Low zinc intake during exclusive breast-feeding does not impair growth

We studied zinc nutrition in exclusively breast-fed infants whose growth deviated from the norm. Their number fell from 200 at birth to 116 at the age of 6 months and 36 at the age of 9 months. The mothers received 0, 20, or 40 mg Zn++ as sulfate daily. Breast milk intake and concentrations of zinc in milk as well as in maternal and infant serum were measured. Individual zinc concentrations in milk showed channeling. The 20-mg supplement had no effect on the parameters measured. In contrast, 40 mg increased the maternal serum zinc concentration by 2 months and slowed the normal decline of milk zinc concentration by 6 months. Maternal supplementation had no effect on infant serum concentrations; they remained lower than adult levels throughout the 1st year of life. Zinc intake was low (about one-tenth of RDA), but it seemed to be adequate; the serum concentrations of the infants were stable after the age of 2 months. Low zinc concentrations in serum were not associated with impaired growth. On the contrary, the infants with the highest rates of growth had the lowest zinc concentrations. The infant serum zinc concentrations were channeled, but they were also influenced by the zinc intake. Reference values for breast-fed infants are given.