Air pollution and risk of type 2 diabetes mellitus: A systematic review and meta-analysis

Aim: Whether exposure to relatively high levels of air pollution is associated with diabetes occurrence remains unclear. To assess and quantify the association between exposure to major air pollutants and risk of type 2 diabetes.

Methods: PubMed and EMBASE databases (through September 2013) were searched using a combination of terms related to exposure to gaseous (NO2 and NOx) or particulate matter pollutants (PM2.5, PM10 and PM10-2.5) and type 2 diabetes. Descriptive and quantitative information were extracted from selected studies. We used random-effects models meta-analysis to derive overall risk estimates per type of pollutant.

Results: We included ten studies (five cross-sectional and five prospective), assessing the effects of air pollutants on the occurrence of diabetes. In prospective investigations, the overall effect on diabetes occurrence was significant for both NO2 (adjusted hazard ratio [HR], 1.13; 95% confidence interval [95%CI], 1.01-1.22; p < 0.001; I2 = 36.4%, p-heterogeneity= 0.208) and PM2.5 (HR, 1.11; 95%CI, 1.03-1.20; p < 0.001; I2 = 0.0%, p-heterogeneity= 0.827). Odds ratios were reported by two cross-sectional studies which revealed similar associations between both NO2 and PM2.5 with type 2 diabetes. Across studies, risk estimates were generally adjusted for age, gender, body mass index and cigarette smoking.

Conclusions: Available evidence supports a prospective association of main air pollutants with an increased risk for type 2 diabetes. This finding may have implications for population-based strategies to reduce diabetes risk.


Alex’s Notes: Nature is a beautiful thing, and the outdoors and fresh air are often underappreciated. Yet, it is ironic that most people who do enjoy the great outdoors don’t give a second thought to air pollution. It is definitely not as large a problem in the U.S. as it is elsewhere (*cough* China), but living in cities does have its drawbacks. With the increasing rates of type-2 diabetes (T2DM), it only makes sense to look at every possible cause. Therefore, the authors decided to tackle the issue of air pollution and elude to any possible associations between the two variables.

Any cross-sectional, case-control, and cohort studies reporting a quantitative measure of the association between exposure to air pollution and risk of T2DM were included in the review, with a focus on gaseous pollutants (O3, CO, SO2, NO2 and NOx) and particulate matter pollutants (PM2.5, PM10 and PM10-2.5). Moreover, only human studies were allowed. For those curious about the pollutants, I summarized some information about them in the table below.


Human Sources

Health Effects

Environmental Effects


Secondary pollutant formed by chemical reaction of VOCs and NOx in the presence of sunlight.

Breathing problems, reduced lung function, asthma, irritates eyes, stuffy nose, reduces resistance to colds and infections, premature aging of lung tissue.

Damages crops, forests, and other vegetation; damages rubber, fabric, and other materials; smog reduces visibility.

Nitrogen Oxides (NOx)

Burning of gasoline, natural gas, coal, oil.

(Cars are a major source of NOx.)

Lung damage, respiratory illnesses, ozone (smog) effects.

Ozone (smog) effects; precursor of acid rain which damages trees, lakes, and soil; aerosols can reduce visibility.

Acid rain also causes buildings, statues, and monuments to deteriorate.

Carbon Monoxide (CO)

Burning of gasoline, natural gas, coal, oil.

Reduces ability of blood to bring oxygen to body cells and tissues.


Particulate Matter

Emitted as particles or formed through chemical reactions; burning of wood, diesel, and other fuels; industrial processes; agriculture (plowing, field burning); unpaved roads.

Eye, nose, and throat irritation; lung damage; bronchitis; cancer; early death.

Source of haze which reduces visibility.

Ashes, smoke, soot, and dust can dirty and discolor structures and property, including clothes and furniture.

Sulfur Dioxide (SO2)

Burning of coal and oil, especially high-sulfur coal; industrial processes (paper manufacturing, metal smelting).

Respiratory illness, breathing problems, may cause permanent damage to lungs.

Precursor of acid rain, which can damage trees, lakes, and soil; aerosols can reduce visibility.

Acid rain also causes buildings, statues, and monuments to deteriorate.

A total of ten studies met the inclusion criteria, of which half were cohort and half were cross-sectional. All studies were conducted in industrialized nations (US, Canada, & Europe), and the study participants totaled 385,395 with an age range of 21-75 years. The cohort studies had a follow-up length of 8-16 years.

“Two cohort studies suggested an association between particulate matter pollutants [12] and [23] and diabetes, while all three reports from cohort studies on NO2 exposure suggested a trend toward a positive association with diabetes risk [10][12] and [20].“

Regarding the cross-sectional studies, all but one found an association between increasing levels air pollution and the prevalence of diabetes. Additionally, some studies suggested a positive association for distances less than 100 meters to high density road traffic. After pooling the results for meta-analysis, the authors found a 13% & 11% increased risk for T2DM with every 10 μg/m3 increase in NO2 and PM2.5, respectively.

Curious about your city? Me too! I did a little digging and found the Air Quality Standards (AQI) below:

AQI Category

Index Values

Breakpoints (μg/m3)







Unhealthy for Sensitive Groups






Very Unhealthy






You can then look up your city from this website. For instance, looking at Bellevue, Washington – my home town – the AQI is 42, which tells me that I am probably right around the 10 μg/m3 for air pollutants, giving myself a 12% increased risk for diabetes. At moment of this writing, the five most polluted cities in the U.S. are in California with a range of 137 (~40 μg/m3) to 161 (~60 μg/m3), putting the residents at a 48-72% increased risk of diabetes! Wow. And for amusements sake, it appears that this area is in the top quartile for total diabetes mortality in California, as well as being in the top quartile for adults who are diagnosed with type-2 diabetes, which gives support to the notion that pollution may increase diabetes risk and I would speculate that it aggravates it as well.

I would apologize for getting somewhat off the topic of the study, but it is still relevant to our discussion, and I know you will be playing around with some of the links to see what pollution is like across the world. Enjoy!

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