The kidneys are the main organs of the urinary system. They function chiefly to filter blood in order to remove wastes and excess water. The waste and water are excreted as urine. The kidneys also reabsorb and return to the blood needed substances, including amino acids, sugar, sodium, potassium, and other nutrients.
But many popular brands actually contain considerably less than an old-fashioned cup of black coffee. An 8.4-ounce serving of Red Bull, for instance, has a relatively modest 76 to 80 mg of caffeine, compared to the 95 to 200 mg in a typical cup of coffee, the Mayo Clinic reports.
Think again. One Journal of Analytical Toxicology report looked at nine different types of decaffeinated coffee and determined that all but one contained caffeine. The dose ranged from 8.6 mg to 13.9 mg. (A generic brewed cup of regular coffee typically contains between 95 and 200 mg, as a point of comparison. A 12-ounce can of Coke contains between 30 and 35 mg, according to the Mayo Clinic.).