The effect of dietary caffeine on urinary excretion of calcium, magnesium, sodium and potassium in healthy young females

Abstract

Twelve female college students drank decaffeinated coffee or tea to which 0, 150 or 300 mg caffeine had been added. Each subject had fasted at least ten hours before drinking each of the three test beverages. Urine samples were collected at one, two and three hours after caffeine consumption. Total urinary three hour excretion of calcium, magnesium and sodium, but not potassium, increased significantly after caffeine intake. The increased output of calcium and sodium was mainly due to significantly increased urinary calcium and sodium concentrations, while the increased output of magnesium appeared to be due to the combination of both a slightly increased urinary magnesium concentration and volume. Total urine volume correlated significantly with dose of caffeine per body weight when 300 mg of caffeine was consumed. The effects of caffeine on mineral excretion were primarily due to changes in mineral concentration and increased urinary volume at one and two hours.