Health experts have long suspected a link between soft drinks and reduced bone mineral density. Now, research released Friday suggests that phosphoric acid in cola drinks may be the problem.
Tufts University researcher Katherine Tucker examined the bone mineral density readings of more than 2,500 adult men and women and surveyed their soft-drink consumption patterns, distinguishing among carbonated cola drinks, carbonated non-cola drinks, and carbonated caffeine-free and diet soft drinks. She found that women -- but not men -- who drank more than three 12-ounce servings of cola per day had 2.3% to 5.1% lower bone mineral density in the hip than women who consumed less than one serving of cola per day.
Similar results were seen with diet and caffeine-free cola beverages but not with non-cola carbonated beverages.
"This remains a very controversial area," Tucker says of the research presented at the annual meeting of the American Society for Bone and Mineral Research in Minneapolis.
"But it seems that the phosphoric acid in cola drinks has a negative effect on bone. When you have phosphoric acid in a cola beverage, the excess phosphoric acid binds to calcium in the gut," which keeps the calcium from being absorbed.
It's also possible that phosphoric acid can adversely affect parathyroid hormone levels in the body, which regulate bone density, Tucker says.
Other studies are needed to test the theory, she adds, explaining that some researchers doubt that the level of phosphoric acid in cola drinks is high enough to contribute to low bone mineral density.
Experts have suggested that many people replace milk with soft drinks as they grow older, a move that leads to lower bone mineral density because of the loss of calcium from milk.
But in the new study, "we did not find that people drinking cola beverages drank less milk than other people," Tucker says. "Adults don't drink much milk anyway."
Still, the interaction between diet and bone mineral density is complex, she noted, as evidenced by the fact that no link between cola and lower bone mineral density was found in men.
"Men have different beverage consumption patterns," says Tucker. "They drink more alcohol, and alcohol can be protective of bone in some ways." In research awaiting publication, Tufts researchers found that beer appears to protect bone, possibly due to its silicone content.
In other research presented at the meeting, data from the Framingham Study, an observational study of thousands of Framingham, Mass., residents, showed that a high level of the chemical homocysteine in the blood is associated with future risk of osteoporosis and hip fracture.
Women with high homocysteine levels had double the hip fracture rate, and men with high levels had four times the increase, compared to people with low homocysteine levels.
The levels can be influenced by diet, particularly vitamin B-12 and folate, and by some medications.
Osteoporosis affects 10 million Americans; an additional 34 million have low bone density and are at risk for the disease. Osteoporosis can lead to hip fractures and physical decline, and it is a major cause of nursing-home admissions among the elderly. The disorder is more prevalent in women.
Also, Holocaust survivors who were 17 or younger at the onset of World War II are now reporting hip fracture rates that are more than 10 times higher than individuals of the same ethnic group and age who did not live under Nazi occupation.
Researchers from Hadassah University in Jerusalem suggest that poor diet and harsh conditions had an adverse effect on the amount of bone accumulated during the growth period of childhood and adolescence.