Breathing smoggy air diminishes the ability to breathe deeply in overweight people more than it does in lean folks. The new finding mirrors an effect recently seen in rodents.

About a decade ago, Milan J. Hazucha of the University of North Carolina (UNC) in Chapel Hill and his colleagues exposed people for 90 minutes to ozone, the primary respiratory irritant in smog. The goal had been to evaluate the effect of age on how sensitive adult lungs were to ozone levels representative of a very smoggy day.

But publication of the new animal findings prompted Hazucha's group to reevaluate data from that earlier trial. The researchers looked at healthy men and women for signs that ozone's ability to alter breathing capacity might have varied with body mass index (BMI), one measure of fatness.

"We didn't expect to see an effect," admits William D. Bennett of UNC, who headed the analysis. But a trend indeed emerged showing that, in general, the heavier a recruit had been, the more trouble he or she had breathing deeply after exposure to substantial ozone. The correlation proved significant only in women who, as a group, also exhibited a broader range of BMIs. Bennett's team reports its findings in the November 2007 Inhalation Toxicology.

The team is now recruiting lean and obese women for a follow-up trial to evaluate lung impacts during exposure to ozone, not just afterward. Unlike the earlier trial, this one will also probe for signs that ozone exaggerates a marker of asthma risk.

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