Estrogen Protects Women from Flu

Influenza, more commonly known as the flu, is one of the common viral diseases. It manifests as fever, cough, sore throat, runny nose, headache and fatigue. A study was recently carried out that established the gender-specific protective role of estrogen against flu virus.

The study was led by Sabra Klein, PhD, of Johns Hopkins University and was subsequently published in the American Journal of Physiology -- Lung Cellular and Molecular Physiology.

The researchers found out that the hormone plays its defensive role mainly by affecting the virus’s ability to replicate. In order to determine exactly how the replication was influenced by the hormone, the researchers cultured nasal cells, the cells that are primarily infected by the Influenza virus. Influenza A virus strain was used in this study.

The nasal cells were collected from both male and female donors. The nasal cell cultures were then exposed to the virus, estrogen, the environmental estrogen bisphenol A and selective estrogen receptor modulators (SERM), compounds that mimic the action of estrogen.

Estrogen-The Guard Against Flu

 It was found that SERMs like raloxifene and bisphenol A decreased the replication of flu virus in nasal cells obtained from women but not men. The estrogens were observed to exert their effects via estrogen receptor beta. The female cells treated with estrogen or SERMs 72 to 24 hours before infection showed higher resistance to infection.

The findings confirmed that estrogen serves to defend the women from influenza virus. The study established that the protective role of estrogen in the general population is hard to investigate owing to the fact that the levels of estrogen undergo cyclical variation in women, especially in the pre-menopausal women.

Although the exact mechanism by which estrogens interfere with the virus’s replication is still unclear, according to the researchers, estrogen may interfere with viral cell metabolic rate which slows down the process of replication.

It was said that that women in their reproductive years, especially those on certain kinds of birth control and those receiving the hormone replacement therapy (HRT) are better protected from the virus during the seasonal flu epidemics.

The Future Implications

This study has brought the researchers one step closer to finding better treatment options for flu in the general population. Investigators are looking further into the role of SERMs and their potential to serve as the therapy for flu in women.

This study also widened the therapeutic benefits of estrogens which, besides being used for the treatment of infertility and menopausal symptoms, also serve as the medical therapy for influenza.  

According to the lead researcher Klein, previous studies have effectively established the antiviral role of estrogen against potent virus like HIV, Ebola virus and the Hepatitis viruses. This research has certainly brought the scientists another step closer to understanding the basic mechanism of the antiviral action of estrogen.

What makes this study stand out is the fact that it has probed into two main aspects of antiviral properties of estrogen. Not only has this study identified the gender-specific role of estrogen by obtaining direct cell cultures but has also identified the estrogen receptors that mediate these effects.  

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According to the lead researcher Klein, "Other studies have shown that estrogens have antiviral properties against HIV, Ebola and hepatitis viruses. What makes our study unique is two-fold. First, we conducted our study using primary cells directly isolated from patients, allowing us to directly identify the sex-specific effect of estrogens. Second, this is the first study to identify the estrogen receptor responsible for the antiviral effects of estrogens, bringing us closer to understanding the mechanisms mediating this conserved antiviral effect of estrogens."

Estrogen-Only Hormone Therapy Carries Lower Risk of Blood Clot Formation

Hormone replacement therapy (HRT) is used to treat a wide range of conditions in women. Recent evidence has come to light which suggests that estrogen-only hormone replacement therapy carries a significantly lower risk of venous thromboembolism (VTE) as compared to the combined estrogen-progesterone hormone therapy.

The study was carried out in over 800 Swedish women and was subsequently published online in Menopause, the journal of The North American Menopause Society. The 800 case subjects who had VTE were matched against 900 control subjects who took no hormones.

The basic aim of the study was to find out whether  lower doses or transdermal (through the skin) doses of estrogen-only or combined estrogen-progesterone hormone therapy carry lower risk of VTE or not.

Lower Risk of VTE with Estrogen-Only Therapy

The researchers came up with quite astonishing figures. The risk of developing VTE was almost 1.72 times higher in women taking hormone therapy as compared to those who took no hormones at all. The women taking combined HRT were found to have three times more risk of VTE when compared with women who were given no hormones.

Women who received estrogen-only HRT, mainly because they had undergone hysterectomy and did not need progesterone at all, were found to have the lowest risk of developing VTE- 1.31 times higher risk compared to the women who received no hormone therapy.

Women who received combined estrogen-progesterone therapy were discovered to carry a twofold higher risk of developing VTE when weighed against women receiving estrogen-only hormone therapy.

Route of Administration of Estrogens Makes A Difference 

The study came up with the astounding discovery about the route of administration of estrogens. It was found that there was no increased risk of VTE in women who used transdermal estrogen in the form of patches, either alone or in combination with progesterone.  

Women, who used vaginal estrogens to combat vaginal dryness and other symptoms of menopause, were also found to carry no added risk of VTE. This is thought to be due to the fact that the absorption of vaginally administered estrogens into the blood stream is relatively less which is why these estrogens result in the same effects as seen in women who received no hormones.

The Future Prospects

The question whether or not the dose and route of administration of hormone therapy in women makes a difference, has frequently gone unanswered. This study has helped resolve this issue and has helped direct the future studies towards finding hormone therapies that impart the maximum benefit with a significant reduction in their side effects, particularly VTE which proves to be fatal in most of the women.  

This study has also helped find the optimally beneficial route of administration which will benefit women in the long run by reducing the risk of blood clot formation.

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According to NAMS Executive Director JoAnn V. Pinkerton, MD, NCMP, this study has helped understand how transdermal estrogen therapy is safer than the oral one. It has also effectively established that various estrogen or progestogen combinations carry different risks.These findings will have a great impact in developing safe therapies via transdermal or vaginal route for women who are at high risk of blood clot formation.