The finding has them excited about the prospect of using the drugs -- called bisphosphonates -- to help prevent cancer in healthy people, but other experts are less enthusiastic.
"The lower risk of colorectal cancer risk seen among bisphosphonate users in this study is intriguing," Eric Jacobs of the American Cancer Society, who wasn't involved in the study, told Reuters Health by e-mail.
"However, these results should be interpreted with caution and require confirmation by additional studies."
The new work looked at 933 women with colon cancer, whose average age was just over 70. The researchers then found a comparison group of women without the disease, who matched the first group in age, ethnicity and clinics where they received treatment.
Earlier studies have found that women taking bisphosphonates have a lower risk of breast cancer. But it was unclear if that effect could be chalked up to the drugs, because the condition they are meant to treat -- bone thinning, or osteoporosis -- is tied to low estrogen levels, which also cuts breast cancer risk.
Colon cancer, on the other hand, has not been linked to estrogen, said Dr. Gad Rennert of the Carmel Medical Center in Haifa, whose findings are published in the Journal of Clinical Oncology.
His team found that women who had been taking bisphosphonates -- mainly the drug alendronate (Fosamax), which costs around $10 per month in the U.S. -- for at least a year had a considerably lower risk of developing colon cancer later on.
Even after considering other factors tied to the disease -- like aspirin or statin use and eating lots of vegetables -- their risk was 59 percent lower than that of women who hadn't taken the drugs.
According to the American Cancer Society, one in 19 men develops colorectal cancer at some point, and slightly fewer women do. The disease is the third leading cause of cancer deaths in the U.S.
Rennert said in an e-mail that alendronate is used by millions of women across the globe and has few side effects. The long-term effects are less well-known, however, and in rare cases it can cause bone death of the jaw, which would be important if healthy people were to take it.
Also, not all patients asked to participate in the study agreed, which could limit the results further.
Jacobs of the American Cancer Society added that one earlier study from the UK had found no link between bisphosphonate and colon cancer. Indeed, it found a higher risk of throat cancer in patients on the medication.
"Based on current evidence, bisphosphonates should not be used for prevention of colorectal cancer," Jacobs said. "Fortunately, there are proven ways to help prevent colorectal cancer. In particular, all Americans, 50 or older, should get a screening test so that precancerous polyps can be detected and removed before they turn into cancer."