Oral doses of heavy water in the range of several grams, as well as heavy oxygen 18O, are routinely used in human metabolic experiments. (See doubly labeled water testing.) Since one in about every 6,400 hydrogen atoms is deuterium, a 50 kg (110.23 lbs) human containing 32 kg (70.55 lbs) of body water would normally contain enough deuterium (about 1.1 g or 0.04 oz) to make 5.5 g (0.19 oz) of pure heavy water, so roughly this dose is required to double the amount of deuterium in the body.2O --->