Trace metal requirements of preterm infants

The elements zinc, copper, manganese, molybdenum, selenium and chromium are considered to be essential nutrients in man. It is known that they cross the placenta because they are all present in fetal bodies where they are presumably necessary for normal growth and development. Though deficiency of copper, zinc, selenium and chromium have been reported in man only copper and zinc deficiency have been described in premature infants. Typically, the deficiency develops late (between 3-6 months of age), at a time when the concentration in breastmilk is falling and before a mixed diet has been introduced. This late onset, together with data on body composition, suggests that preterm infants are born with stores--albeit small--of copper and zinc, as they are with iron. The stores may be depleted to a variable extent following birth by dietary insufficiency (particularly total parenteral nutrition), malabsorption and diarrhoea. This leads to severe deficiency in some infants and possibly less severe deficiency in many more, which may pass unrecognised because of difficulties in diagnosis. Dietary provision of a trace element should have two purposes. It should be sufficient to prevent the development of a deficiency state, and to provide enough to enable stores to be formed so that deficiency does not immediately occur if the diet is temporarily inadequate. No case of manganese, molybdenum, selenium or chromium deficiency has yet been described in preterm infants, but no systematic search for deficiency of these elements has yet been undertaken.