Breathing Smoggy Air More Dangerous for Fatter People

CHAPEL HILL, North Carolina (ENS) - The first evidence that fatter people with higher body mass index may have a greater reaction to smoggy air than leaner people was presented today by the National Institutes of Health.

Short-term exposure to ground-level ozone, or smog, is known to cause a temporary drop in lung function in many people, but this is the first study in humans to look at whether body weight influences how much lung function drops after acute ozone exposure.

Distinct from the strataspheric ozone layer high in the atmosphere that protects from the Sun's rays, ground-level ozone is formed in the atmosphere in the presence of sunlight from other pollutants emitted from vehicles, factories, power plants and other sources.

Researchers at the National Institute of Environmental Health Sciences, part of the National Institutes of Health, the University of North Carolina at Chapel Hill, and the U.S. Environmental Protection Agency analyzed data on young, healthy, non-smoking men and women 18–35 years of age.

They tested to see if body mass index, BMI, a measure of fatness based on an individual's height and weight, had an effect on lung response to acute ozone exposure.

The study published this month in the journal "Inhalation Toxicology" found that ozone response was greater with increasing body mass index, BMI is a .

"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, MD.

"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," she said.

As a start, the investigators took advantage of an earlier study led by Milan Hazucha and colleagues at the Center for Environmental Medicine, Asthma and Lung Biology at the University of North Carolina and the USEPA Human Studies Facility in Chapel Hill.

From this study, body mass index was determined 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 how fast and how much air is breathed out of the lungs.

In general, the higher the BMI, the greater the ozone response.

When subjects were put into categories of body fatness defined by the U.S. Centers for Disease Control based on their BMI, the drops in lung function, were lowest in underweight people, greater in normal weight people, and greatest in overweight individuals with BMI indexes greater than 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."

The Centers for Disease Control estimates that two-thirds of U.S. adults are overweight or obese, with a BMI greater than 25.

The physical mechanisms that causes the decline in lung function after ozone exposure with increasing BMI are not clear.

The authors suggest that perhaps circulatory hormones and other inflammatory factors may play a role because these factors have been shown to affect airway hyper-responsiveness and inflammation in animal models.

The authors note that the research was limited in the small number of obese individuals studied - 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.

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