Long-term exposure to particulate matter increases cancer mortality

Long-term exposure to ambient fine particulate matter significantly increased risk for cancer mortality among elderly people in Hong Kong, according to study results.

Long-term exposure also significantly increased risk for death from all natural causes, as well as risk for death from several specific malignancies. These included cancers of the upper digestive tract and accessory organs in both men and women, lung cancer in men, and breast and genital cancers in women.

Particulate matter includes heavy metals or hydrocarbons produced by power generation, transportation and other sources.

“Long-term exposure to particulate matter has been associated with mortality mainly from cardiopulmonary causes and lung cancer, but there have been few studies showing an association with mortality from other cancers,” Thuan Quoc Thach, PhD, scientific officer at the school of public health at University of Hong Kong, said in a press release. “[We] suspected that these particulates could have an equivalent effect on cancers elsewhere in the body.”

Thach and colleagues evaluated health risks associated with long-term exposure to particulate matter with aerodynamic diameter less than 2.5 µm (PM_2.5).

The analysis included 66,820 people aged 65 years or older who lived in or near Hong Kong. Researchers recruited study participants from 1998 to 2001. Follow-up for mortality continued until 2011.

Thach and colleagues adjusted for smoking status and excluded deaths that occurred within 3 years of baseline to control for competing diseases. Researchers also accounted for the height of study participants’ residence above ground level.

The investigators measured PM_2.5 concentrations at fixed-site monitors, horizontal–vertical locations and satellites to estimate annual particulate matter concentrations at study participants’ residences.

The estimated PM_2.5 mean concentration in the baseline year at individual residential locations was 33.7 µg/m³ (range, 29.5-39.8).

During follow-up, 14,389 (21.5%) study participants died of natural causes (adjusted HR = 1.13; 95% CI, 1.08-1.19) and 4,531 (6.7%) participants died of malignant causes (adjusted HR = 1.22; 95% CI, 1.11-1.34).

Thach and colleagues used Cox regression to assess HR for cancer mortality per 10 µg/m³ of PM_2.5 exposure.

Results showed each 10 µg/m³ increase significantly increased risk for mortality from cancers of all digestive organs (HR = 1.22; 95% CI, 1.05-1.42), digestive accessory organs (HR = 1.35; 95% CI, 1.06-1.71) and the upper digestive tract (HR = 1.42; 95% CI, 1.06-1.89).

Increased exposure also appeared significantly associated with elevated risks for death from lung cancer among men (HR = 1.36; 95% CI, 1.05-1.77), as well as death from breast cancer (HR = 1.8; 95% CI, 1.26-2.55) or genital cancer (HR = 1.73; 95% CI, 1.17-2.54) among women.

The researchers acknowledged limitations of their study, including short follow-up, the role of genetic factors and metastasis, and the associations of multipollutant exposure or indoor pollution.

“This study is particularly timely in China, where compelling evidence is needed to support the pollution control policy to ameliorate the health damages associated with economic growth,” Thach and colleagues wrote.

However, the implications extend worldwide, the researchers said.

“PM_2.5 must be reduced as much and as fast as possible,” researcher Neil Thomas, MPhil, PhD, reader in epidemiology at Institute of Applied Health of the College of Medical and Dental Sciences at University of Birmingham in the United Kingdom, said in a press release. “Air pollution remains a clear, modifiable public health concern.” – by Nick Andrews

Disclosure: The researchers report no relevant financial disclosures.