Association of Fine Particulate Matter (PM2.5) and Wet-Bulb Globe Temperature (WBGT) with Osteoporosis Incidence: A Nationwide Prospective Cohort Study

<b>Background:</b> Fine particulate matter (PM2.5) negatively impacts human health, contributing to cardiovascular, kidney, and lung diseases, as well as cancer. Emerging evidence suggests that PM2.5 exposure may also impair bone density, increasing osteoporosis risk. Ambient temperature and humidity interact with PM2.5, potentially influencing disease onset. However, most studies focus on Western populations or low-pollution environments and lack long-term follow-up data. This study investigated the association between PM2.5 exposure, wet-bulb globe temperature (WBGT), and osteoporosis in a large Taiwanese cohort. <b>Methods:</b> Data from 19,981 participants in the Taiwan Biobank (TWB) were analyzed. PM2.5 exposure and WBGT were estimated using a Geo-AI-based ensemble mixed spatial model. Bone density was assessed using quantitative ultrasound, with osteoporosis defined as a T-score ≤ -2.5. Cox proportional hazards models assessed associations between PM2.5 exposure, WBGT, and osteoporosis risk. <b>Results:</b> Among participants (65% women, mean age 51 years, BMI 24 kg/m²), 1,303 (6.5%) developed osteoporosis during a 43-month follow-up. Incidence rates by PM2.5 quartiles were: 8.4% (1st), 5.7% (2nd), 5.3% (3rd), and 6.6% (4th). High PM2.5 quartile exposure was associated with a 1.66-fold increased osteoporosis risk (HR: 1.66, 95% CI: 1.43-1.92, p < 0.001). Log-transformed PM2.5 exposure also showed significant risk (HR: 1.73, 95% CI: 1.02-2.95, p = 0.043). Higher WBGT (26-27°C) independently increased osteoporosis risk (HR: 1.49, 95% CI: 1.33-1.66, p < 0.001). WBGT further amplified risk among individuals with lower PM2.5 exposure. <b>Conclusions:</b> PM2.5 exposure and elevated WBGT independently and interactively increased osteoporosis risk. Findings underscore the need for preventive strategies addressing environmental factors.