Hypertension caused by low-level lead exposure: myth or fact?

Several reports on the possible association between low-level lead exposure and blood pressure reflect diverging views. This meta-analysis aimed to find a common denominator in the published literature and to estimate whether a relationship exists between blood pressure and levels of lead in the blood. Of the studies reviewed, 23 provided sufficient details to be considered. The meta-analysis included 33 groups with a total of 33 141 subjects, who had been recruited from the general population in 13 surveys and from occupational groups in 10 studies. In all but four studies the results were adjusted for age, and most studies took into account additional confounding factors. The association between blood pressure and blood lead was similar in both men and women. In the combined studies, a twofold increase in blood lead concentration was associated with a 1.0 mmHg rise in systolic pressure (confidence interval 0.4-1.6 mmHg; P = 0.002) and with a 0.6 mmHg increase in diastolic pressure (confidence interval 0.2-1.0 mmHg; P = 0.02). The association with systolic pressure strongly relied on the inclusion of a large study (n = 3851) in which women's blood pressure was measured at the end of pregnancy. The association with diastolic pressure was largely due to a population survey in the USA (n = 6289). There was no relationship across studies between the strength of the blood pressure-blood lead relationship and the mean blood lead concentration. The published evidence suggests that there can only be a weak positive association between blood pressure and lead exposure. Any such relationship may not be causal and is unlikely to entail any public-health implication in terms of hypertension-related complications. Nevertheless, these assumptions need to be confirmed in prospective population studies.