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In a recent study published in the Environment International Journal, researchers discussed the relationship between long-term exposure to air pollution and its impact on cardiometabolic health markers.

Study: Long-term air pollution exposure and markers of cardiometabolic health in the National Longitudinal Study of Adolescent to Adult Health (Add Health) Study. Image Credit: BalazsVekony/Shutterstock.com

Background

Exposure to air pollution is linked to an increased risk of cardiovascular illness and death. Limited research has investigated the link between prolonged exposure to air pollution and cardiovascular health indicators in young adults, despite the possibility that early-life exposure to air pollution could contribute to the development of cardiovascular disease risk factors.

Several studies have shown that exposure to air pollutants is linked to risk factors for early signs of cardiovascular disease, which can appear many years before the onset of more severe symptoms.

About the study

In the present study, researchers analyzed the relationship of air pollution exposure with six cardiometabolic health markers, including hyperlipidemia, hypertension, penicillin allergy vomit diabetes, obesity, C-reactive protein (CRP), and an estimate of metabolic syndrome.

The team obtained data from the National Longitudinal Study of Adolescent to Adult Health, a nationally representative group of adolescents in grades seven to 12 in the 1994-95 school year.

A probability sample of over 20,000 adolescents was selected for in-home interviews during Wave I (WI) from 1994 to 1995. The cohort underwent four follow-up interviews: WII in 1996, WIII between 2001 and 2002, WIV between 2008 and 2009, and WV between 2016 and 2018. Across waves, response rates varied from 72% to 90%.

The study cohort included WI individuals who had also participated in the WIII and WIV, were geocoded, was residents of the continental United States, and had non-missing information related to critical covariates such as sex, age, and race/ethnicity.

The study analyzed biological and clinical data obtained at Wave IV to assess cardiometabolic health markers. This included systolic and diastolic blood pressure, body mass index (BMI), lipid panels, diabetes indicators, and C-reactive protein concentrations to estimate inflammation.

At Wave IV, the six markers of cardiometabolic health were analyzed. The Fused Air Quality Surface using Downscaling (FAQSD) files generated air pollution exposure estimates. The FAQSD files provide daily forecasts for the 24-hour average PM2.5 levels and eight-hour maximum ozone (O3) levels at 2010 US Census tract centroids.

Results

The average age of Wave IV Add Health participants was 28 years old, with almost 53% of the sample being female. Approximately 66% of the model consisted of Non-Hispanic White participants.

High inflammation and obesity were the most prevalent cardiometabolic health outcomes, with rates of 38.7% and 37.8%, respectively. This was followed by hypertension with 26.1% and metabolic syndrome with 20.7% prevalence rates.

The team noted that non-Hispanic White and non-Hispanic Black individuals displayed the highest O3 exposure levels, while other racial or ethnic groups had lower O3 exposure levels.

Furthermore, the study found that exposure to O3 from 2002-2007 was linked to higher chances of hypertension, diabetes, obesity, and metabolic syndrome after adjusting for race/ethnicity, age, and sex using generalized estimating equations (GEEs).

Elevated odds of hypertension were associated with 2002-07 PM2.5 exposure in models after adjustment for age, race/ethnicity, and sex.

The study found links between exposure to O3 and health issues such as hypertension, diabetes, obesity, inflammation, and metabolic syndrome. Additionally, exposure to PM2.5 was associated with hypertension. Individuals were categorized into low and high exposure groups for PM2.5, depending on their average 2002-07 PM2.5 levels.

In a sample of 11,259 individuals, 6,905 were exposed to PM2.5 levels of at least 12 μg/m3, while the remaining 4,354 were exposed to PM2.5 levels of less than 12 μg/m3 from 2002-07. No individuals in the dataset had O3 exposure ≥ 70 ppb, the National Ambient Air Quality Standard for O3 between 2002-07.

For every one-unit increase in O3 exposure, there was a 0.35% rise in BMI, a 0.10% elevation in HbA1c, and a 1.1% boost in hsCRP. The study found no significant associations between PM2.5 exposure and changes in BMI, HbA1c, and hsCRP levels.

Specifically, a one-unit rise in PM2.5 exposure was related to a -0.22% difference in BMI, a -0.13% difference in HbA1c, and a 0.11% difference in hs-CRP.

Conclusion

The study findings showed that exposure to O3 between 2002 and 2007 was linked to an increased likelihood of hypertension, diabetes, obesity, and metabolic syndrome.

A two-year lagged period between 2006 and 2007 of O3 exposure showed similar results, with increased chances of diabetes, obesity, inflammation, and metabolic syndrome.

Longitudinal studies that cover a wide range of ages include repeated biological analysis, and accurately estimating environmental exposures during critical development spans would be helpful in future research.

This would help to determine how long-term air pollution exposure affects cardiometabolic and cardiovascular disease risks over a person's lifetime.

Written by

Bhavana Kunkalikar

Bhavana Kunkalikar is a medical writer based in Goa, India. Her academic background is in Pharmaceutical sciences and she holds a Bachelor's degree in Pharmacy. Her educational background allowed her to foster an interest in anatomical and physiological sciences. Her college project work based on ‘The manifestations and causes of sickle cell anemia’ formed the stepping stone to a life-long fascination with human pathophysiology.