Environmental Factor, January 2008, National Institute of Environmental Health Sciences
Higher BMI Worsens Ozone Effect
By Robin Mackar
A new study published in Inhalation Toxicology and co-authored by two NIEHS researchers, Stephanie London, M.D., and Grace Kissling, Ph.D., provides the first evidence that people with higher body mass index (BMI) may have a greater response to ozone exposure than leaner people. Ozone is formed in the atmosphere in the presence of sunlight from pollutants emitted from vehicles and other sources.
Researchers at the National Institute of Environmental Health Sciences (NIEHS), part of the National Institutes of Health, the University of North Carolina (UNC) at Chapel Hill and the U.S. Environmental Protection Agency (EPA) analyzed data on young (18-35 years), healthy, non-smoking men and women to see if BMI - a measure of the amount of fat a person has calculated by the ratio of height to weight - had an effect on lung response to acute ozone exposure.
"It has been known for a long time that in response to short-term exposure to ozone lung function tends to temporarily drop in many people. There has recently been interest in why some people's lung function drops more than others. "Age and perhaps genetics, as well as diet may play a role," said London, an NIEHS researcher and co-author. "We were intrigued by recent mouse studies that showed that obesity increases lung responses to ozone and wanted to see whether this applied in humans."
To examine the question of whether higher body mass index influences ozone responses in humans, the investigators took advantage of an earlier study led by Milan J. Hazucha and colleagues at the Center for Environmental Medicine, Asthma and Lung Biology/UNC and the USEPA Human Studies Facility in Chapel Hill, N.C.
The study determined BMI in 197 subjects who had been exposed to ozone for 90 minutes, during which they alternated 20 minutes of exercise with 10 minutes of rest. The subjects' lung capacity and function were tested immediately before and after the exposure period using spirometry, a basic lung function test that measures the speed and volume of air breathed out of the lungs.
In general, the higher the BMI, the greater the ozone response, providing one more reason why maintaining a healthy body weight is important to good health. When subjects were put into categories of body fatness defined by the US Centers for Disease Control based on their BMI, the ozone-related drops in lung function, particularly the forced expiratory volume in one second (FEV1), were lowest in underweight people (BMI less than 18.5), greater in normal weight people (BMI 18.5 to 25) and greatest in overweight individuals (BMI above 25).
"It's notable that these results came out of a study that was done in a population of predominantly normal weight individuals," said London. "This suggests that these effects may be even more important in the general population where there are large proportions of overweight and obese individuals." An estimated two-thirds of U.S. adults are overweight or obese, with a BMI greater than 25, according to CDC (http://win.niddk.nih.gov/statistics/index.htm) .
The physiologic mechanisms responsible for the decline in lung function after ozone exposure with increasing BMI are not clear, although the authors suggest that perhaps circulatory hormones and other inflammatory factors may play a role. These factors have been shown to affect airway hyper-responsiveness and inflammation in animal models.
The authors note that the study was limited by the small number of obese individuals (the subjects had not been selected with a study of BMI in mind) and by having only one measure of a person's body fat. Future studies of the effects of obesity on ozone response, they say, should include a targeted pool of obese and lower weight subjects, as well as measures of central adiposity such as waist circumference, given that fat deposited centrally may have a greater influence on an individual's respiratory response to ozone.
The study was supported by U.S. EPA Cooperative Agreement CR824915 and CR829522 and in part by the Division of Intramural Research, NIEHS, NIH, HHS.
Reference: Bennett WD, Hazucha MJ, Folinsbee LJ, Bromberg PA, Kissling GE, London SJ. (http://www.ncbi.nlm.nih.gov/sites/entrez?Db=pubmed&Cmd=ShowDetailView&TermToSearch=17987466&ordinalpos=1&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSum) 2007. Acute Pulmonary Function Response to Ozone in Young Adults as a Function of Body Mass Index. Inhal Toxicol 19 (14): 1147-1154.
Hazucha, M. J., Folinsbee, L. J., and Bromberg, P. A. 2003 (http://www.ncbi.nlm.nih.gov/sites/entrez?Db=pubmed&Cmd=ShowDetailView&TermToSearch=12871968&ordinalpos=1&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSum) . Distribution and reproducibility of spirometric response by gender and age. J. Appl. Physiol. 95:1917-1925.