Prior studies have revealed associations of current lead exposure (blood lead) and past lead exposure (bone lead) with risks of hypertension and elevated blood pressure. The authors examined the effects of blood and bone lead on hypertension and elevated blood pressure in the third trimester and postpartum among 1,006 women enrolled in Los Angeles prenatal care clinics between 1995 and 2001. The authors measured bone lead concentration by K-shell x-ray fluorescence in the tibia (mean = 8.0 micro g/g (standard deviation (SD) 11.4)) and calcaneus (heel) (mean = 10.7 micro g/g (SD 11.9)). Geometric mean prenatal and postnatal blood lead levels were 1.9 micro g/dl (geometric SD +3.6/-1.0) and 2.3 micro g/dl (geometric SD +4.3/-1.2), respectively. For each 10- micro g/g increase in calcaneus bone lead level, the odds ratio for third-trimester hypertension (systolic blood pressure > or =140 mmHg or diastolic blood pressure > or =90 mmHg) was 1.86 (95% confidence interval (CI): 1.04, 3.32). In normotensive subjects, each 10- micro g/g increase in calcaneus bone lead level was associated with a 0.70-mmHg (95% CI: 0.04, 1.36) increase in third-trimester systolic blood pressure and a 0.54-mmHg (95% CI: 0.01, 1.08) increase in diastolic blood pressure. Tibia bone lead concentration was not related to hypertension or elevated blood pressure either in the third trimester or postpartum, nor was calcaneus bone lead related to postpartum hypertension or elevated blood pressure. Past lead exposure influences hypertension and elevated blood pressure during pregnancy. Controlling blood pressure may require reduction of lead exposure long before pregnancy.

Twenty-five years of public health efforts produced a striking reduction in lead exposure; the blood lead average in the United States has decreased to less than 20% of levels measured in the 1970s. However, poor minority groups that live in large urban centers are still at high risk for elevated lead levels. In this study, our data showed that pregnant immigrants (n = 1,428) who live in South Central Los Angeles--one of the most economically depressed regions of California--have significantly higher (p < .0001) blood lead levels (geometric mean = 2.3 microg/dl [0.11 micromol/l]) than 504 pregnant nonimmigrants (geometric mean = 1.9 microg/dl [0.09 micromol/l]). The most important factors associated with lower blood lead levels in both groups were younger age; more-recent date of blood sampling (i.e., decreasing secular trend); and blood sampling in mid-autumn, instead of mid-spring (i.e., seasonal trend). Blood lead levels of immigrants were strongly dependent on time elapsed since immigration to the United States; each natural log increase in years of residence was associated with an approximately 19% decrease in blood lead levels. Although blood lead means for both groups were almost the same as the estimated national average, 25 of the 30 cases of elevated blood lead (i.e., > or = 10 microg/dl [0.48 micromol/l) occurred in the immigrant group. The odds ratio (95% confidence intervals within parentheses) for having elevated blood lead levels (a) was 9.3 (1.9, 45.8) if the immigrant engaged in pica; (b) was 3.8 (1.4, 10.5) if the immigrant had low dietary calcium intake during pregnancy; and (c) was .65 (.43, .98) for every natural log unit increase of years of residence in the United States. The control of pica and dietary calcium intake may offer a means of reducing lead exposure in immigrants.

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In many studies in which the relationship between blood pressure and blood lead level has been examined, investigators have found significant--but small--associations. There was only one previous report of a significant association of blood lead with blood pressure in pregnant women. We measured blood lead level and sitting blood pressure of 1,627 women in their third trimester of pregnancy. We eliminated subjects with known causes of hypertension. Most women (98.4%) were normotensive. We controlled for body mass index, age, and stress--among other factors--and constructed multiple-regression models of lead association with diastolic and systolic blood pressures. Immigrants (73% of total) had significantly higher blood lead levels and different blood pressures than nonimmigrants, suggesting that analysis be stratified by "immigrant, nonimmigrant" status. Positive relationships between blood lead level and blood pressure were found only for immigrants (p < or = .001). From the 5th to 95th blood-lead percentiles (0.9-6.2 microg/dl) in immigrants, systolic blood pressure increased 2.8 mm Hg, and diastolic blood pressure increased 2.4 mm Hg. Higher prior lead exposure of immigrants (97.7% from Latin countries) than nonimmigrants might explain the differential effect of these low levels of blood lead on blood pressure in nonimmigrants. Perhaps some immigrants are at higher risk than nonimmigrants for lead-associated elevated blood pressure during pregnancy, despite blood lead levels within the currently considered acceptable range.

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