Zinc and Normal Nutrition

Recent writers on the biochemistry of zinc have stressed two aspects, the hygienic and the physiological.Various workers in the Department of Physiology, Harvard School of Public Health, have been conducting investigations primarily on the hygienic aspects of the question and have found (1, 2) that the addition of comparatively large amounts of zinc to a normal diet had no apparent ill effect on the well being of cats, rats, and dogs.The zinc, in amounts ranging from 175 to 1000 mg. of zinc oxide per day was administered to cats and dogs over periods of time ranging from 3 to 53 weeks.In the case of rats from 2 to 38 mg. of zinc per day, given as the oxide or a zinc salt, had "no significant effect upon the health of the parents, upon fertility, nor upon the health and early growth of the offspring."It was also noted that the excretion by urine and feces fluctuated with the intake.These investigators found that under natural conditions for the rat, at least, there is no significant variation in the zinc content with age, the amount at birth and at old age being almost identical: 0.038 and 0.040 mg. per gm. of rat; while Fairhall (3) writing from the same laboratory, reported rapid storage of zinc in the young growing rat.The relatively low toxicity of zinc has been more recently confirmed from another laboratory (Heller and Burke ( 4)) so that it seems fairly clear at the present writing that the addition of what may be regarded as excessive amounts of the metal to an ordinary diet is not obviously harmful.It is probable that many of the cases of so called zinc poisoning which have appeared in the