Phosphoric Acid

Phosphoric acid, used in many soft drinks (primarily <a href="http://en.wikipedia.org/wiki/Cola" title="Cola" >cola</a>), has been linked to lower bone density in epidemiological studies.

For example, a study<a href="http://en.wikipedia.org/wiki/Phosphoric_acid#cite_note-4" >[5]</a>using dual-energy X-ray absorptiometry rather than a questionnaire about breakage, provides reasonable evidence to support the theory that drinking cola results in lower bone density. This study was published in the <a href="http://en.wikipedia.org/wiki/American_Journal_of_Clinical_Nutrition" title="American Journal of Clinical Nutrition" class="mw-redirect" >American Journal of Clinical Nutrition</a>. A total of 1672 women and 1148 men were studied between 1996 and 2001.

Dietary information was collected using a food frequency questionnaire that had specific questions about the number of servings of cola and other carbonated beverages and that also made a differentiation between regular, caffeine-free, and diet drinks. The paper cites significant statistical evidence to show that women who consume cola daily have lower bone density. Total phosphorus intake was not significantly higher in daily cola consumers than in nonconsumers; however, the calcium-to-phosphorus ratios were lower.

On the other hand, another study suggests that insufficient intake of <a href="http://en.wikipedia.org/wiki/Phosphorus" title="Phosphorus" >phosphorus</a> leads to lower <a href="http://en.wikipedia.org/wiki/Bone_density" title="Bone density" >bone density</a>. The study does not examine the effect of phosphoric acid, which binds with <a href="http://en.wikipedia.org/wiki/Magnesium" title="Magnesium" >magnesium</a> and <a href="http://en.wikipedia.org/wiki/Calcium" title="Calcium" >calcium</a> in the digestive tract to form salts that are not absorbed, but rather studies general phosphorus intake.<a href="http://en.wikipedia.org/wiki/Phosphoric_acid#cite_note-5" >[6]</a>

A clinical study by Heaney and Rafferty using calcium-balance methods found no impact of carbonated soft drinks containing phosphoric acid on calcium excretion.<a href="http://en.wikipedia.org/wiki/Phosphoric_acid#cite_note-heaney-6" >[7]</a> The study compared the impact of water, milk, and various soft drinks (two with caffeine and two without; two with phosphoric acid and two with citric acid) on the calcium balance of 20- to 40-year-old women who customarily consumed ~3 or more cups (680 mL) of a carbonated soft drink per day. They found that, relative to water, only milk and the two caffeine-containing soft drinks increased urinary calcium, and that the calcium loss associated with the caffeinated soft drink consumption was about equal to that previously found for caffeine alone. Phosphoric acid without <a href="http://en.wikipedia.org/wiki/Caffeine" title="Caffeine" >caffeine</a> had no impact on urine calcium, nor did it augment the urinary calcium loss related to caffeine. Because studies have shown that the effect of caffeine is compensated for by reduced calcium losses later in the day,<a href="http://en.wikipedia.org/wiki/Phosphoric_acid#cite_note-7" >[8]</a>

Heaney and Rafferty concluded that the net effect of carbonated beverages—including those with caffeine and phosphoric acid—is negligible, and that the skeletal effects of carbonated soft drink consumption are likely due primarily to milk displacement.

Other chemicals such as <a href="http://en.wikipedia.org/wiki/Caffeine" title="Caffeine" >caffeine</a> (also a significant component of popular common cola drinks) were also suspected as possible contributors to low bone density, due to the known effect of caffeine on <a href="http://en.wikipedia.org/wiki/Calciuria" title="Calciuria" class="mw-redirect" >calciuria</a>.

One other study, involving 30 women over the course of a week, suggests that phosphoric acid in colas has no such effect, and postulates that caffeine has only a temporary effect, which is later reversed. The authors of this study conclude that the skeletal effects of carbonated beverage consumption are likely due primarily to milk displacement<a href="http://en.wikipedia.org/wiki/Phosphoric_acid#cite_note-heaney-6" >[7]</a> (another possible <a href="http://en.wikipedia.org/wiki/Confounding_factor" title="Confounding factor" class="mw-redirect" >confounding factor</a> may be an association between high soft drink consumption and sedentary lifestyle).