National Coordinator of the Diabetes-Obesity Spectrum Working Group
Of course what you eat can affect your risk of diabetes and obesity, but how about what you breathe? Can air pollution influence the risk of diabetes and obesity? Surprisingly, it might.
Long-term exposure to traffic-related air pollution is associated with an increased risk of type 2 diabetes in a number of studies. For example, African-American women living in Los Angeles had a higher risk of diabetes if their homes were located in areas with higher traffic-related air pollution levels, after controlling for other diabetes risk factors such as age, body mass index, exercise, and family history (Coogan et al 2012). Adults in Denmark had an increased risk of diabetes when exposed to higher levels of the traffic-related air pollutant nitrogen dioxide (NO2)—expecially those who had a healthy lifestyle, were physically active, and did not smoke—factors that should be protective against type 2 diabetes (Andersen et al 2012). Elderly women in Germany had a higher risk of diabetes when living in areas of higher traffic-related air pollution, after adjusting for diabetes risk factors as well as several non-traffic-related sources of air pollution (Kramer et al 2010).
Cross-sectional studies also often show associations between diabetes and air pollution, although somewhat inconsistently (Brook et al 2008). A US-wide analysis found that people living in counties with higher levels of fine particulate matter (PM 2.5) have higher rates of diabetes, even when pollution levels were within EPA guidelines (Pearson et al. 2010). Even at low air pollution levels, Michigan adults had higher insulin resistance—a hallmark of type 2 diabetes—when exposed to PM 2.5 air pollutants for short time periods (Brook et al 2012). Associations between insulin resistance and air pollution are also found in countries with higher air pollution levels. Iranian children, for example, exposed to higher air pollution levels had higher insulin resistance as well (Kelishadi et al 2009).
Air pollution may also increase the risk of developing type 1 diabetes, an autoimmune disease that often develops during childhood. Southern Californian children exposed to higher levels of the air pollutants ozone and sulfate between birth and diabetes diagnosis had an increased risk of type 1 diabetes (Hathout et al 2006). In people who already have diabetes (of any type), air pollution may increase the risk of diabetes-related death (Raaschou-Nielsen et al. 2012).
Weight gain may entail more than the “calories-in, calories-out” model assumes. African-American or Hispanic women in New York City carried air pollution monitors while pregnant that measured their exposure to polycyclic aromatic hydrocarbons (PAHs), which are produced by burning fuels like gasoline and oil. Their children were more than twice as likely to be obese by age 7 if the mothers were exposed to higher PAH levels while pregnant, as compared to mothers with the lowest expsoure levels (Rundle et al. 2012).
These human studies are backed up by animal evidence. Adult male rats and mice exposed to small particulate matter (PM 2.5) air pollutants show increased insulin resistance (Yan et al 2011; Sun et al 2009). Mice exposed to air pollutants (PM 2.5) early in life have increased insulin resistance and inflammation, as well as fat tissue (Xu et al 2010). Pregnant mice exposed to diesel exhaust fumes have offspring that are more susceptible to weight gain later in life than those unexposed (Bolton et al 2012). Most of these animal studies found the effects using a high-fat diet, like the typical American diet.
We do not know how important air pollutants are in the development of diabetes and obesity, as compared to other risk factors. But even if air pollution only accounts for a small portion of the overall risk of diabetes and obesity, exposures are so widespread and diabetes and obesity are so common, that even small reductions in air pollutant levels may have significant public health benefits with respect to these conditions.
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Xu X, Yavar Z, Verdin M et al. 2010. Effect of early particulate air pollution exposure on obesity in mice: role of p47phox. Arterioscler.Thromb.Vasc.Biol. 30(12):2518-2527.
Many thanks for an excellent blog, informative and well referenced. Keep up the good work!
Dr Martin Hum, Editor Optimum Nutrition magazine, UK