Q: Do carbonated drinks leach calcium from bones? Does this increase the risk for osteoporosis? Can drinking soda make a diagnosed case of osteoporosis worse?

A: The best answer I can give to both of your questions is "maybe."

A number of studies in recent years linked carbonated drinks with osteoporosis.

Data from the Framingham Osteoporosis Study (American Journal of Clinical Nutrition, 2006) looked at carbonated drink consumption among more than 1,400 women and 1,100 men. They found that women who drank the most caffeinated cola had the lowest bone density. The biggest effect was seen for those drinking three or more caffeinated cola drinks per day.

The effect was weaker for non-cola and non-caffeinated carbonated drinks. And they saw no link between any of these drinks and bone health in men.

More recent studies have come to similar conclusions. One study found a higher rate of bone fractures among teenagers who drank carbonated drinks compared with those who did not.

But no one knows if there is a true cause-and-effect relationship between carbonated drinks and weak bones. Something else about soda drinkers may explain this. For example, maybe soda drinkers exercise less and smoke more than those who don't drink sodas regularly. Differences like this could lead to more osteoporosis among soda drinkers.

But if there is a direct connection, there are a number of possible explanations:

-- Soda drinkers may drink less milk or eat fewer foods that contain calcium.

-- The phosphate in carbonated drinks may block or slow how calcium is absorbed (although the drinks do not necessarily "leach" calcium out of the bone).

-- Caffeine in sodas may weaken bones by impairing growth and development over time.

Until we know more, I think it makes sense for people with osteoporosis to limit carbonated drinks. Cutting back is unlikely to cause harm and might just help. Other steps you can take include:

-- Get enough calcium, at least 1,000 to 1,200 mg/day.

-- Get enough vitamin D, for people with osteoporosis, 1,000 units per day..

-- Get plenty of weight-bearing exercise, such as walking

-- Take medicines to build up bone, such as alendronate (Fosamax) or risedronate (Actonel), as prescribed by your doctor.

-- Don't smoke.

-- Don't drink too much alcohol.

-- Reduce the use of medications (such as corticosteroids) that can decrease bone strength.

Talk to your doctor about your bone health and what you can do to keep your bones healthy. This may include changing what you drink.

Robert H. Shmerling, M.D. is associate physician at Beth Israel Deaconess Medical Center, Boston, and associate professor at Harvard Medical School. He has been a practicing rheumatologist for over 20 years at Beth Israel Deaconess Medical Center.

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