We have long recognized that our environment has a significant impact on our general health. Air pollution is known to contribute to respiratory conditions, poor cardiovascular outcomes, and certain kinds of cancer.
It’s increasingly important to identify factors that might contribute to suboptimal bone density and associated fracture risk in the population as a whole, and particularly in older adults. Aging is associated with a higher risk for osteoporosis and fractures, with their attendant morbidity, but individuals differ in their extent of bone loss and risk for fractures.
Known factors affecting bone health include genetics, age, sex, nutrition, physical activity, and hormonal factors. Certain medications, diseases, and lifestyle choices – such as smoking and alcohol intake – can also have deleterious effects on bone.
More recently, researchers have started examining the impact of air pollution on bone health.
As we know, the degree of pollution varies greatly from one region to another and can potentially significantly affect life in many parts of the world. In fact, the World Health Organization indicates that 99% of the world’s population breathes air exceeding the WHO guideline limits for pollutants.
Air pollutants include particulate matter (PM) as well as gases, such as nitric oxide, nitrogen dioxide, ammonia, carbon monoxide, sulfur dioxide, ozone, and certain volatile organic compounds. Particulate pollutants include a variety of substances produced from mostly human activities (such as vehicle emissions, biofuel combustion, mining, agriculture, and manufacturing, and also forest fires). They are classified not by their composition, but by their size (for example, PM1.0, PM2.5, and PM10 indicate PM with a diameter < 1.0, 2.5, and 10 microns, respectively). The finer the particle, the more likely it is to cross into the systemic circulation from the respiratory tract, with the potential to induce oxidative, inflammatory, and other changes in the body.
Many studies report that air pollution is a risk factor for osteoporosis. Some have found associations of lower bone density, osteoporosis, and fracture risk with higher concentrations of PM1.0, PM2.5, or PM10, even after controlling for other factors that could affect bone health. Some researchers have reported that although they didn’t find a significant association between PM and bone health, they did find an association between distance from the freeway and bone health – thus, exposure to polycyclic aromatic hydrocarbons and black carbon from vehicle emissions needs to be studied as a contributor to fracture risk.
Importantly, a prospective, observational study from the Women’s Health Initiative (which included more than 9,000 ethnically diverse women from three sites in the United States) reported a significant negative impact of PM10, nitric oxide, nitrogen dioxide, and sulfur dioxide over 1, 3, and 5 years on bone density at multiple sites, and particularly at the lumbar spine, in both cross-sectional and longitudinal analyses after controlling for demographic and socioeconomic factors. This study reported that nitrogen dioxide exposure may be a key determinant of bone density at the lumbar spine and in the whole body. Similarly, other studies have reported associations between atmospheric nitrogen dioxide or sulfur dioxide and risk for osteoporotic fractures.