This is the first study in humans to look at whether body weight influenced how much lung function falls after acute ozone exposure. Ozone is formed in the atmosphere in the presence of sunlight from other 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 197 young (18-35 years), healthy, non-smoking men and women to see if body mass index (BMI)—a measure of the amount of fat a person has—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 NIEHS researcher and co-author Stephanie London, M.D.
She added: "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.
From this study, BMI was determined in 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 how fast and how much air is breathed out of the lungs.
The study says, the higher the BMI, the greater the ozone response. This in general provides one more reason of maintaining a healthy body weight for 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).
BMI is a measure of fatness based on an individual's height and weight. The study was done on normal weight individuals and proved that the effects will augment in the general population that consists of heavier people.
London added: "This suggests that these effects may be even more important in the general population where there are large proportions of overweight and obese individuals."
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.
The study was published this month in the journal Inhalation Toxicology.