Estrogen dramatically reduces the amount of flu virus that replicates in infected cells from women but not from men, according to a new study.
The study by researchers at the Johns Hopkins Bloomberg School of Public Health suggest a protective advantage to the quintessential female hormone that naturally circulates in women's bodies, as well as artificial forms given for hormone replacement therapy and estrogen-like chemicals found in the environment.
Recent studies have shown that estrogen can hamper replication of viruses including HIV, Ebola and hepatitis, which can lessen an infection's severity and make an infection less likely to spread to other people. But researchers said it was unknown whether estrogen might have the same effect on the flu virus.
To investigate, they collected cells from the nasal passage -- typically the first cells in the body to get infected with the flu -- from female and male volunteers.
Tests showed that female cells that received estrogens, including some types of SERMs and bisphenol A, had marked reductions of viral replications -- nearly 1,000-fold less compared to those that had not been exposed to these hormones.
Even though men produce estrogen, their cells have far fewer receptors for the hormone. That might be why estrogen did not have the same protective effects against flu virus replication in cells from men, according to the researchers.
"If women are taking estrogen-like hormones for other reasons, an added benefit might be less susceptibility to influenza during the flu season," said study leader Sabra L. Klein, an associate professor in the departments of molecular microbiology, immunology, biochemistry and molecular biology at the Bloomberg School.
The findings could be particularly important for elderly women, she added, since this population is most susceptible to severe influenza.
The findings were reported online last week in the American Journal of Physiology-Lung Cellular and Molecular Physiology.
