Calcium, phosphorus, and magnesium: how much is too much for infant formulas?

Despite the use of metabolic balance studies and measurements of bone mineral content, it is difficult to assess the requirements of Ca and P in growing infants. From observations made forty years ago with cow's milk formulas it is obvious what is too much calcium and phosphorus in infant formulas. These observations were utilized in the development of "humanized cow's milk formulas" in the 1950s. Though the total concentrations of Ca and P have been greatly reduced in these formulas, the Ca/P ratio imbalance, compared to human milk, persists. Infants fed these formulas still receive a relative phosphorus load, and cases of neonatal tetany are still occasionally reported. Thus, formula-fed infants have higher serum P and lower serum Ca concentrations than do human milk-fed infants. Unlike Ca and P, the magnesium concentration of infant formulas is similar to that of human milk, and Mg toxicity from formulas has not been reported. Like Ca and P, however, it is difficult to determine the growing infant's requirement for magnesium. The available information does not favor either increasing or decreasing the present concentrations of Ca, P or Mg in infant formulas. The upper limit for these minerals should remain at the present concentrations: 45-50 mg/dl (65-75 mg/100 kcal) for Ca, 30-40 mg/dl (48-58 mg/100 kcal) for P and 12 mg/dl (18 mg/100 kcal) for Mg.