The relationship of blood lead and dietary calcium to blood pressure in the normative aging study

Abstract

Background. Previous studies have demonstrated a positive relationship between elevated blood lead (BPb) and blood pressure (BP), but few have additionally examined the role of dietary calcium. Methods. The cross-sectional relationship between BPb and BP and the possible protective influence of increased dietary calcium on that relationship was examined among 798 male participants in the Normative Aging Study (NAS), a cohort of older men with relatively low BPb levels. Results. The age range of these subjects was 43-93 years (mean = 66.1, SD = 7.4 years) and blood lead concentrations ranged from 0.5 to 35 mcg/dl (median = 5.6 mcg/dl). For the cohort overall, neither In blood lead nor dietary calcium were significantly correlated with BP. In multivariate linear regression analyses that adjusted for age, body mass index, dietary calcium intake (adjusted for total calorie intake), alcohol intake, sitting heart rate, kilocalories/week expended in exercise, haematocrit, and smoking status, a unit increase in In BPb predicted an increase of 1.2 mmHg diastolic blood pressure (DBP) (95% Cl : 0.11, 2.2; P = 0.03). Adjusted calcium intake of 800 mg/day predicted a decrease of 3.2 mmHg systolic blood pressure (SBP) (95% Cl :-5.6, -0.24, P = 0.03). There was no evidence of an interaction between dietary calcium intake and blood lead on BP. When the analyses were restricted to those men ≤ 74 years old, a unit increase in In BPb predicted an increase of 1.6 mmHg DBP (n = 681; 95% Cl :0.42, 2.7; P= 0.007), However, when men on antihypertensive medication (AHM) were excluded from the analyses, In BPb was not significantly associated with increased: DBP nor was adjusted calcium significantly associated with SBP. Conclusions. The study did support the hypothesis that increased BPb was associated with increased DBP in a cohort of older men with low blood lead, but there was no evidence of interaction between BPb and dietary calcium on BP. However, the relationship between increased BPb and DBP did not hold when those on anti-hypertensive medications were excluded.