Could arsenic harm you… if you don’t get enough?
The USDA Grand Forks Human Nutrition Research Center in North Dakota has spearheaded many animal studies that point to nutritional value for arsenic. The data suggest that there is a threshold for arsenic toxicity and that possibly too little dietary arsenic could also be detrimental. These studies in animals suggest arsenic is essential to fertility and reproduction.
Most nutrients have a safe range and a point of toxicity. Ultratrace elements like arsenic rank among them. Perhaps, as Forrest H Nielsen, Ph.D., of the United States Department of Agriculture, Agricultural Research Service, Grand Forks Human Nutrition Research Center in North Dakota (and the University of Wisconsin) recommends, referring to an "Apparent beneficial intake (ABI)" seems more appropriate for the [ultratrace] elements with beneficial, if not essential, actions that can be extrapolated from animals to humans; these elements include arsenic, fluoride, lithium, nickel, silicon and vanadium.”
Arsenic appears to be one of those nutrients that are neither totally toxic nor completely benign. It has a small range of safety within which we derive benefit. We may need 5 times more arsenic than vitamin B12 if early calculations prove correct, but we dare not exceed one-quarter milligram.
USDA research has accumulated circumstantial evidence that suggests arsenic is essential. The estimated daily dietary intake calculated by researchers for these elements is 12-50 micrograms, satisfied by most typical diets.
We can conclude that arsenic will almost never need to be a dietary supplement. We apparently get enough from our diets. We can also presume from animal studies, that arsenic is probably essential for fertility, reproduction, as well as growth and survival of the newborn and mother in mammals, including humans. If those animal studies from several species can indeed be extrapolated to humans, arsenic may also be important to cardiac health. It may help maintain normal mitochondrial cell membrane function in heart muscle cells.
(Perhaps the only subset of humans who might possibly require arsenic supplementation would be hemodialysis patients. Arsenic deficiency contributes to the increased death risk of hemodialysis patients, and therefore, arsenic supplementation of patients with extremely low serum arsenic concentrations should be considered.)
 Uthus EO, Davis C.,Dietary arsenic affects dimethylhydrazine-induced aberrant crypt formation and hepatic global DNA methylation and DNA methyltransferase activity in rats., Biol Trace Elem Res. 2005 Feb;103(2):133-45.
 Nielsen FH, How Should Dietary Guidance Be Given for Mineral Elements with Beneficial Actions or Suspected of Being Essential?, J. Nut., 0022-3166/96, p. 2377S, 1996
 Uthus EO, Seaborn CD, Deliberations and evaluations of the approaches, endpoints and paradigms for dietary recommendations of the other trace elements. J Nutr. 1996 Sep;126(9 Suppl):2452S-2459S.