Regular cola consumption was linked to lower bone mineral density in all women studied, regardless of other factors such as smoking, alcohol consumption and calcium intake, researchers found.
Low bone mineral density increases the risk of osteoporosis, also known as brittle bone disease.
The news is another hammer blow to soft drinks makers, already struggling against falling fizzy drinks sales as consumers shift to healthier, non-carbonated beverages.
The study, published in the American Journal of Clinical Nutrition, used dietary questionnaires from more than 2,500 people who were part of an osteoporosis study in the US. Their average age was around 60 years.
The results were similar for regular, diet and decaffeinated colas. "The more cola women drank, the lower their bone mineral density was," said Katherine Tucker, the lead researcher and from Tufts University.
Men appeared to be unaffected, despite drinking slightly more cola per week on average.
Suspicions on what may cause cola to damage bone density initially rested on an ingredient called phosphoric acid. Tucker called for more controlled studies on this.
"Physiologically, a diet low in calcium and high in phosphorus may promote bone loss, tipping the balance of bone remodelling toward calcium loss from the bone. Although, some studies have countered that the amount of phosphoric acid in cola is negligible compared to other dietary sources such as chicken or cheese."
Another reason researchers suspected phosphoric acid was because it is not generally present in non-cola beverages. Other fizzy drinks that were not cola-based did not appear to affect bone density, the study found.
Cola drinks Coca-Cola and Pepsi remain two of the biggest-selling soft drink brands in the world. Cola made up more than 70 per cent of fizzy drinks consumed by those taking part in the recent osteoporosis study.
Consumption of carbonated soft drinks, although now stagnating in mature markets, rose by 300 per cent in the US alone between 1960 and 1990.