A recent study suggests that exposure to wood smoke can have different effects on the respiratory immune systems of men and women.
As part of the study, the scientists exposed men and women volunteers to wood smoke or filtered air prior to inoculating them with a standard dose of the live-attenuated influenza virus vaccine, which causes a natural, yet mild, immune response in the nasal passages.
They later discovered that the men exposed to wood smoke had significantly higher markers of an inflammatory response in cells that line the nasal. In contrast, for women, the wood smoke exposure appeared to lower markers of the inflammatory response.
When the researchers averaged out the data from men and women, as these sorts of exposure studies typically do, the analysis gave the false impression that the wood smoke had almost no effect on the immune response to the live-attenuated influenza virus vaccine. The study was published in the American Journal of Respiratory and Critical Care Medicine.
Ilona Jaspers, senior author of the study said, "The upshot is that we really need to consider sex-specific effects when studying wood smoke and other environmental pollutants that threaten public health."
Wood smoke is among the most ancient environmental pollutants and is still considered a significant cause of sickness and death today. Wood smoke contains dozens of known toxins, and epidemiological studies have linked biomass exposures to chronic obstructive pulmonary disorder in women who have never smoked and lung cancer in male firefighters. Wood smoke exposure is also expected to become more common as the frequency of wildfires increases.
Researchers estimate that about 40 percent of the modern human population, roughly 3 billion people, is chronically exposed to smoke from burning wood and related "biomass" combustibles, such as leaves, crop stalks, and dung.
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The scientists aren't yet sure why men and women would differ so starkly in their immunological responses to wood smoke. One possibility is that women and men over thousands of generations have had different evolutionary histories of wood smoke exposure, leading to different evolutionary adaptations.
Women, for example, might have had greater and more chronic exposure to smoke from cooking fires, compared to men. Other factors that may have influenced the sex-specific responses include differences in male and female hormone profiles and genetics.
"We wonder if a greater wood smoke exposure has led to evolutionary pressure on women to have a more blunted inflammatory response, which would probably result in less damage to the airway during respiratory virus infection," Jaspers said.
Regardless, this study suggests that any research on environmental exposures should take potential sex differences into account.