Some of the effects of air pollution on health are well documented – lung cancer, stroke, respiratory diseases, and a long etcetera – but for others there is less scientific evidence. Such is the case of bone health: there are only a few studies and results are inconclusive. Now, a study in India led by the Barcelona Institute for Global Health (ISGlobal), an institution supported by “la Caixa,” has found an association between exposure to air pollution and poor bone health.
Osteoporosis is a disease in which the density and quality of the bone is reduced. Globally, it is responsible for a substantial burden of disease and its prevalence is expected to increase due to ageing of the population.
The study performed by the CHAI Project, led by ISGlobal, analysed the association between air pollution and bone health in over 3,700 people from 28 villages outside the city of Hyberabad, in southern India.
The authors used a locally-developed model to estimate outdoor exposure at residence to air pollution by fine particulate matter (suspended particles with a diameter of 2.5mm or less) and black carbon. The participants also filled a questionnaire on the type of fuel used for cooking. The authors linked this information with bone health assessed using a special type of radiography that measures bone density, called dual-energy x-ray absorptiometry, and measured bone mass at the lumbar spine and the left hip.
The results showed that exposure to ambient air pollution, particularly to fine particles, was associated with lower levels of bone mass. No correlation was found with use of biomass fuel for cooking.
“This study contributes to the limited and inconclusive literature on air pollution and bone health,” explains Otavio T Ranzani, ISGlobal researcher and first author of the study. Regarding the possible mechanisms underlying this association, he says “inhalation of polluting particles could lead to bone mass loss through the oxidative stress and inflammation caused by air pollution.”
Annual average exposure to ambient PM2.5 was 32.8mg/m3, far above the maximum levels recommended by the World Health Organisation (10mg/m3). 58% of participants used biomass fuel for cooking.
“Our findings add to a growing body of evidence that indicates that particulate air pollution is relevant for bone health across a wide range of air pollution levels, including levels found in high income and low-and medium income countries” says Cathryn Tonne, coordinator of the study and of the CHAI project. “
Importance: Air pollution is a major threat to global health. Osteoporosis is responsible for a substantial burden of disease globally and is expected to increase in prevalence because of population aging. Few studies have investigated the association between air pollution and bone health, and their findings were inconclusive.
Objective: To quantify the association between ambient and household air pollution and bone mass in a sample of the general population in peri-urban India.
Design, Setting, and Participants: This was a population-based cross-sectional analysis of the Andhra Pradesh Children and Parents Study cohort, which recruited participants from 28 villages near Hyderabad, South India, during 2009 to 2012. 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.
Exposures: 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.
Main Outcomes and 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. The secondary outcome was bone mineral density measured in grams per centimetres squared.
Results: A total of 3717 participants were analyzed (mean [SD] age, 35.7 [14.0] years; 1711 [46.0%] women). The annual mean (SD) PM2.5 exposure was 32.8 (2.5) μg/m3, and the annual mean (SD) BC exposure was 2.5 (0.2) μg/m3; 57.8% of participants used biomass cooking fuels. 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; 95% CI, −1.06 to −0.07 g per 3 μg/m3 increase in PM2.5) and hip (mean difference, −0.13 g per 3 μg/m3 increase in PM2.5; 95% CI, −0.3 to 0.03 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; 95% CI, −0.021 to 0 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; 95% CI, −0.008 to 0.001 g/cm2 per 3 μg/m3 increase in PM2.5). Exposure to BC was associated with lower BMC in the spine (mean difference, −1.13 g per 1 μg/m3 increase in BC; 95% CI, −2.81 to 0.54 g per 1 μg/m3 increase in BC) and hip (mean difference, −0.35 g per 1 μg/m3 increase in BC; 95% CI, −0.96 to 0.25 g per 1 μg/m3 increase in BC), although the confidence intervals were wider. There was no association between biomass fuel use and spine BMC (mean difference, 0.12 g; 95% CI, −0.45 to 0.68 g).
Conclusions and Relevance: In a cross-sectional analysis of a population-based cohort, ambient air pollution was associated with lower BMC in a young adult population in a peri-urban area of South India.
Otavio T Ranzani, Carles Milà, Bharati Kulkarni, Sanjay Kinra, Cathryn Tonne