Researchers at the Johns Hopkins School of Public Health are finding that the sex hormone progesterone has effects far beyond the reproductive system. Among the newly discovered properties of the female sex hormone, two stand out in particular: the ability to suppress some of the worst symptoms of seasonal flu infections and the accelerated healing of damaged lung cells. Dr. S. Klein, head of the study, says that according to the World Health Organization, more than 100 million women of reproductive age use progesterone contraceptives, without knowing how they affect the immune defense against infectious diseases, other than sexually transmitted. The goal of the scientists was to find new harmful side effects of taking progesterone, but instead – they found two positive side effects. In the course of the study, two target groups were observed: 1st, taking progesterone and 2nd – not. They were deliberately infected with the influenza A virus and strictly monitored. A serious difference in the course of the disease was found in the two groups. In the first one, significantly better respiratory function and less severe lung inflammation were reported. This impressed the scientists, but they were completely unprepared when they found that the lung cells of the first group of volunteers recovered from the infection significantly faster than those of the second group, which did not receive progesterone. NEWS_MORE_BOX Scientists have found that the protective effect of progesterone against influenza infection is indirect and is due to the increased production of the lung protein amphiregulin. It is not yet clear by what mechanism the sex hormone stimulates the additional release of amphiregulin, but the scientists were able to prove the observed effect in their publication in the journal PLOS Pathogens, 2016. Amphiregulin is a member of the family of epidermal growth factors and acting on certain tissue receptors in white lungs stimulates the growth and development of certain lung cells. Through this, a faster recovery of the lung tissue is achieved after the flu infection, the scientists are convinced. They hope their research will shed light on as yet unknown side effects of taking progesterone birth control. In this case, the side effect is highly positive, but even its exact mechanism has not yet been established, and since growth factors are indirectly affected in organs separated from the reproductive system, scientists are rightly concerned about the still unknown negative side effects.