Associations between bone lead and bone density in the Nurses Lead Study

Abstract

Background: Bone lead (Pb) is a marker of cumulative Pb exposure. Pb in bone may adversely affect both its cellular and structural components, but this association is not well understood. Methods: Study participants were Boston-area women from the Nurses’ Health Study [age 47-74 (mean 61)]. Pb was measured in the tibia and patella using k-X-ray Fluorescence. Bone Mineral Density (BMD) was assessed using dual-energy x-ray absorptiometry (DEXA) of the hip and spine. A subset of participants provided a second BMD measure 6 years after the initial visit. Results: 619 participants provided bone Pb and BMD measures. 163 participants returned for a second visit for longitudinal analysis. In cross sectional multivariable models adjusted for age, lifestyle, menopausal status and hormone replacement, a10 µg/g increase in patella Pb was associated with 1.2% (95% CI 0.3%, 2.1%) higher total hip BMD and 1.92% (95% CI 0.8%, 3.0%) higher total spine BMD. Similarly, a 10 µg/g increase in tibia Pb was associated with 1.1% (95% CI 0.004%, 2.2%) higher total hip BMD and 0.8% (95% CI -0.5%, 2.2%) higher spine BMD. Similar findings were observed for participants with a history of post-menopausal hormone use. Among women not using post-menopausal hormones, associations were attenuated and in some cases became negative, although not statistically significant. In longitudinal analysis, higher Pb was associated with a steeper decline in BMD, but results lacked precision. In subgroup analyses among women who had not used osteoporosis medications, each 10 µg/g increase in tibia Pb was associated with -0.08 (95% CI -0.2, -0.005) decline in BMD t-score. Conclusions: Our cross sectional results suggest that bone Pb may interfere with DEXA quantification of BMD (wherein Pb and calcium may be indistinguishable). This limitation does not apply to our longitudinal analyses where findings provide preliminary support for lead's hypothesized contribution to aging associated declines in BMD.