Ambient, household air pollution independently drives CV death risk
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A model using satellite data to assess combined environmental exposures showed ambient fine particulate matter air pollution, along with household fuel use and ventilation, drove risk for CV death independent of other factors in rural Iran.
A special survival model developed to estimate the independent associations between eight environmental exposures and all-cause and CV mortality in a cohort of more than 50,000 people also showed proximity to traffic and distance to a center performing PCI were similarly associated with CV death risk, whereas factors such as nighttime light exposure, local population density and neighborhood socioeconomic status did not impact risk.
“Even though the risk is lower per person, in aggregate, the risk ends up being a significant burden of disease,” Michael B. Hadley, MD, MPH, a cardiology fellow and incoming assistant professor of medicine (cardiology) at the Icahn School of Medicine at Mount Sinai, told Healio. “Our study reinforces that, on the population level, these kinds of risk factors should not be overlooked. They end up a significant population burden of disease. Air pollution is the biggest, but we also showed proximity to traffic increases CV risk.”
Combined environmental risk factors
Hadley and colleagues collected data on individual and environmental risk factors for a multiethnic cohort of 50,045 adults aged 40 to 75 years who participated in the Golestan Cohort Study in northeastern Golestan, Iran (mean age, 52 years; 58% women). In both Iran and Golestan, CVD is the leading cause of death and disability, according to the researchers. Participants were interviewed by a physician and completed lifestyle questionnaires and a physical exam; each person was assigned a geocode based on residence location. The researchers developed exposure variables for eight prespecified environmental risk factors, including ambient fine particulate matter air pollution; household fuel use and ventilation; proximity to traffic; distance to a PCI center; socioeconomic environment; population density; local land use; and nighttime light exposure. The researchers developed a spatial survival model to estimate the independent associations between the environmental exposures and all-cause and CV mortality.
“Most studies that have looked at the impact of environmental risk factors for CVD have looked at them in isolation,” Hadley said in an interview. “It is easier to do that, but the problem is you lose the possibility of controlling for confounding by other environmental factors. For example, some researchers have looked at the impact of light at night disturbing circadian rhythm and the impact on CVD. They showed an association, but more recently, studies have shown that it is probably the air pollution driving that association; the light at night is just a surrogate marker for things like traffic. By looking at multiple variables simultaneously, we can hopefully reduce the possibility of unmeasured confounding.”
The researchers worked with a team with access to satellite databases to generate most of the eight risk factors, creating a map for how the risk changes over the study area of northeastern Iran.
“Based on these risk maps, you can look at where someone lives and assign them environmental exposures and risk, based on the location,” Hadley said.
The findings were published in PLoS One.
Air pollution and CV risk
Researchers found that several environmental factors demonstrated associations with mortality after adjusting for individual risk factors.
Ambient fine particulate matter air pollution predicted all-cause mortality, with an HR of 1.2 per g/m3 (95% CI 1.07-1.36), and CV mortality, with an HR of 1.17 (95% CI, 0.98-1.39). Compared with gas cooking, the use of biomass fuel use without a chimney was associated with all-cause mortality (HR = 1.23; 95% CI 0.99-1.53) and CV mortality (HR = 1.36; 95% CI, 0.99-1.87). Similarly, kerosene fuel use without chimney, compared with gas, predicted all-cause mortality (HR = 1.09; 95% CI, 0.97-1.23) and CV mortality (HR = 1.19; 95% CI, 1.01-1.41).
Additionally, each 10 km in distance to PCI center was associated with an increase in all-cause mortality (HR = 1.01; 95% CI, 1.004-1.022) and CV mortality (HR = 1.02; 95% CI, 1.004-1.031), whereas proximity to traffic was associated with all-cause mortality only (HR = 1.13; 95% CI, 1.01-1.27).
In a separate validation cohort, the multivariable model effectively predicted both all-cause mortality (area under the curve (AUC) = 0.76) and CV mortality (AUC = 0.81); population-attributable fractions demonstrated a high mortality burden attributable to environmental exposures.
“We have not reached a point yet where cardiologists necessarily need to bring this under their scope of practice,” Hadley said. “However, the world needs to move in that direction, particularly with climate change increasing the burden of all different types of environmental risk factors.”
Need for tailored interventions
For physicians practicing in areas where populations are highly affected by environmental risk factors, or for physicians who simply want to become more engaged, the approach depends on the risk factors and the patient, Hadley said.
“In a world of limited resources, you need to target individuals who are most susceptible and have the most to gain,” Hadley said. “For air pollution, for example, those with pre-existing coronary disease, children and older adults are more likely to develop CV outcomes from air pollution exposure. There is a whole suite of potential interventions that can be offered, depending on location and resources. If someone is living in California and they are exposed to wildfire smoke, that intervention may be different vs. someone who lives in New Delhi, India, exposed to commuter pollution during rush hour. One may need to temporarily stay inside with the windows closed, while the other may want to wear a respirator while driving. It comes down to these tailored conversations with patients.”
Forthcoming trials will help researchers create an evidence base to support the emerging research on environmental risk factors and CVD, Hadley said.
“For CVD, cardiologists have a very high standard for evidence, and we are accustomed to basing decisions on randomized trials,” Hadley said. “It is going to take another 10 years, I suspect, before we have the evidence base to say that putting on an N95 [mask] during a wildfire smoke event actually improves mortality.”
For more information:
Michael B. Hadley, MD, MPH, can be reached at michael.hadley@mountsinai.org.
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