According to the US National Osteoporosis Foundation, approximately 55% of people, mostly women, are at risk of developing osteoporosis, a disease of porous and brittle bones that causes higher susceptibility to bone fractures.
How the study was conducted
The researchers analysed dietary questionnaires and bone mineral density measurements at the spine and three different hip sites of more than 2 500 people in the Framingham Osteoporosis Study whose average age was just below 60.
In women, cola consumption was associated with lower bone mineral density at all three hip sites, regardless of factors such as age, menopausal status, total calcium and vitamin D intake, or use of cigarettes or alcohol.
However, cola consumption was not associated with lower bone mineral density for men at the hip sites, or the spine for either men or women. The results were similar for diet cola and, although weaker, for decaffeinated cola as well.
Men reported drinking an average of six carbonated drinks a week, with five being cola. Women reported consuming an average of five carbonated drinks a week, four of which were cola. Serving size was defined as one bottle, can or glass of cola.
"The more cola women drank, the lower their bone mineral density was," says Tucker, who is corresponding author of the study.
Other fizzy drinks seem safe
"However, we did not see an association with bone mineral density loss for women who drank carbonated beverages that were not cola," she said.
Carbonated soft-drink consumption increased more than three-fold between 1960 and 1990. They also note that more than 70% of the carbonated beverages consumed by people in the study were colas. All of these contained phosphoric acid, an ingredient that is not likely to be found in non-cola carbonated beverages.
Previous studies have suggested that cola contributes to bone mineral density loss because it replaces milk in the diet. Tucker found that women in the study who consumed higher amounts of cola did not have a lower intake of milk than women who consumed fewer colas.
However, they did conclude that calcium intake from all sources, including non-dairy sources such as dark leafy greens or beans, was lower for women who drank the most cola.
"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, further controlled studies should be conducted to determine whether habitual cola drinkers may be adversely affecting their bone health by regularly consuming doses of phosphoric acid that do not contain calcium or another neutralising ingredient."
Results still preliminary
Tucker stresses that as with any epidemiological study, the results should be viewed with caution.
"We are not certain why women who drank more cola also had lower bone mineral density," says Tucker.
Although adjustment for fruit juice intake did not change results, women in the study who drank a considerable amount of cola not only consumed less calcium, but less fruit juice as well. Previous studies have also shown that low fruit and vegetable intake may affect bone mineral density.
The message from experts is clear that overall nutritional choices can affect bone health, but "there is no concrete evidence that an occasional cola will harm the bones," says Tucker. "However, women concerned about osteoporosis may want to steer away from frequent consumption of cola until further studies are conducted." - (EurekAlert)