Carbonated beverages and urinary calcium excretion

Background: Intake of carbonated beverages has been associated with increas ed fracture risk in observational studies. The usual explanation given is t hat one or more of the beverage constituents increase urinary calcium. Objective: We assessed the short-term effects on urinary calcium excretion of carbonated beverages of various compositions. Design: An incomplete random block design was used to study 20-40-y-old wom en who customarily consumed greater than or equal to 680 mL carbonated beve rages daily. Four carbonated beverages were tested: 2 with caffeine and 2 w ithout. Two contained phosphoric acid as the acidulant and 2 contained citr ic acid. The study included one neutral control (water) and one positive co ntrol (skim or chocolate milk). Serving size was 567 mL for the carbonated beverages and water and 340 mL for the milks. Beverages were consumed with a light breakfast after an overnight fast; no other foods were ingested unt il urine collection was complete. pH, titratable and total acidity, sodium, creatinine, and calcium were measured in 2-h (morning) fasting and 5-h pos tbeverage urine specimens. Results: Relative to water, urinary calcium rose significantly only with th e milks and the 2 caffeine-containing beverages. The excess calciuria was a pproximate to0.25 mmol, about the same as previously reported for caffeine alone. Phosphoric acid without caffeine produced no excess calciuria; nor d id it augment the calciuria of caffeine. Conclusions: The excess calciuria associated with consumption of carbonated beverages is confined to caffeinated beverages. Acidulant type has no acut e effect. Because the caffeine effect is known to be compensated for by red uced calciuria later in the day, we conclude that the net effect of carbona ted beverage constituents on calcium economy is negligible. The skeletal ef fects of carbonated beverage consumption are likely due primarily to milk d isplacement.