How The Pill Might Help Fight The Flu

Are you currently on a hormonal birth control that includes progesterone? It may have an unexpected benefit: helping you get past the worst of the flu virus. No, really. A study just released from Johns Hopkins Bloomberg School of Public Health, conducted on female mice, found that progesterone is actually pretty helpful when it comes to the body's immune response and recovery from the flu, because of the way in which the hormone interacts with the immune system. We're still not entirely sure if this applies in humans, but if so, it's a wonderful addition to the whole no-babies thing.

Progesterone, in synthetic form as progestin, is used across a variety of birth control, from the combined pill (which adds it to estrogen) to the mini-pill (which is progesterin-only), implants, and hormonal IUDS. The interference of progesterone prevents ovulation and thickens the mucus in the cervix, creating a barrier to any entering sperm. But we're increasingly realizing that it's got more complicated impacts on female health than that. It seems to interact with our immune function and how we contract and recover from certain diseases, and the new study seems to uncover a possible function we hadn't previously known: when it comes to flu, a dose of progesterone might help mice kick its ass.

There are, however, a lot of reasons why this doesn't mean an end to all flu medication just yet. Let's get into the idea of mice with flu, what progesterone did to them, and why your birth control might have a deeply unexpected side effect.

How The Pill Might Ward Off The Flu

Here's how the study worked: the researchers took collections of female mice, all of whom had their ovaries removed so that they no longer had menstrual cycles or any natural levels of progesterone. They then gave some of them progesterone implants, rather like the ones we have in humans, to give them a constant level of progesterone circulating in the body, and left others without it. (The implants, it's important to note, were meant to mimic the doses we get in human progesterone contraceptives, scaled down for mice.) Then all the females were injected with influenza A, and carefully monitored.

The results were pretty surprising. The actual level of the virus, the "viral load," wasn't lessened in the mice with progesterone implants; but their physical reactions were. The female mice with implants were less likely to have hypothermia, recovered faster, survived longer, and also showed less inflammation and tissue damage in their lungs, which is where influenza A tends to hit hardest.

As with all good studies, this one raised even more questions than it did answers: What on earth was progesterone doing? Why were the results better for the implanted mice? The researchers found a few possible solutions. It turned out that the savior of the progesterone-heavy mice when recovering from serious flu was a protein called amphiregulin, which is produced by the cells that line the lungs. In further studies, the curious scientists found that a progesterone dosage seems to make amphiregulin levels spike; if they took away amphiregulin from the mice, the progesterone's positive impacts disappeared.

This is massive news: it basically indicates that, for a certain kind of tissue, progesterone is a fixer-upper. It "regulates the cellular and molecular mediators of tissue repair at a mucosal site outside of the reproductive tract to restore tissue homeostasis after infection or injury," in the words of the scientists. (In plainer English, it can do repair work outside of the uterus on various bits of the female body. Awesome.)

That wasn't all, either. Progesterone treatment in the mice also raised the levels of an immune cell called a T helper 17. (Look, naming things in medicine can get really complicated.) The reason this is good for flu sufferers? T helper 17 cells specifically target inflammation and mucous membranes, like those in the nose and the lungs. All in all, the progesterone dosage was a massive boost to the flu-ridden mice. But you can't start forgoing the flu vaccine and trusting your birth control to do all your work just yet.

Why You Shouldn't Get Too Excited Just Yet

This is usually the point where, discussing an exciting new discovery, I urge caution. And that's particularly the case this time. Mice are not humans, which may seem like a stupid observation; but considering some of the headlines about this discovery ("your birth control will stop you getting flu!"), it's pretty important to note. Just because female mice with progesterone implants get over the flu faster (or at least die at a slower rate), that doesn't mean you can start dosing up on progesterone supplements and convince yourself that you'll get through flu season more invulnerable than Luke Cage.

The NHS, which does regular reviews of attention-grabbing scientific discoveries, has a few interesting notes about why to take this study with caution. For one, they point out that there was no suggestion that having progesterone hanging around naturally might "protect" you from the flu; it just helped recovery. Even if the progesterone effects were the same in humans, you'd still be chancing it by hanging around flu-infected people while they sneezed. For another, the mice had their ovaries taken out, a profoundly abnormal state of affairs. The ones with a bit of replacement hormone, even if it wasn't completely usual, might have been able to fight off flu's effects better simply because they were closer to normal functioning.

Plus, science suggests that progesterone isn't a uniformly good idea for the human immune system. It seems that, while progesterone enhances our immune reactions in some areas, it's not great in others; a study in 2013 found that, in pregnant women or those using hormonal contraceptive injections, progesterone reactions left them more vulnerable to malaria, herpes simplex and HIV, among other diseases. So progesterone on its own isn't necessarily the answer. We're going to need a lot more science before we can give people progesterone-based treatment to get them over the flu, though it's worth not forgetting to take your birth control when you're suffering from it. Hey, safety first.

Images: Bustle; Giphy