Dietary calcium as a potential modifier of the relationship of lead burden to blood pressure

BACKGROUND: Cumulative lead burden and low dietary calcium have been independently associated with increased risk of hypertension. There is evidence of an interaction between these factors. We tested the hypothesis that dietary calcium intake modifies the relationship between lead burden and hypertension. METHODS: A total of 471 men from the Normative Aging Study were evaluated. Bone lead was assessed using a K-x-ray fluorescence instrument, and information on dietary calcium intake was obtained with a self-administered semiquantitative food frequency questionnaire. RESULTS: We categorized 259 subjects (55%) as having low calcium intake (≤800 mg/d) and 212 subjects (45%) as having higher calcium intake. In logistic regression models stratified by dietary calcium intake, tibia lead had a weak association with hypertension among subjects with low dietary calcium (odds ratio for 1-standard deviation increase in tibia lead = 1.30; 95% confidence interval = 0.97-1.74) but not in subjects with higher dietary calcium intake. Similarly, blood lead was associated with hypertension only in subjects with low calcium intake. We also found evidence of an interaction between dietary calcium intake and body mass index. CONCLUSIONS: High bone and blood lead increased the likelihood of hypertension, particularly among subjects with low dietary calcium intake. Dietary calcium may be helpful in prevention of hypertension induced by elevated lead burden.