The association of blood lead and blood pressure in population surveys.

Several reports from large population surveys have indicated that blood lead is positively related to blood pressure. We assessed this relation in 1,703 men (median blood lead = 83 micrograms per liter) and 1,661 women (median blood lead = 60 micrograms per liter), age 28 to 67 years, who participated in the first follow-up examination of the MONICA Augsburg cohort study in 1987-1988. Crude analyses confirmed a strong, positive association of blood lead concentrations with systolic and diastolic blood pressure. We identified age, body mass index, hematocrit, and alcohol consumption as the quantitatively most important confounders of this association. Adjustment for these variables, in particular for hematocrit and alcohol consumption, considerably reduced the magnitude of the blood lead effect on blood pressure. There were no indications for marked nonlinearity or threshold effects. After control of confounders, a difference of 100 micrograms per liter in blood lead levels, corresponding to rather extreme positions in the lower and upper end of the population blood lead distribution, related to estimated blood pressure increases of less than 3 mmHg. The appropriateness of treating hematocrit and alcohol consumption as confounders of the blood lead-blood pressure relation is discussed on the basis of current pathophysiologic concepts. We conclude that hematocrit should always be taken into account as a relevant confounder. On the other hand, the interrelation of alcohol consumption, blood lead, and blood pressure is presently not clearly understood; that is, its appropriate analytic handling cannot be determined. The consequences of these considerations on estimates of the blood lead effect on blood pressure may be both over- and underestimations.