Zinc levels in maternal milk: the influence of nutritional status with respect to zinc during the third trimester of pregnancy.

OBJECTIVE

To study the relationship between nutritional status with respect to zinc during the third trimester of pregnancy and levels of the same mineral in transition milk (days 13 and 14 of lactation) and mature milk (day 40 of lactation).

DESIGN

Longitudinal study.

SUBJECTS

A group of 57 healthy, lactating mothers aged between 18 and 35 y (27 +/- 3.7) whose pregnancy and labour were attended by the Department of Obstetrics and Gynaecology of Cuenca INSALUD Hospital, Spain.

INTERVENTIONS

Zinc intake during the third trimester was determined by recording the consumption of foods over a five day period and by registering zinc provided by dietary supplements. Zinc levels in maternal serum during this stage of pregnancy, and in transition and mature milk, were determined by atomic absorption spectroscopy.

RESULTS

During pregnancy all subjects showed zinc intakes lower than those recommended. Only one pregnant subject took a supplement that provided extra zinc (1 mg/d). Subjects with an intake of lower than 50% of that recommended (L) (43.9%) showed significantly lower serum and mature milk zinc levels than did those with higher intakes (H) (56.1%) [12.0 +/- 1.5 mumol/L and 28.7 +/- 6.2 mumol/L compared to 13.3 +/- 2.6 mumol/L and 33.1 +/- 8.0 mumol/L respectively]. 56% of L subjects and 28.6% of H subjects showed serum zinc levels of less than 12.2 mumol/L. 8% of L subjects and no H subjects showed less than 11.5 mumol/L of zinc in maternal milk.

CONCLUSIONS

The diet conditions maternal serum zinc levels during pregnancy and those of milk during lactation. Though all subjects showed intakes clearly below those recommended, low levels in serum or milk were much rarer. These results support the idea that there is a need to reset the limits of normality for serum and milk zinc levels. Further work in this area may confirm that the present recommended intakes of zinc be modified.