Low-level lead exposure, renal function and blood pressure.

The possible influence of low-level lead exposure on public health remains a matter of concern. The purpose of this article was to review the evidence that renal function and blood pressure may be affected at exposure levels encountered in the Belgian population. Moreover a meta-analysis explored whether the available studies in man would support a positive association between low-level lead exposure and hypertension. Renal function and lead exposures were studied in Belgium in a random population sample of 965 men and 1016 women (age range: 20 to 88 years). The mean (+/- standard deviation) creatinine clearance was 99 +/- 30 ml/min in men and 80 +/- 25 ml/min in women. In men the geometric mean blood lead concentration was 0.55 mumol/l with range from 0.11 to 3.5 mumol/l and in women 0.36 mumol/l with range from 0.08 to 2.9 mumol/l; the zinc protoporphyrin values in blood averaged 1.0 and 1.1 microgram/g haemoglobin, respectively. The creatinine clearance was negatively correlated with blood lead as well as zinc protoporphyrin values in men and women both before and after adjustments for age, body mass index and diuretic treatment. A tenfold rise in blood lead concentration was associated with a 10 to 13 ml/min reduction in the creatinine clearance. Serum beta 2-micro-globulin and zinc protopohyrin in both sexes, and serum creatinine and zinc protopohyrin in men were also significantly and positively correlated. Blood pressure was also measured in the Belgian population study. The sample, from which patients on antihypertensive treatment had been excluded, included 827 men and 821 women. Systolic/diastolic pressure averaged 131/77 mm Hg in men, and 124/74 mm Hg in women. After adjustment for significant covariates (age, body mass index, pulse rate, serum creatinine and serum calcium, and in women also contraceptive pill intake and menopause), systolic pressure was negatively correlated with blood lead in man (P < 0.05); the partial correlations with blood lead were not significant for systolic pressure in women, nor for diastolic pressure in both sexes. After excluding men exposed at work, the partial correlations between systolic and diastolic pressure and blood lead were negative (P < 0.05). In neither men nor women, there was a significant relation between blood pressure and the zinc protoporphyrin level in blood. A meta-analysis of 23 human studies included 33141 subjects, recruited from the general population in 13 surveys and from occupational groups in 10 studies. In all but 4 studies the results had been adjusted for age, and most studies also considered additional confounders. The association between blood pressure and blood lead was similar in the 2 sexes. In all 23 studies combined, a twofold increase in the blood lead concentration was associated with a 1.0 mm Hg rise in the systolic pressure (95% confidence interval [CI]: 0.4 to 1.6 mm Hg; P = 0.002) and with a 0.6 mm Hg increase in the diastolic pressure (CI: 0.2 to 1.0 mm Hg; P = 0.02). In conclusion, lead exposure may impair renal function in the population at large. However, the alternative hypothesis that renal impairment may lead to an increase in the blood lead concentration cannot yet be excluded with absolute certainty. On balance, the available evidence suggests that there can only be a weak positive association between blood pressure and lead exposure. The latter relationship, which is barely visible at the horizon of epidemiological observation, may not be causal in nature, and is likely to entail any public health implication in terms of hypertension-related complications.