Zinc needs and homeostasis during lactation.

During lactation there is an increased maternal loss of essential trace element zinc that is secreted into milk. During the first six months of lactation a mean of approximately 1.1 mg d-1 of zinc is secreted into human milk, which decreases to 0.6 mg d-1 during the next six months of lactation. The increased maternal need for zinc must be met through an increased dietary intake or homeostatic mechanisms which could compensate for the secretion of zinc into milk. These homeostatic mechanisms may include an increase in absorption, reduced excretion (urine and faecal endogenous losses) and the use of maternal pools of zinc, such as bone. Enhanced zinc absorption during lactation has been reported for lactating women whose intake of zinc is less than half of the current recommendation. Urinary zinc excretion by lactating women has also been observed to be significantly decreased up to 6 months postpartum compared to women who have never been pregnant. Approximately 30% of total body zinc is associated with bone. During lactation maternal bone resorption and reduction in one mineral content has been observed. Since urinary zinc excretion is reduced during lactation, this bone resorption could supply a portion of the zinc that is incorporated into milk. Thus, during lactation, homeostatic mechanisms which include an enhanced zinc absorption, reduced urinary zinc excretion and zinc from bone resorption could partially compensate for the secretion of zinc into human milk. These homeostatic mechanisms need to be considered when dietary recommendations for zinc intake are made for lactating women.