According to a new study published in the American Journal of Clinical Nutrition, women are drinking soft drinks in record amounts and this daily habit may be wreaking havoc on their bones.
Building on previous observational studies that found the intake of carbonated beverages was associated with reduced bone mass and increased fracture risk, researchers from the Creighton University Osteoporosis Research Centre in Omaha set out to pinpoint the specific components of soft drinks that may be to blame.
Other researchers speculate that the phosphoric acid and caffeine in soft drinks can drain calcium from the bones and increase calcium loss.
"Our results indicate that colas and other soft drinks are a significant problem," said co-author and renowned calcium researcher Robert P. Heaney, M.D., professor of medicine from Creighton University.
"However, it is not what they contain, but rather what they do not contain, the nutrients needed for bone health.
If women are drinking multiple cans of soft drinks every day, it means they are probably not drinking enough milk, which supplies the right mix of calcium, vitamin D and other nutrients that bones need."
The study examined the urinary calcium losses of women aged 20 to 40 who regularly consume soft drinks (two to seven 12-ounce cans daily).
Four carbonated beverages were tested, two with caffeine and two without caffeine.
The results were compared to water and two milks, plain and chocolate.
While this study did not find that phosphorus or caffeine in carbonated beverages caused significant losses in urinary calcium (although the caffeinated sodas produced some loss of calcium), the researchers believe the impact of soft drinks should not be underestimated.
"The issue is somewhat more complicated because carbonated beverages contain several other substances known to influence urinary calcium (such as sodium and sugar), which could inevitably lead to bone loss; even their volume may exert some influence," Dr. Heaney explained.
"And the damaging effects on bone may be due to other factors rather than simply the increase in urinary calcium loss."
In addition, according to Dr. Heaney, even a small influence on the amount of calcium excreted can add up, and the cumulative effect can have a big impact on bones, particularly when it is not offset by additional calcium in the diet.
Perhaps the most damaging effect of soft drinks is the displacement of milk, Dr. Heaney concluded.
Over the past 30 years, consumption of carbonated beverages has tripled, while milk intake has decreased by 40 per cent.
The researchers warn that soft drinks appear to be the beverage of choice today among adult women, the group with the lowest calcium intake and the highest risk of osteoporosis.
9 out of 10 women fail to meet current calcium recommendations, and one in two women over the age of 50 will have an osteoporosis fracture in her lifetime.
The National Academy of Sciences recommends that women aged 19 to 50 get 1,000 mg of calcium per day, which is equivalent to about three glasses of milk.
Getting enough milk is even easier today because of the wide variety of flavours and packaging available.
"Instead of grabbing a soft drink to satisfy a sweet tooth, women should savour milk's flavours," says Ann Marie Krautheim, MA, RD, a registered dietitian for the National Dairy Council.
"Flavoured milks not only taste great, but they also provide a dynamite nutrient package of calcium plus eight other essential nutrients."