Air Pollution and Weight Gain, Insulin Resistance and Metabolic Syndrome: Recent Findings

written by Sarah Howard
Coordinator of the Diabetes-Obesity Spectrum Working Group

Sarah HowardTwo studies published this month provided strong support for the idea that air pollution may cause weight gain, insulin resistance, and metabolic syndrome.

In the first study, pregnant rats exposed to Beijing’s air gained significantly more weight during pregnancy than those breathing filtered air. Their offspring (exposed pre- and postnatally) were also significantly heavier at 8 weeks of age.

In the second study, Mexican Americans living in Southern California exposed to ambient air pollutants had lower glucose tolerance, higher insulin resistance, and adverse blood lipid concentrations.  According to the authors, “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 [body mass index] BMI on the same metabolic outcomes.”

According to a Duke University press release about the first study:

 After only 19 days, the lungs and livers of pregnant rats exposed to the polluted air were heavier and showed increased tissue inflammation. These rats had 50 percent higher LDL cholesterol; 46 percent higher triglycerides; and 97 percent higher total cholesterol. Their insulin resistance level, a precursor of Type 2 diabetes, was higher than their clean air-breathing counterparts.

All of these measures support the study’s conclusion that air pollution exposure results in metabolic dysfunction, a precursor to obesity. Indeed, pollution-exposed rats were significantly heavier at the end of their pregnancy even though the rats in both groups were fed the same diet.

Similar results were shown in the rat offspring, which were kept in the same chambers as their mothers.

However, the results showed that the negative effects of air pollution were less pronounced after three weeks than they were at eight weeks, suggesting that long-term exposure may be needed to generate the continuous inflammatory and metabolic changes that ultimately increase body weight. At eight weeks old, female and male rats exposed to the pollution were 10 percent and 18 percent heavier, respectively, than those exposed to clean air.

This study received a lot of press coverage, for example:

airpollutionblog


First study:
Chronic exposure to air pollution particles increases the risk of obesity and metabolic syndrome: findings from a natural experiment in Beijing.
Wei Y, Zhang JJ, Li Z, Gow A, Chung KF, Hu M, Sun Z, Zeng L, Zhu T, Jia G, Li X, Duarte M, Tang X. FASEB J. 2016 Feb 18.

In a rodent model, we found that breathing Beijing’s highly polluted air resulted in weight gain and cardiorespiratory and metabolic dysfunction. Compared to those exposed to filtered air, pregnant rats exposed to unfiltered Beijing air were significantly heavier at the end of pregnancy. At 8 wk old, the offspring prenatally and postnatally exposed to unfiltered air were significantly heavier than those exposed to filtered air. In both rat dams and their offspring, after continuous exposure to unfiltered air we observed pronounced histologic evidence for both perivascular and peribronchial inflammation in the lungs, increased tissue and systemic oxidative stress, dyslipidemia, and an enhanced proinflammatory status of epididymal fat. Results suggest that TLR2/4-dependent inflammatory activation and lipid oxidation in the lung can spill over systemically, leading to metabolic dysfunction and weight gain.

Second study:
Ambient air pollutants have adverse effects on insulin and glucose homeostasis in Mexican Americans. Chen Z, Salam MT, Toledo-Corral C, Watanabe RM, Xiang AH, Buchanan TA, Habre R, Bastain TM, Lurmann F, Wilson JP, Trigo E, Gilliland FD. Diabetes Care. 2016 Feb 11.

Results: Short-term (up to 58 days cumulative lagged averages) exposure to PM2.5 was associated with lower insulin sensitivity and HDL-to-LDL cholesterol ratio and higher fasting glucose and insulin, HOMA-IR, total cholesterol, and LDL cholesterol (LDL-C) (all P ≤ 0.036). Annual average PM2.5 was associated with higher fasting glucose, HOMA-IR, and LDL-C (P ≤ 0.043). The effects of short-term PM2.5 exposure on insulin sensitivity were largest among obese participants. No statistically significant associations were found between traffic-related air pollution from freeways and metabolic outcomes.

An article about the second study:
Air pollution’s effects comparable to obesity in increasing type 2 diabetes risk, Healio Endocrine Today, Feb. 15, 2016, by Regina Schaffer.

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