Plasma zinc levels throughout pregnancy: a study in Jamaican women, with relevant aspects of nutrition

ABSTRACT

In a prospective study plasma zinc levels were determined by atomic absorption spectrophotometry in 135 Jamaican women over a two year period. A total of 1237 such determinations were made at fixed intervals throughout pregnancy. Each patient was investigated at 15, 20, 25, 30, 35 and 38 weeks gestation, in labour, and once in the early and in the late puerperium. Zinc being an essential trace element with a wide physiological role in many aspects of metabolism, supplementary studies on the relationship between zinc, folic acid, vitamin A, dietary intake in general, taste acuity and weight gain in pregnancy were undertaken. Results show that plasma zinc levels are lowered during pregnancy, moreso during the second trimester. The levels rise significantly during labour and then fall rapidly towards normal during the puerperium. Daily dietary zinc intake was of the order of 8-10 mg/day (the RDA for pregnancy being 15 mg/day) while protein intake averaged 67 g/day (the RDA being 80-90 g/day). Average weight gain in pregnancy was 12 kg. Plasma vitamin A and red cell folate levels were within normal range in all patients, indicating that there was no state of zinc deficiency interfering with the absorption of these vitamins. Clinical observations and laboratory investigations revealed no signs of any dietary deficiency among the patients. Viewed together, all the facets of this study suggest that the pattern of fall of plasma zinc in pregnancy is a normal physiological change not related to socio-economic status, parity or age. It is concluded that the lowered plasma zinc observed in pregnancy does not reflect a state of true zinc deficiency nor even a state of inadequate dietary zinc intake; it is most likely due to the heavy demand for zinc in the developing fetal tissues and by the expanding maternal blood volume (AU)