Soda (nor cola) does not cause osteoporosis.
However, studies have shown a correlation between cola consumption and increased risk in osteoporosis. The National Osteoporosis Foundation lists several risk factors, noting that:
Studies ... suggest that people who regularly drink cola drinks may be at greater risk of bone loss. Other non-cola carbonated soft drinks do not appear to have these same risks.
But cola consumption is just one of a plethora of risks.
In Soda and Osteoporosis: Is There a Connection?, author Gina Shaw examines the link between the two and has several informative quotes from reputable doctors and researchers in the field. Some choice quotes from the article:
"There is an association between people who have high soda intake and risk of fracture, but that's probably due to the fact that if they have a high soda intake, they have a low milk intake. Those things have been shown to be linked in various studies. But when you look at the ingredients of the soda and give those to healthy people and measure what it does to their calcium composition, nothing happens at all."
-- Robert Heaney, MD, FACP, a professor of medicine at Creighton University
Other possible culprits include, noted in the aforementioned article, include:
- Phosphoric acid. From the article: "Phosphorus itself is an important bone mineral. But if you're getting a disproportionate amount of phosphorus compared to the amount of calcium you're getting, that could lead to bone loss."
- Caffeine, which can interfere with calcium absorption.
In conclusion, cola does not cause osteoporosis. And it is believed the negative effects of cola consumption can be counterbalanced. As the National Osteoporosis Foundation notes in its risk factors list, "You can help make up for the potential loss of calcium from sodium, excessive protein, too much caffeine and cola drinks by making sure you get enough calcium every day."