IMPACT OF GENDER AND AGE ON URINARY WATER AND MINERAL EXCRETION RESPONSES TO ACUTE CAFFEINE DOSES

Urinary excretion of water, calcium, magnesium, potassium, sodium and chloride are increased for two hours after caffeine consumption in several different human populations of differing age and gender. The results of six previous studies were combined in order to investigate possible differences in response to caffeine-induced water and mineral excretion due to age or gender. 144 subjects were included: 92 females and 52 males, mean age 43 year, range 13-78. Each fasting subject drank a beverage on two separate mornings, one without caffeine and a second to which 6 mg/kg lean body mass caffeine was added, then urine was collected for two hours afterwards. Preload fasting total mineral and creatinine excretion was lower in women than men and increased with age. Urinary excretion of creatinine and phosphorus was not affected by caffeine. When mineral excretion was expressed as ratios to creatinine or increments above preload excretions, both genders had similar, significant caffeine-induced increases in water, calcium, magnesium, potassium, sodium and chloride excretion. Neither gender or age impacted urinary mineral excretion response to acute caffeine doses when expressed per creatinine excretion or incremental excretion.