Asthma More Common Among Women Because Men Have More Testosterone: Study

A new study has found a link between testosterone and asthma. The crippling lung condition, the researchers found, is triggered by a spike in a rare population of white blood cells in the body which testosterone helps control. This makes adult men less susceptible to asthma.

In children, asthma is more common in boys than girls. But around the time of puberty, there is a reversal. Adult and middle aged women were found to be twice as likely to be affected by bronchial asthma, compared to adult men.

The team of researchers from Vanderbilt University Medical Center in Nashville, Tennessee, found that the spike in the hormone called testosterone in men during and after puberty caused the rate of asthma cases to halve.

The researchers have figured out the science behind why testosterone inhibits the disease in men. A rare group of white blood cells called ILC2 have been known to trigger asthma in people. A spike in the number of ILC2 circulating in our blood increases our allergic responses which in-turn builds to asthma.

People with asthma have increased numbers of ILCs circulating in their bloodstream compared to their healthy counterparts.

The researchers used a method called flow cytometry to count the number of ILC2 cells in the blood stream in a test group which included adult men and women with moderate to severe chronic asthma and also a group of healthy adult men and women as study control.

The numbers revealed that in the healthy group, there was no significant difference in the ILC2 numbers between men and women. But, in the group with asthma, men showed a much lower ILC2 concentration.

The researchers further used mice to study the link between testosterone and asthma. The researchers found that the male sex hormone helped control the growth of ILC2 numbers in the body. Female mice had about 1.5 times as many of these immune cells as males.

Testosterone also helped control ILC2-mediated airway inflammation. This explains the increased number of asthma cases in adult women across the world.

According to the latest Centre of Disease Control and Prevention report released in 2015, the percentage of men and women who have ever had asthma was 11 and 14.3 percent respectively. In people still suffering from asthma, 9.7 percent of adult women still had the ailment compared to 5.4 percent of adult men.

When complications due to asthma are taken into consideration, the difference becomes more apparent. The National Health Interview Survey data showed that sinusitis affected 14.6 percent of the women suffering from asthma compared to 8.5 percent of the men. 2.6 percent of the men developed chronic bronchitis from the asthma compared to 4.6 percent of the women.

An estimated 358 million people had asthma in 2015. That year the disease was responsible for nearly 400,000 deaths, most of which occurred in developing countries, said a press release on the Vanderbilt University School of Medicine website.

The findings of the study could help improve the treatment of asthma worldwide. Further research could help develop targeted medication that will help fight the disease efficiently and control symptoms better.

"Defining the role of sex hormones on ILC2-mediated airway inflammation is imperative to effectively design future clinical trials and develop new therapeutic strategies for asthma and other ILC2-mediated diseases," the Vanderbilt researchers said in the report.

The study was published on Nov. 28 in the journal Cell Reports. It was led by Dawn C. Newcomb, assistant professor of Medicine and of Pathology, Microbiology and Immunology at the Vanderbilt University School of Medicine.