Air pollution worsens osteoporosis

Relation

Ranzani OT, Milà C, Kulkarni B, Kinra S, Ton C. Association of ambient and household air pollution with bone mineral content in adults in peri-urban southern India.JAMA network opened. 2020;3(1):e1918504.

Draft

This was a population-based cross-sectional analysis.

Participant

The analysis included 3,717 members of the Andhra Pradesh Children and Parents Study cohort recruited between 2009 and 2012 from 28 villages near Hyderabad, southern India. The average age was 35.7 years, and almost half of the participants (46%) were women.

Exposure measurements

Annual average ambient particulate matter air pollution less than 2.5 µm in aerodynamic diameter (PM2.5) and black carbon content (BC) at place of residence estimated by land use regression and self-reported biomass use for cooking

Target parameters

The primary outcome was bone mineral content (BMC), measured in grams, corrected for 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 present several possible mechanisms why particulate matter could affect bone mass. Perhaps most simply, 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 sequentially adjusted for potential confounders. Data analysis was conducted between April 2019 and July 2019.

Key insights

Ambient air pollution was associated with lower BMC. In fully adjusted models, PM2.5 was associated with lower spine BMC (mean difference -0.57 g per 3 μg/m³Increase in PM2.5) and hip (mean difference -0.13 g per 3 μg/m³increase in PM2.5). After confounder adjustment, PM2.5 exposure was also associated with lower bone mineral density in the spine (mean difference -0.011 g/cm²per 3 μg/m³increase in PM2.5) and hip (mean difference -0.004 g/cm²per 3 μg/m³increase in PM2.5). Black carbon exposure was associated with lower spine BMC (mean difference -1.13 g per 1 μg/m³Increase in BC) and hip (mean difference -0.35 g per 1 μg/m³). There was no association between biomass fuel use and spinal BMC.

Practice implications

There is already considerable evidence linking particulate matter air pollution to a variety of non-communicable diseases.¹Whether or not osteoporosis should be added to this list of diseases was unclear. Some studies have shown a connection between particulate matter exposure and lower bone density or fracture risk.^2.3Others don't.⁴One study found an increased risk of forearm fractures in older men, but not in younger women or men.⁵Another study reported an increase in hip fractures in older women exposed to gaseous air pollutants, but no significant effect of particulate matter.⁶Although studies to date have not produced consistent results, the idea that particulate matter may be associated with osteoporosis not only remains, but is now supported by the results of this current study by Ranzani et al.

The authors present several possible mechanisms why particulate matter could affect bone mass. Perhaps most simply, exposure increases systemic inflammation⁷and oxidative stress,⁸which then leads to increased bone loss.

A 2015 study reported faster bone turnover in children exposed to higher levels of particulate matter.⁹It seems reasonable to assume that this will also be the case in adults. It has also been suggested that higher levels of pollutants block exposure to ultraviolet light, which may affect calcium homeostasis by decreasing vitamin D production.¹⁰

Ranzani et al. reported that the association between particulate matter exposure and low bone mass was greater for the lumbar spine, which consists primarily of trabecular bone, than for the hip, which has a higher proportion of cortical bone. Trabecular bone appears to respond more strongly to oxidative stress from fine particles than cortical bone.¹¹

Whatever the cause, the link between particulate matter air pollution and osteoporosis appears to be growing stronger with this publication, and it is time we incorporate this air quality concern into our treatment protocols for at-risk patients or those with reduced bone mass.

Our list of chronic health problems related to particulate matter pollution continues to grow. Our late colleague Walter Crinnion's suggestion that getting patients to buy air filters could be the most important action they could take to improve their health seems increasingly prophetic as time goes on.