Researchers in Western Australia recently examined the relationship between chocolate intake and bone density and strength in older women.

A group of 1001 women between the ages of 70 and 85 years participated in the study. Chocolate intake was classified as—less than once a week, 1 to 6 times a week, or once a day. Bone density and strength were measured using a series of laboratory studies.

The results, published in the January 2008 issue of the American Journal of Clinical Nutrition (AJCN), showed a direct relationship between chocolate intake and bone density and strength. After adjusting for potential confounders, women who consumed chocolate daily had 3 percent lower whole-body bone density compared to those who ate chocolate six times a week or less.

Is Cola a Culprit Too?
Similar results were found with cola beverages. Researchers examined a group of 2500 women approximately 60 years of age who drank an average of five carbonated beverages a day, four of which were cola. They found that drinking cola was associated with lower bone mineral density regardless of age, menopause, total calcium and vitamin D intake, or smoking or drinking alcohol. Bone density among women who drank cola daily was 4 percent less, compared with women who didn’t drink cola.

Why Would Chocolate and Cola Affect Bone Density?
It’s not known precisely why cola drinks and chocolate are linked to higher bone loss in women in these studies, and the authors note that more research is needed before any conclusions can be made. Prior studies have proposed that people who drink lots of sodas are less likely to drink calcium-containing beverages like milk. However, that was not the case in this study. Two components found in cola—but not in most other sodas—are phosphoric acid and caffeine. Chocolate contains theobromine, caffeine, and oxalate. Again, it’s unclear if these chemicals are the culprits.

The phosphorus part of phosphoric acid is a major component of bone mineral content, along with calcium. However, if phosphorus content of the diet is too high compared to calcium, it can alter hormone levels in a way that could increase bone loss. This should not be a problem if calcium intake is adequate.

Caffeine can cause a very small reduction in calcium absorption. Some studies reported that caffeine also increases calcium loss in the urine, however this was later shown to be false when evaluated over a 24-hour time period. Experts agree that the solution is not to decrease caffeine intake, but to insure that calcium intake is adequate.

Oxalate inhibits calcium absorption and dark chocolate increases calcium secretion. But whether these effects are sufficient to explain the observations is uncertain. The effects of theobromine are unknown.

No Chocolate? No Cola?
First of all, there is no evidence to show that chocolate or cola cause bone loss—only that an association was found between the two. Secondly, some studies (here and here) show that eating chocolate can actually be beneficial. While the same cannot be said for cola, if you are the type of person who doesn’t like to drink water, adding a few colas to your daily diet is unlikely to have negative effects on your bones as long as your diet contains adequate bone nutrients (calcium, phosphorus, vitamin D, magnesium, zinc, and protein).

Last but not least, commonsense tells us that too much of even a good thing can be harmful, so the best advice is to eat and drink in moderation. And remember that the recommendation to eat “five a day” applies to fruits and vegetables!

Those so inclined can still, “Have a Coke and a Smile.”
As for me, “Pass the chocolate, please.”