Researchers have found that bone loss occurs twice as fast among women living in areas with higher air pollution, particularly postmenopausal women, and that, for instance, living in these areas for just five years could be long enough to lower bone mineral density at the hip – the biggest risk factor for hip fractures, killing around one in three people.
For the study, the researchers scanned the bones of more than 9 000 women living in four different parts of the US. Each had a bone scan three times over a six-year period that was compared with the air they breathed.
On average, air pollution accounted for a doubling of the speed of bone loss, they reported in The Lancet.
In the US, 10m people are thought to have osteoporosis, of whom about 80% are women. The condition weakens bones and is linked to more than 2m fractures a year in the US, with a cost of more than $20bn annually. Only about 40% of these people regain full independence after their fracture.
In Britain, osteoporosis affects 3.8m people and the resulting fractures account for about 2% of total healthcare spending, reports The Guardian.
The latest study helps to explain earlier work by the same research group that looked at hospitalisation for fractures among more than 9m people in the eastern US.
Here the team found that particle pollution increased the number of incidents of people being admitted to hospital with fractures by 8% in their study group.
Importantly, these studies show effects at air pollution concentrations that are well below the current limits in the US and Europe, and well below the UK Government’s proposed limits for 2040.
Dr Diddier Prada, from the US study team at Columbia University’s Mailman School of Public Health, said: “The global population is getting older because of increased life expectancy and declining birth rates. We should identify, and eliminate, critical factors affecting human health during ageing. Postmenopausal women are susceptible to bone fractures and reductions in bone mineral density not just because of oestrogen reduction but from air pollution.
“Further action is needed to reduce pollution from diesel vehicles and wider fossil fuel use to protect public health.”
The researchers found the lumbar spine was most susceptible to air pollution-induced bone loss, and especially from nitrogen oxides. These are a group of pollutants including nitrogen dioxide, that breaches legal limits along many main roads in the UK and across Europe.
These breaches have persisted since the start of the century, exposing many people to high concentrations of nitrogen dioxide. This comes mainly from traffic, especially the large numbers of diesel vehicles that were manufactured to pass exhaust tests but produced much more pollution when used on our roads.
In the UK, a recent study of people living with more than one chronic illness found osteoporosis among the conditions linked to air pollution, and a further study found links between air pollution, lower bone density and increased fractures.
Research on the linkage between bone health and air pollution is an emerging field, including studies on people in rural China, but a consistent research approach is yet to emerge, making it hard to compare findings.
Dr Richard Abel from the faculty of medicine at Imperial College London, who was not involved in the US studies, said: “These studies reported that living in areas with high air pollution for just five years might be long enough to lower bone mineral density at the hip.
“This is worrying because low bone mineral density is the biggest risk factor for hip fractures, which kill around one in three people and disable one in three. The next important research step is to discover a physiological mechanism to confirm whether exposure to air pollution really does damage bone health.”
Study details
Air pollution and decreased bone mineral density among Women's Health Initiative participants
Diddier Prada, Carolyn Crandall, Allison Kupsco, Marianthi-Anna Kioumourtzoglou, James D. Stewart, Duanping Liao, et al.
Published in The Lancet on 14 February 2023
Summary
Background
Osteoporosis heavily affects postmenopausal women and is influenced by environmental exposures. Determining the impact of criteria air pollutants and their mixtures on bone mineral density (BMD) in postmenopausal women is an urgent priority.
Methods
We conducted a prospective observational study using data from the ethnically diverse Women's Health Initiative Study (WHI) (enrolment, September 1994–December 1998; data analysis, January 2020 to August 2022). We used log-normal, ordinary kriging to estimate daily mean concentrations of PM10, NO, NO2, and SO2 at participants' geocoded addresses (1-, 3-, and 5-year averages before BMD assessments). We measured whole-body, total hip, femoral neck, and lumbar spine BMD at enrolment and follow-up (Y1, Y3, Y6) via dual-energy X-ray absorptiometry. We estimated associations using multivariable linear and linear mixed-effects models and mixture effects using Bayesian kernel machine regression (BKMR) models.
Findings
In cross-sectional and longitudinal analyses, mean PM10, NO, NO2, and SO2 averaged over 1, 3, and 5 years before the visit were negatively associated with whole-body, total hip, femoral neck, and lumbar spine BMD. For example, lumbar spine BMD decreased 0.026 (95% CI: 0.016, 0.036) g/cm2/year per a 10% increase in 3-year mean NO2 concentration. BKMR suggested that nitrogen oxides exposure was inversely associated with whole-body and lumbar spine BMD.
Interpretation
In this cohort study, higher levels of air pollutants were associated with bone damage, particularly on lumbar spine, among postmenopausal women. These findings highlight nitrogen oxides exposure as a leading contributor to bone loss in postmenopausal women, expanding previous findings of air pollution-related bone damage.
The Guardian article – Air pollution ‘speeds up osteoporosis’ in postmenopausal women (Open access)
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