Blood lead-blood pressure relations: alcohol intake and hemoglobin as confounders

A cohort of 1,052 persons (504 men and 548 women) born in 1936 and residing in the Glostrup area, Denmark, underwent a comprehensive physical examination in 1976 at age 40 years, and 966 underwent a complete reexamination five years later. The examinations included blood lead concentration and blood pressure assessment under careful quality control. Complete blood lead and blood pressure data were available for 861 of these subjects (451 men and 410 women). The median blood lead levels were 13 and 9 micrograms/100 ml at age 40 years and 9 and 6 micrograms/100 ml at age 45 years in men and women, respectively. A slightly increased blood lead concentration was seen at age 40 years in women with a systolic blood pressure above 140 mmHg and/or a diastolic blood pressure above 90 mmHg. Systolic blood pressure in men and women and diastolic blood pressure in women correlated significantly with log blood lead at age 40 years but not at age 45 years, a doubling in blood lead being associated with an increase in blood pressure of 3 mmHg or less. Of nine potential confounders assessed, only blood hemoglobin and alleged alcohol intake were significantly associated with both blood lead and blood pressure. If one or both confounders were entered into a multiple regression analysis, all associations between blood lead and blood pressure became nonsignificant, in some cases with a negative regression coefficient. In addition, the blood lead:hemoglobin ratio was poorly associated with blood pressure, particularly in individuals with a low alcohol intake. Because both hemoglobin level and alcohol intake appear to be biologically plausible confounders, any independent effect of low-level lead exposure on blood pressure could not be determined.