Why women are more vulnerable to asthma risk than men

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Women are more likely to suffer from asthma than men because of the absence of testosterone -- the male sex hormone -- which prevents lungs from inhaling harmful pollen, dust or other airborne allergens, finds a study.

The findings showed that testosterone acts on immune cells that act as first line of defenders of the body against invading viruses.

These immune cells are linked to asthma symptoms, such as inflammation and mucus production in the lungs, which causes airways to narrow during an asthma attack.

"Initially we thought that ovarian hormones would increase inflammation, more so than testosterone making it better," said Dawn Newcomb, from the Vanderbilt University in Tennessee, the US.

"I was surprised to see that testosterone was more important in reducing inflammation," Newcomb said.

Prior studies have showed before puberty boys have approximately 1.5 times higher rate of asthma than girls. That trend reverses after puberty, when women are twice likely to have asthma as men.

This pattern continues until women hit menopause, and then the asthma rates in women start to decline, the researchers said.

For the study, appearing in the journal Cell Reports, the team focused on lung cells called Group 2 innate lymphoid cells, or ILC2 cells -- which make cytokines, proteins that cause inflammation and mucus production in the lungs, making it harder to breathe.

The researchers collected blood from people with and without asthma and found that those with asthma had more ILC2 cells than those without. Asthmatic women were found with more ILC2 cells than men.

In addition, when the researchers added testosterone, to the ILC2 cells, they found that the male hormone prevented the cells from expanding and reduced the production of cytokines.

However,"sex hormones are not the only mechanism but, rather, one of many mechanisms that could be regulating airway inflammation", Newcomb said.

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