The authors of the report wrote in the American Journal of Clinical Nutrition: "Because BMD is strongly linked with fracture risk, and because cola is a popular beverage, this is of considerable public health importance."
Studies in teen girls have tied heavy soft drink consumption to fractures and lower BMD, the researchers note, but it is not clear if this is because they're drinking less milk, or if it is due to any harmful effects of soda itself.
To investigate this question in adults, the researchers measured BMD in the spine and at three points on the hips in 1,413 women and 1,125 men participating in a study of the bone-thinning disease osteoporosis.
While there was no association between soft drinks in general and BMD, the researchers found that women who drank the most cola had significantly less dense bones in their hips.
Cola consumption had no effect on BMD in men.
Women who drank more cola did not drink less milk, but they did consume less calcium and had lower intakes of phosphorus in relation to calcium.
Cola contains phosphoric acid, the researchers note, which impairs calcium absorption and increases excretion of the mineral. Caffeine has also been linked to osteoporosis, they add.
The report said: "No evidence exists that occasional use of carbonated beverages, including cola, is detrimental to bone.
However, unless additional evidence rules out an effect, women who are concerned about osteoporosis may want to avoid the regular use of cola beverages."