Association of air particulate pollution with bone loss over time and bone fracture risk: analysis of data from two independent studies

Abstract

Background: Air particulate matter (PM) is a ubiquitous environmental exposure associated with oxidation, inflammation, and age-related chronic disease. Whether PM is associated with loss of bone mineral density (BMD) and risk of bone fractures is undetermined.

Methods: We conducted two complementary studies of: (i) long-term PM <2.5 μm (PM_2.5) levels and osteoporosis-related fracture hospital admissions among 9.2 million Medicare enrollees of the Northeast/Mid-Atlantic United States between 2003-2010; (ii) long-term black carbon [BC] and PM_2.5 levels, serum calcium homeostasis biomarkers (parathyroid hormone, calcium, and 25-hydroxyvitamin D), and annualized BMD reduction over a 8-year follow-up of 692 middle-aged (46.7±12.3 yrs), low-income BACH/Bone cohort participants.

Findings: In the Medicare analysis, risk of bone fracture admissions at osteoporosis-related sites was greater in areas with higher PM_2.5 levels (Risk ratio [RR] 1.041, 95% Confidence Interval [CI], 1.030, 1.051). This risk was particularly high among low-income communities (RR 1.076; 95% CI, 1.052, 1.100). In the longitudinal BACH/Bone study, baseline BC and PM_2.5 levels were associated with lower serum PTH (Estimate for baseline one interquartile increase in 1-year average BC= -1.16, 95% CI -1.93, -0.38; Estimate for baseline one interquartile increase in 1-year average PM_2.5= -7.39; 95%CI -14.17, -0.61). BC level was associated with higher BMD loss over time at multiple anatomical sites, including femoral neck (-0.08%/year per one interquartile increase; 95% CI -0.14, -0.02%/year) and ultradistal radius (-0.06%/year per one interquartile increase; 95% CI -0.12, -0.01%/year).

Interpretation: Our results suggest that poor air quality is a modifiable risk factor for bone fractures and osteoporosis, especially in low-income communities.

Figure 1. Population and levels of fine air particulate pollution in the Northeast/Mid-Atlantic United States

Panel A: Medicare population by zip code. Panel B: Average PM_2.5 levels per zip code between 2003–2010.

Figure 2. Long-term exposure to PM_2.5 and risk of hospital admission for bone fractures

Panel A: Scatter plot of the multivariable-adjusted residuals from the standard regression model (not including PM_2.5) versus level of exposure to fine particulate matter <2.5 μm (PM_2.5). Panel B: Spline for the multivariable-adjusted association between PM_2.5 exposure and number of hospital admissions of Medicare enrollees per zip code, from 2003–2010. Panel C: Density plot of exposure to PM_2.5 in the Medicare analysis. Dotted line represents the primary annual PM_2.5 standard of 12 μg/m³ mandated by the U.S. Environmental Protection Agency.