Environmental Factor, July 2010, National Institute of Environmental Health Sciences
Pollution Linked to Severity of Sleep-Disordered Breathing
By Negin Martin
In addition to restless nights and increased daytime sleepiness, sleep-disordered breathing (SDB) is linked to pulmonary, cardiovascular, and autonomic nervous system dysfunction. A new study led by investigators at the Harvard School of Public Health (HSPH) and funded in part by NIEHS (http://tools.niehs.nih.gov/portfolio/sc/detail.cfm?appl_id=7665543) found the first link between air pollution exposure and SDB, a known cause of cardiovascular disorders.
Collaborative effort among statisticians, physicians, and epidemiologists
The results (http://www.ncbi.nlm.nih.gov/pubmed/20508218) were published ahead of print in the American Journal of Respiratory and Critical Care Medicine. The lead author, biostatistician Antonella Zanobetti, Ph.D. (http://www.hsph.harvard.edu/research/antonella-zanobetti/) , is a senior research scientist in the Department of Environmental Health at the HSPH, who applies her expertise to analyzing epidemiological data linking pollution to morbidity and mortality. Zanobetti's collaborators, second author Susan Redline, M.D. (http://www.uhhospitals.org/tabid/1709/phyID/1117/Default.aspx) , from the Division of Sleep Medicine at Case Western Reserve University, and Harvard University Professor Diane Gold, M.D. (http://www.channing.harvard.edu/gold.htm) , the principal investigator on the study, are physicians dedicated to uncovering the effects of environment on human health. The group used data from the Sleep Heart Health Study (SHHS) and U.S. Environmental Protection Agency (EPA) air pollution monitoring results to draw conclusions for their research.
In a Brigham and Women's Hospital press release (http://www.brighamandwomens.org/Pressreleases/PressRelease.aspx?PageID=689) June 14, Zanobetti said of the findings, "We found novel evidence for pollution and temperature effects on sleep-disordered breathing. ... Increases in apnea or hypopnea... were associated with increases in short-term temperature over all seasons, and with increases in particle pollution levels in the summer months."
SDB is a silent killer
According to the researchers, abnormalities of breathing pattern during sleep often go unnoticed. SDB affects approximately 17 percent of U.S. adults and the percentage may be higher in poor urban areas, making the condition a significant public health problem.
The most common SDB disorder is the obstructive sleep apnea (OSA), which is total or partial collapse of the pharyngeal airways during sleep. OSA episodes may repeat over the course of the night and are only relieved by sleep arousal or waking up. SDB contributes to hypoxemia - reduced oxygen levels in blood - and respiratory acidosis. Many individuals afflicted with SDB are unaware of their condition and remain undiagnosed.
The study analyzed data from a large cohort
Over 6000 adults over the age of 39 were recruited for the SHHS cohort study on the health consequences of SDB. The subjects included individuals from major urban cities - Phoenix, Tucson, Sacramento, Framingham, Mass., Minneapolis, New York, and Pittsburgh. The comprehensive study included multiple health readings to determine oxygen levels, brain activity, quality of breathing, movement during sleep, and ambient environment.
Researchers defined an SDB episode as a decrease in chest movement amplitude of less than 75 percent (for apnea) and less than 30 percent (for hypopnea) that lasted at least 10 seconds and resulted in decreased airflow. The frequency of episodes was compared to the air quality data from EPA. Levels of particulate matter with diameter less than 10 micrograms (PM10) - mostly associated with traffic - determined the pollution exposure. Data was analyzed using linear regression models that took into account average temperature and season as well as potential SDB predictors such as age, body mass index, gender, education, smoking, and drinking habits.
Seasonal and temperature variation affects symptoms
During summer months, short-term changes in levels of PM10 pollution were associated with increased respiratory disturbances and sleep inefficiencies. Elevated PM10 levels also correlated with an increase in the amount of time that volunteers' blood oxygen saturation levels fell below 90 percent. Populations with these types of SDB episodes are more prone to cardiovascular morbidity.
Researchers also discovered that short-term temperature increases were coupled to higher incidence of apnea and hypopnea throughout the year.
Zanobetti and colleagues hypothesized that particulate matter in pollution may increase SDB by influencing the central nervous system and the upper airways. Air pollutants also contain allergens that could induce inflammation and trigger an allergic response contributing to SDB.
The study lends strength to the argument that reduction in pollution exposure may lower cardiovascular risk by reducing the frequency and severity of SDB.
Citation: Zanobetti A, Redline S, Schwartz J, Rosen D, Patel S, O'Connor GT, et al. (http://www.ncbi.nlm.nih.gov/pubmed/20508218) 2010. Associations of PM10 with Sleep and Sleep-disordered Breathing in Adults from Seven U.S. Urban Areas. Am J Respir Crit Care Med. Epub ahead of print. doi:10.1164/rccm.200912-1797OC
(Negin Martin, Ph.D., is a biologist in the NIEHS Laboratory of Neurobiology Viral Vector Core Facility and a 2009 Science Communication Fellow with Environmental Health Sciences. She recently completed a postdoctoral fellowship with the NIEHS Membrane Signaling Group.)