The influence of lead and other metals (calcium, magnesium, zinc) on the development of pregnancy-induced hypertension.

Abstract

Objective: To identify any contributory effects that the elements - lead, calcium, magnesium and zinc, may have on the development of pregnancy-induced hypertension (PIH). Design: A case-control study with women enrolled during their third trimester. Population: A total of 143 pregnant women, including 33 PIH cases. The Maltese population was chosen as it was previously shown to have high levels of circulatory lead. This lead would have been inactively stored in bones for decades, but could be released during conditions of increased bone turnover, such as pregnancy. Methods: PIH was diagnosed as blood pressure readings above 140/90 mmHg at two successive measurements, at a four-hour interval. Blood lead was analysed by electrothermal atomic absorption spectrometry (AAS), and serum zinc by flame AAS, using the technique of standard addition. Serum calcium and magnesium were analysed by photometrical methods, and ionised calcium by ion selective electrode. Results: PIH cases had statistically significant higher blood lead levels than the normotensive controls, even after correcting for the haematocrit. No differences were noticed between the two groups regarding calcium (ionised and total), magnesium, and zinc levels. Blood lead was significantly related with blood pressure, even after correction for the body mass indices and age. No relationships with blood pressure were shown for ionised calcium, serum magnesium or zinc levels. Lead: ionised calcium ratio showed a stronger association with blood pressure than lead alone. Blood lead showed a significant negative relationship with ionised calcium. There were no relationships between lead and the other metals. Conclusions: In addition to the known fetal effects of lead, this study exposed an effect on the maternal side. Blood lead influenced at least part of the blood pressure variation and PIH development. All efforts should be made to reduce the population's exposure, as lead's influence appears to have no threshold of influence. These findings encourage dietary manipulations with the intent of reducing blood pressure and lead during pregnancy. This could involve calcium supplementation so as to reduce bone resorption, and hence lead release from bone.