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QUESTION

Is it true that drinking diet pop leaches the calcium out of my bones?

ANSWER

Claims that drinking diet pop causes bone loss are common. A number of studies have shown a link between the consumption of carbonated beverages and reduced bone density, as well as fractures.

Experts still aren't sure how to explain why drinking carbonated beverages, particularly colas, is related to osteoporosis.

One theory is that some of the ingredients in carbonated beverages have a negative effect on the body's calcium balance. They either increase calcium excretion in the urine or decrease calcium absorption from the intestine. Possible culprits include caffeine, phosphorus or phosphoric acid and carbonation.

One study done by researchers at Tufts University in Boston found that women (but not men) who drank three or more cola-based drinks a day had 4-per-cent lower bone density at the hip than those who did not. Women who drank non-cola soft drinks were not affected.

It is important to realize that while studies like this can show an association between soft drinks and bone loss, they don't demonstrate a cause-and-effect relationship. To date, research examining the effects of caffeine and phosphoric acid has not provided conclusive evidence that their consumption is detrimental. Studies of caffeine consumption have shown a temporary increase in calcium excretion into the urine, but that there is no increase in urinary calcium loss over a 24-hour period. Other studies have also found that caffeine causes a very small reduction in calcium absorption.

It has also been shown that when the phosphorous content of a person's diet is higher than the calcium intake, hormone levels may be affected, which can result in bone loss. However, the phosphorus content of a 12-ounce cola is only about 5 per cent of the phosphorus intake of a typical diet. For comparison, there is five times more phosphorus in an eight-ounce glass of milk than in a 12-ounce can of cola.

Another theory is that carbonated drinks don't directly affect calcium balance, but rather that they are consumed in place of other beverages. Several studies have shown that people who drink more soft drinks are less likely to drink calcium-rich milk or fortified orange juice.

While there is no conclusive evidence that diet pop leaches the calcium out of bones, there does appear to be a link between pop consumption and osteoporosis.

This means that people who drink carbonated soft drinks need to ensure that they are getting adequate calcium from other sources.

If you aren't getting enough calcium from your diet (100-1,500 milligrams a day depending on your age) you should take a supplement. In addition, the general recommendation is that caffeine intake should be limited to three to four servings a day.

Dr. Rowena Ridout is an endocrinologist at Toronto Western Hospital and is associate director of the University Health Network/Mount Sinai osteoporosis program.