The body content of iron is regulated primarily by a controlled absorption from the intestinal tract. This absorptive mechanism normally adapts itself to the body's need for iron, thus protecting against an accumulation of iron, even when moderately excessive amounts are ingested. However, in individuals with latent or overt hemochromatosis, the normal intestinal control is defective, and iron in excess of bodily needs may accumulate in the tissues. The incidence of this rare metabolic disorder is not known. Because iron deficiency is a leading nutritional deficiency disorder in the United States and because iron fortification of foods constitues an important public health measure in correcting iron deficiency, the use of forms of irion of low bioavailability seems inappropriate for food fortification. It is evident that use of iron of low bioavailability, no matter how safe, will not satisfy the intended purpose of fortification. For this reason, the Select Committee believes that food should be forified with iron forms of reasonably adequate bioavailability, meaning those that demonstrate by some standardized assay at least 50 percent of the bioavailability of ferrous sulfate. The avoidance of iron overload from fortified foods might be approached by limiting both the amont of added iron and the foods to which it is added. However, overall questions of iron overload are not answered in this report and deserve separate study, with due consideration for the various forms and amounts of iron intake from all sources, including vitamin-mineral supplements. Regular monitoring of the iron nutritional status of the population is essential in this connection. Experimental data are sparse for most of the forms of iron considered in this report. Animal studies have been largely confined to the determination of acute toxicities and bioavailability of specific iron compounds. Such studies have limited relevance in evaluating the possible hazards of the addition of iron to foods. Few reports are available on the effects of long-term feeding experiments. An extensive literature exists on the use of certain forms given as hematinics, but the reports are largely anecdotal and their interpretation is of questionable value. Certain compounds have been employed extensively for many years both as additions to food and in the treatment of iron deficiency with no reported adverse effects. In view of the need for, and wide use of, iron compounds, it would appear prudent to place this historical and anecodotal experience on a scientifically rigorous basis in the reasonably near future. The Select Committee emphasizes the need for well-controlled clinical and chronic feeding studies with most of the individual compounds before confident appraisal can be made of their relative merits or hazards.
No information is available on the metabolism or toxicity of the various substances included under the term iron naphthenate. The Select Committee concludes that: In view of the deficieny of relevant biological studies, it has insufficient data upon which to base an evaluation of iron naphthenate when it is used as an ingredient food can coating films.