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Q: I’ve heard that soda, seltzer water, and sparkling water steal calcium from the bones. Is it true?
A. There are warnings from time to time about the harmful effects of soda on bones. The theory is that phosphoric acid (phosphate), used to improve the taste of some sodas, inhibits calcium absorption and causes calcium loss from bones. Fortunately, there is no good evidence that high phosphate intake affects bone metabolism or bone density.
However, soda has been linked to lower bone density and fractures in teenage girls. To examine this association in older adults, researchers at Tufts University looked at data from 2,500 women and men (ages 49 to 69) who participated in the Framingham Osteoporosis Study. They assessed dietary intake and measured bone mineral density (BMD) at the spine and hip.
Non-cola sodas were not associated with lower BMD, although cola consumption was associated with lower hip (but not spine) BMD in women but not in men. The more cola a woman drinks, the lower her BMD. Women who drank more cola did not drink less milk, but had lower calcium intake.
In 2005, the British Journal of Nutrition published the results of a small clinical trial comparing healthy postmenopausal women who drank one liter of non-carbonated mineral water per day to women who drank the same amount of carbonated mineral water. After eight weeks, there was no difference between the two groups in blood and urine tests.
Drinking seltzer water does not appear to increase the risk of osteoporosis or fractures in women. The authors of the cola study suggested that the caffeine in cola may reduce BMD in cola drinkers. Other studies have reported an association between caffeine and lower BMD levels. In some cases, soft drinks supersede calcium-rich drinks such as milk, which may explain the effects of soft drinks on BMD in teenage girls rather than a direct effect on bone, experts say.
So don’t worry, drink seltzer water, but don’t overdo it with caffeinated beverages, whether carbonated or decaffeinated. If you suspect that by drinking seltzer water, coffee, cola, or other soft drinks, you’re cutting back on healthy drinks like calcium and vitamin D-fortified juices and milk. So make sure you get enough calcium through other foods and take a daily vitamin D supplement.