Increases in stress hormone levels and other adverse metabolic changes accompany higher exposure to air pollution, Chinese researchers have found, while cutting indoor pollution levels appears to mitigate these effects.
Air pollution has been linked in epidemiological studies to increased risk of cardiovascular and metabolic diseases, but the mechanisms remain poorly understood. The new findings, published online Aug. 14 in Circulation, offer compelling evidence that air pollution may impact the central nervous system, and the hypothalamus-pituitary-adrenal axis especially (Circulation 2017 Aug 14;136:618-27).
The study design required that students spend as much time in their dorms as possible with the windows closed, though they could venture out for classes and exams. Fine particle concentration in the dorms treated by purifiers was 8.6 mcg per cubic meter during the study period, compared with a mean 101.4 outdoors. The researchers determined that the time-weighted average student exposure to fine particle pollutants was reduced by more than half when the dorm air was being purified, though average student exposure was estimated at 24 mcg per cubic meter at best. The World Health Organization considers levels below 10 mcg to be safe.
Students in untreated dorms had significant increases in cortisol, cortisone, epinephrine, norepinephrine, and biomarkers of oxidative stress at 9 days compared to those in treated ones. Glucose, insulin, measures of insulin resistance, amino acids, fatty acids, and lipids differed significantly between treatment assignments, and the untreated dorm groups also saw 2.61% higher systolic blood pressure (95% confidence interval [CI], 0.39-4.79).
Glucocorticoids are known to affect blood pressure, the investigators noted. Serum cortisol and cortisone levels were 1.3 and 1.2 times higher for the students in the sham-treated dorms, with each 10-mcg increase in pollutant exposure associated with a 7.8% increase in cortisol (95% CI, 4.75-10.91) and a nearly 3.8% increase in cortisone (95% CI, 1.84-5.71). Similar exposure-dependent increases were seen for norepinephrine, melatonin, phenylalanine, tyrosine, L-tryptophan and other compounds.
“To the best of our knowledge, this is the first study that used the untargeted metabolomics approach to investigate human global metabolic changes in relation to changes in ambient [air pollution] exposures,” the investigators wrote in their analysis, adding that the findings “provide insights into the potential mechanisms of the adverse health effects that have been found to be associated with [pollution] exposure.”
Mr. Li and Dr. Cai recommended the use of indoor air purification technology as a practical way to reduce harmful exposure, noting that the benefits of long-term use, particularly relating to cardiovascular and metabolic health, remain to be established.
The study was funded with grants from national and regional government agencies in China, and none of its authors declared conflicts of interest.