When Indonesian school children who are not iron-deficient take iron pills, they fail to grow normally. (Source: P.Idjradinata, W.E.Watkins, and E.Pollitt. Adverse effects of iron supplementation on weight gains of iron-replete young children, lancet, Vol 343(1994),pp.1252-54.)
When iron supplements are given to Somali nomads or Masai people, their rate of infection increases, even though their iron deficiency is corrected (Source: Nesse and William, Why We Get Sick, p.29).
The high frequency of NEGATIVE RESPONSES to iron supplements in Asia and Africa may reflect the interaction between iron and zinc.
Parents Forewarned. Parents with infants and growing children, beware of the milk-formulas with 'enriched iron, calcium' for strong bone and 'high IQ' gimmick advertisements.
Iron in food or pills interferes with zinc absorption and supplemental iron can aggravate zinc deficiency, which profoundly depresses body immune function.
The recommend daily allowance (RDA) for zinc, 12 to 15 mg/day, is based on the assumption that 40 percent of the zinc that is swallowed is absorbed into your body.
Actually, only 17 to 35 percent of the zinc you eat gets absorbed, depending on what you eat with it. Starch and fiber interfere with zinc absorption, as do calcium and iron. (Source: P.Johnson et al. Zinc bio availability from beef served with various carbohydrates or beverages, Nutrition Research, Vol.10 (1990)pp.(55-62).
Lack of stomach acid, (if after 45 years old) which may be caused by infection or acid-lowering drugs (like antacids), also interferes with zinc absorption.