugs, they said.