In the Journals

Air pollution’s effects comparable to obesity in increasing type 2 diabetes risk

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February 15, 2016

Mexican Americans exposed to short- and long-term air pollution were likely to have increased metabolic risk, including insulin resistance and elevated LDL cholesterol and fasting glucose levels, according to recent study findings.

“In this study of Mexican Americans, many of whom were young obese adults genetically related to women with a history of [gestational diabetes], exposure to ambient air pollutants was associated with a spectrum of adverse metabolic outcomes related to [type 2 diabetes] pathophysiology,” Zhanghua Chen, PhD, a postdoctoral scholar research associate at the Keck School of Medicine of the University of Southern California in Los Angeles, and colleagues wrote. “The magnitudes of effect from a 1-[standard deviation] difference of [fine particulate matter] on metabolic outcomes were similar compared with the impact of a 1-unit change in percent body fat or BMI on the same metabolic outcomes.”

Zhanghua Chen

Zhanghua Chen

Chen and colleagues analyzed data from participants in the BetaGene study (n = 1,023), a group of Mexican American women with confirmed gestational diabetes within the previous 5 years, as well as their siblings or cousins, recruited between 2002 and 2008 (mean age, 35 years; mean BMI, 29.7 kg/m²; 694 women). All participants had a fasting glucose of less than 7 mmol/L. Participants underwent a physical examination, 75 g oral glucose tolerance test, fasting blood sample for lipid measurements, DXA scan for body fat measurement and an insulin-modified frequently sampled IV glucose tolerance test to measure insulin sensitivity and beta-cell function, as well as food frequency and physical activity questionnaires.

Researchers measured ambient air quality between 2002 and 2008 using data from the U.S. Environmental Protection Agency’s air quality system, as well as the Southern California Children’s Health study; ozone (O₃) and nitrogen dioxide (NO₂) data were collected from federal reference method monitors. Air and traffic pollution exposures were assigned based on residential addresses provided by participants. Researchers used variance component models to analyze individual and multiple air pollutant associations with metabolic traits.

Short-term (up to 58 days cumulative lagged averages) exposure to fine particulate matter (PM2.5) was associated with lower insulin sensitivity and HDL-to-LDL cholesterol ratio and higher homeostasis model assessment of insulin resistance (HOMA-IR) and fasting glucose, insulin, total cholesterol and LDL levels (P .036 for all).

“As an example, a 1-[standard deviation] increase in 0 to 40 days’ PM2.5 was significantly associated with a 4.9% decrease in [insulin sensitivity],” the researchers wrote.

In assessing longer-term association patterns using monthly cumulative averages of air pollutant exposure, researchers found exposure to PM2.5 for 12 months was associated with higher HOMA-IR and fasting glucose and LDL levels (P .043 for all) after adjustment for age, sex, percent body fat and other variables.

The effects of short-term PM2.5 exposure on insulin sensitivity were largest among participants with obesity. Researchers found no statistically significant associations between traffic pollution and metabolic outcomes after adjustment.

 “Stricter controls of air pollution may help reduce the risk of developing type 2 diabetes,” Chen told Endocrine Today. “Studies aimed at understanding the mechanisms by which air pollution increases risk of type 2 diabetes are needed because it may help lead to targeted interventions among high risk populations.” – by Regina Schaffer

For more information:

Zhanghua Chen, PhD, can be reached at Southern California Environmental Health Sciences Center, Department of Preventive Medicine, University of Southern California Keck School of Medicine, 2001 N. Soto Street, Los Angeles, CA 90032; email: zhanghuc@usc.edu.

Disclosure: The researchers report no relevant financial disclosures.