Women have an immunity advantage over men, and the latest science says that estrogen levels are partly to thank. Find out what that means in the pandemic and beyond.

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Among the revelations that have come from crunching the pandemic stats is that men have been hit harder by COVID-19 than women.

Why? A new study in the journal Physiological Reports found one aspect that affords women added protection: estrogen. Both women and men produce this sex hormone — as well as the sex hormone testosterone — but women have more of the former, while men have more of the latter. When researchers treated cells with estrogen before and after infection, they found that the estrogen reduced the viral load of COVID-19 in the cells. They proposed that doctors could possibly use estrogen as a "potential therapeutic promoting cell protection" against the virus. (BTW, double masking can also help protect you from the virus.)

The Surprising Role Sex Hormones Play In Immunity
Credit: Alex Sandoval

Sex Hormones' Effect On Immunity

To unpack why estrogen was so potent in the COVID-19 study, it helps to know these hormones have an effect on the body by sending signals through receptors. "Immune cells are rich with estrogen receptors," says Sabra L. Klein, Ph.D., a professor of molecular microbiology and immunology at the Johns Hopkins Bloomberg School of Public Health. These estrogen signals switch on the immune cells, causing inflammation as they fight off pathogens.

Testosterone, meanwhile, has the opposite effect, suppressing inflammation. "Testosterone is generally anti-inflammatory and reduces many of the immune responses that are needed to fight an infection," says Klein. This dampening effect contributes to reduced immunity — and inflammation — in men. (Luckily, exercise can help boost your immune system.)

The Link with Your Monthly Cycle

Estrogen levels vary over the month — they are higher right before ovulation and drop right after. This has scientists pondering whether it's preferable to get a vaccine when estrogen is at its peak. A recent study by Klein and her colleagues at Johns Hopkins showed there was an association between estrogen and greater immunity from the flu vaccine in humans and mice, meaning the booster resulted in women producing more antibodies as protection.

Despite this variability during a cycle, women seem to enjoy a better blanket-immunity protection, including those who are on oral contraceptives or hormone replacement therapies. "What I've always found remarkable is that women have greater immunity than men without accounting for their cycles," says Klein. (Related: What Is Estrogen Dominance — and How Can You Rebalance Your Hormones?)

Regardless of estrogen's potential pathogen-fighting abilities, your best source of protection against COVID-19 is the vaccine. Both the Pfizer and Moderna vaccines are more than 90 percent effective in protecting the body from infection (and no, neither will cause infertility). So if you're able to, sign up to get your shot, and of course, post your #vaxxie afterward.

Shape Magazine, April 2021 issue