Influence of bone resorption on the mobilization of lead from bone among middle-aged and elderly men: The normative aging study

Bone stores of lead accrued from environmental exposures and found in most of the general population have recently been linked to the development of h ypertension, cognitive decrements, and adverse reproductive outcomes. The s keleton is the major endogenous source of lead in circulating blood, partic ularly under conditions of accelerated bone turnover and mineral loss, such as during pregnancy and in postmenopausal osteoporosis. We studied the inf luence of bone resorption rate on the release of lead from bone in 333 men, predominantly white, middle-aged and elderly (mostly retired) from the Bos ton area. We evaluated bone resorption by measuring crosslinked N-telopepti des of type I collagen (NTx) in 24-hr urine samples with an enzyme-linked i mmunosorbent assay. We used K-X-ray fluorescence to measure lead content in cortical (tibia) and trabecular (patella) bone; we used graphite furnace a tomic absorption spectroscopy and inductively coupled plasma mass spectrosc opy to measure lead in blood and urine, respectively. After adjustment for age and creatinine clearance, the positive relation of patella lead to urin ary lead was stronger among subjects in the upper two NTx tertiles (beta fo r patella lead greater than or equal to 0.015) than in the lowest NTx terti le (beta for patella lead = 0.008; overall p-value for interactions = 0.06) . In contrast, we found no statistically significant influence of NTx terti le on the relationship of blood lead to urinary lead. As expected, the magn itude of the relationship of bone lead to urinary lead diminished after adj ustment for blood lead. Nevertheless, the pattern of the relationships of b one lead to urinary lead across NTx tertiles remained unchanged. Furthermor e, after adjustment for age, the relation of patella lead to blood lead was significantly stronger in the upper two NTx tertiles (beta for patella lea d greater than or equal to 0.125) than in the lowest NTx tertile (beta for patella lead = 0.072). The results provide evidence that bone resorption in fluences the release of bone lead stores (particularly patella lead) into t he circulation.