Ask the Doctors

Dear Doctor: I was informed several years ago that carbonated drinks weaken bones, leaching the calcium from them. Is this true? What would be considered an acceptable amount for a teenager or a woman past menopause? Would carbonated spring water be better?

Dear Reader: Sodas are ubiquitous in our society. Even schools sell them. Further, both parents and children often use sodas as their primary source of liquids, shunning simple water -- the essence of life. The evidence between soda intake and obesity risk is irrefutable. Now let's look at the evidence on bone density.

Almost 20 years ago, a study published in the Journal of Bone and Mineral Research found that cola-drinking rats had lower levels of calcium, higher levels of phosphorus, lower levels of vitamin D and higher levels of parathyroid hormone than water-drinking rats. They also had lower bone density in the femur (hip) bone.

A 2006 study published in the American Journal of Clinical Nutrition assessed the amount of cola and non-cola carbonated beverages, both with and without sugar, consumed by 1,125 men and 1,413 women. The study followed participants for 25 years and then checked their bone mineral densities. The authors did not find an association between non-cola carbonated beverages and lower bone mineral density in either men or women. Nor did they find an association between cola consumption and lower bone density in men. However, women who drank cola sodas had significantly lower bone mineral density than those who didn't drink sodas, regardless of whether the sodas contained sugar or artificial sweeteners.

Another American Journal of Clinical Nutrition study published in 2014 followed more than 73,000 women between the ages of 30 and 55 for 30 years. At the end of the study, they found that the rate of hip fracture was 10 percent greater among women who drank more than 10 sodas (of all types) per week, compared to those who did not drink any sodas.

The authors then compared women with the same body mass index who drank soda versus those who didn't. Here the authors found a significant correlation between soda intake and hip fractures. Women who drank five to 10 sodas per week had a 16 percent increased risk of hip fractures, and women who drank more than 10 sodas per week had a 42 percent increased risk of hip fractures. The increased rates of hip fracture were seen in both caffeinated and non-caffeinated sodas, as well as colas and non-colas.

Carbonated spring water is simply water with dissolved carbon dioxide gas, but that's not to say it isn't acidic. The pH level is between 3 and 4 -- higher than sodas' roughly 2.5 pH -- while water has a pH of 7. The acidity could potentially pose a problem, but a study published in the British Medical Journal in 2005 found no difference in markers for bone turnover between postmenopausal women who drank carbonated mineral water for eight weeks and postmenopausal women who drank plain mineral water.

My advice is: Make plain water your primary source of fluid. Also, and this is important: Minimize the amount of sodas that you and your teenager drink. In addition to their link to obesity, they do seem to increase the risk of low bone density and bone fractures.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)

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