Researchers from Johns Hopkins Bloomberg School of Public Health in Maryland recently made a surprise discovery during a mouse trial: progesterone appears to reduce the symptoms of influenza infection and help lungs heal at a faster rate.

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Results from a recent experiment show that progesterone may help fix lung damage.

Progesterone is a naturally occurring steroid; it is heavily involved in the menstrual cycle, pregnancy, and the growth of the fetus.

A progesterone analog is the main constituent of the female contraceptive pill and, as such, is taken regularly by an estimated 100 million young adult women throughout the world.

A seemingly unrelated but similarly common occurrence is influenza. In America, millions of individuals each year are affected by flu, hundreds of thousands are hospitalized, and tens of thousands die.

Women of reproductive age are twice as likely as men to experience complications related to influenza infection.

Perhaps surprisingly, despite the high numbers of women taking progesterone-based drugs, little is known about how the hormone interacts with infections, other than sexually transmitted diseases.

Sabra L. Klein, Ph.D., associate professor of molecular microbiology and immunology, set out to investigate the role of progesterone on the symptoms of an influenza virus infection. The results are published this week in PLOS Pathogens.

The team of researchers placed progesterone implants in some female mice and left others without; they then infected all the mice with the influenza A virus.

Both groups of mice became ill, but the mice implanted with progesterone showed better lung function, less pulmonary inflammation, and any damage to the lungs was repaired more swiftly.

The increased speed of repair was a surprise to the researchers. Medical News Today recently asked Klein about the results and how they matched her expectations.

We initially thought that progesterone may make flu worse in females because pregnancy is a known risk factor. Instead, we observed that progesterone significantly protected female mice against severe disease by mitigating inflammation and improving pulmonary function.”

Sabra L. Klein, Ph.D.

Of course, a surprise result merits further inspection, so Klein and her team set about investigating the origins of progesterone’s unexpected interaction.

It seems that progesterone enhanced lung protection by increasing the production of a growth factor – amphiregulin – in the lining of the lungs.

Klein told MNT that the “observation got us thinking about how the lungs repair themselves after an infection, which brought us to growth factors, like amphiregulin. When we measured amphiregulin, sure enough, it was unregulated in females treated with progesterone.”

Hormones are known to affect a wide array of tissues, but, as Klein explained to MNT, this “was the first time that the hormonal influences on an epithelial growth factor have been observed outside of the reproductive tract.”

To double check the results, the team bred mice that did not produce amphiregulin. As predicted, once infected by influenza, the mice no longer benefited from the protective powers of progesterone.

When females get sick with the influenza virus, progesterone naturally falls. Any females who are using progesterone-based contraceptives override this reduction and receive a steady stream of progesterone.

To date, there is no scientific literature providing information about the potential relationship between the severity of flu and progesterone. To this end, researchers at the Johns Hopkins Center of Excellence for Influenza Research and Surveillance, who take questionnaire data about influenza, have started routinely asking about birth control.

Eventually, responses to these questionnaires will plug the knowledge gap, giving scientists a better idea of how this protective effect might work in humans.

When MNT asked about any future studies, Klein responded:

“We are now conducting studies showing that synthetic forms of progesterone, including levonorgestrel, found in hormone contraceptives and hormone replacement therapies also protect against flu, which has farther reaching implications.”

This finding opens an entirely new avenue of research; and, because progesterone-based medication and influenza are widespread across the planet, any discoveries are likely to be far-reaching.

Learn about current research into a birth control pill for men.