Reference
Ranzani OT, Milà C, Kulkarni B, Kinra S, Tonne C. Association of ambient and household air pollution with bone mineral content among adults in peri-urban South India. JAMA Netw Open. 2020;3(1):e1918504.
Design
This was a population-based cross-sectional analysis.
Participants
The analysis included 3,717 members of the Andhra Pradesh Children and Parents Study cohort, who were recruited from 28 villages near Hyderabad, South India, during 2009 to 2012. Mean age was 35.7 years, and just under half of the participants (46%) were women.
Exposure Measurements
Annual mean ambient particulate matter air pollution less than 2.5 µm in aerodynamic diameter (PM2.5) and black carbon (BC) levels at the residence, estimated by land-use regression and self-reported use of biomass cooking fuel
Outcome Measures
The primary outcome was bone mineral content (BMC) measured in grams, corrected by bone area at the lumbar spine and left hip, as measured by dual-energy X-ray absorptiometry (DEXA). A secondary outcome was bone mineral density measured in grams per square centimeter.
The authors put forth several possible mechanisms why fine particulates might affect bone mass. Perhaps the simplest is that exposure increases systemic inflammation and oxidative stress, which then leads to increased bone loss.
Separate linear mixed models were fitted with nested random intercepts (household within villages) for each exposure-outcome pair and were sequentially adjusted for potential confounders. Data analysis was conducted between April 2019 and July 2019.
Key Findings
Ambient air pollution was associated with lower BMC. In fully adjusted models, PM2.5 was associated with lower BMC in the spine (mean difference, –0.57 g per 3 μg/m3 increase in PM2.5) and hip (mean difference, –0.13 g per 3 μg/m3 increase in PM2.5). After confounder adjustment, exposure to PM2.5 was also associated with lower bone mineral density in the spine (mean difference, –0.011 g/cm2 per 3 μg/m3 increase in PM2.5) and hip (mean difference, –0.004 g/cm2 per 3 μg/m3 increase in PM2.5). Exposure to black carbon was associated with lower BMC in the spine (mean difference, –1.13 g per 1 μg/m3 increase in BC) and hip (mean difference, –0.35 g per 1 μg/m3). There was no association between biomass fuel use and spine BMC.
Practice Implications
There is already a substantial body of evidence linking fine particulate air pollution to a wide variety of noncommunicable diseases.1 Whether or not osteoporosis should be added to this list of diseases has been unclear. Some studies have shown an association between fine particulate exposure and lower bone density or risk of fracture.2,3 Others have not.4 One study found an increase in forearm fracture risk in older men but not younger women or men.5 Another study reported an increase in hip fractures in older women exposed to gaseous air pollutants but no significant effect from fine particulates.6 Though the studies to date have not produced consistent results, the idea that fine particulates might be associated with osteoporosis not only remains but now is reinforced by the results of this current study by Ranzani et al.
The authors put forth several possible mechanisms why fine particulates might affect bone mass. Perhaps the simplest is that exposure increases systemic inflammation7 and oxidative stress,8 which then leads to increased bone loss.
A 2015 paper reported faster bone turnover in children exposed to higher levels of fine particulates.9 It seems reasonable to assume the same will occur in adults. It’s also been suggested that higher levels of pollution block ultraviolet-light exposure, which may affect calcium homeostasis by lowering vitamin D production.10
Ranzani et al reported that the association between fine particulate exposure and low bone mass was greater for the lumbar spine, which is mainly composed of trabecular bone, than for the hip, which has a higher proportion of cortical bone. Trabecular bone apparently is more responsive to oxidative stress from fine particulates than cortical bone is.11
Whatever the cause, the link between fine particulate air pollution and osteoporosis is looking stronger with this publication, and it is time we incorporate this concern about air quality into our treatment protocols for patients at risk or suffering from decreased bone mass.
Our list of chronic health conditions associated with fine particulate exposure continues to lengthen. The suggestion made by our late colleague Walter Crinnion that getting patients to purchase air filters might be the single most important intervention they could make to improve their health seems more prophetic as time goes on.
