A bone to pick with cola

Bones are made of calcium phosphate, a molecule made when phosphoric acid combines with calcium. So one would think that phosphoric acid in the diet would be good for bones.

Or maybe not. Phosphoric acid combines in the digestive system with any calcium it finds, and binds tightly to it, making the calcium unavailable to the body. Since calcium is needed in many important functions, when there is no calcium in the diet, the body gets the needed calcium from its storehouse of the mineral -- the bones.

Bones are constantly being built up and torn down by cells called osteoblasts and osteoclasts. The former store calcium in the bones, and the latter mine the bones for calcium when it is needed elsewhere.

When acid levels in the diet are high, the body neutralizes the acid with calcium from the bones. This can happen when high protein diets are not supplemented with enough fruits and vegetables and other alkalinizing foods to buffer the resulting acid. The kidneys cannot excrete urine that has a pH lower than 5. The acid content of cola has a pH of 3. It would take over 8 gallons of water to dilute a can of cola down to pH of 5. Since it can't do that, the body neutralizes the acid with calcium from the bones.

Many proteins are made of sulfur containing amino acids that produce sulfuric acid when they are metabolized. This acid needs to be buffered or neutralized before it can be excreted.

By locking up calcium before it can be absorbed, and by raising the acid levels that need to be neutralized by buffers from the bones, the phosphoric acid in cola drinks causes bone loss through two mechanisms.

Where the effects are most noticed is in children, especially adolescent girls, and women. It is not clear why men are slightly less affected by phosphoric acid in soft drinks, and the hypotheses range from hormonal activity to larger alcohol intake by men. Cola drinks have been associated with kidney stones in both men and women, however.

Mineral water is alkalinizing. Perhaps a switch to water or alkalinizing fruit and vegetable juices would be a good idea.

Not all studies blame the acid in cola. Some blame milk displacement as the primary reason soft drinks affect bone loss, and link caffeine to calcium in the urine.

Maybe switching to milk...