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There’s Finally Research Into Menstrual Cycle Changes Caused By COVID-19 Vaccines

Plus, what else you should know about the immune system’s role in your menstrual cycle.

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More and more athletes are leaning into menstruation-tracking technology to inform their training (even if the science hasn’t quite caught up with it). For some, it’s proven to be a useful tool in pinpointing when they might experience their best performances and, on the flip side, when to expect dips in energy.

There are many reasons why runners who menstruate should be familiar with their cycle. For one, if your period is particularly heavy or painful, it could be helpful to plan for those off or easy days in training. Heavy bleeding can also lead to iron deficiency, which will also have an affect on performance.

Ashley Plummer, D.N.P., a women’s health nurse practitioner at the University of Colorado, believes women would train differently if better equipped with information. “A lot of [athletes] have started tracking their cycles and training around their cycles, just based on a small amount of research we do have,” she says. 

It’s also important to pay attention and know what is normal for you and what might require attention from a professional.  We’ve heard time and again that we have to be our own advocates when it comes to getting the right medical care. That was  highlighted when COVID vaccines were authorized for emergency use.

When vaccination became widely available, reports of inexplicable changes to people’s periods lit up individual text threads, Twitter, and Reddit forums. Menstruating people widely shared their experiences trying to understand if they were alone in their experiences. It seemed obvious—and ignored—that a COVID vaccine affected menstrual cycles. 

What We Know About COVID Vaccines and Menstrual Cycle Changes

As a whole, research on menstruation and athletic performance is thin, as are other important aspects of women’s health. 

“Women haven’t always been prioritized in research, so we’re still really learning about women even though we’re half the population,” says Brandi Ring, associate medical director and OB-GYN at The Center for Children and Women in Texas. 

Changes to menstruation were not listed as a side effect of the vaccines. Dr. Victoria Male, a lecturer in reproductive immunology at Imperial College London, wrote in a journal article arguing that the phenomenon warranted studying. According to her, 30,000 reports of menstrual changes had been made to a UK government site for reporting drug side effects. 

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The grants and research followed. 

In August, the NIH awarded grants totaling $1.67 million to five institutions (Boston University, Harvard Medical School, Johns Hopkins University, Michigan State University, and Oregon Health and Science University) to study potential links between COVID-19 vaccination and menstrual changes including flow, cycle length, pain, and other symptoms. 

While the COVID-19 vaccines have been proven to be safe and effective, it’s still important that women know what is expected and when to seek medical attention.  

There are several possible causes for the changes people are seeing in their menstrual cycle including lifestyle changes related to the pandemic, pandemic-related stress, or actually having a COVID-19 infection since we know infections can throw off the cycle in some cases. 

Dr. Ring suspects pandemic and vaccine-related stress is a big factor. “I think what people underplay is the effect of stress and the stress hormone cortisol,” she says, noting that stress levels have been unprecedented for nearly two years. “We know that women are disproportionately affected by the stresses of the pandemic,” she adds. 

Anytime your body is stressed, there is a chance that your cycle could be thrown off. “Whether that is a big test coming up, a big presentation at work, or a big race, we can see menstrual cycle changes just from stress. We can also see it in women who are overtraining” she says. 

One of the first studies to come out of the NIH grants was led by Dr. Alison Edelman from Oregon Health and Science University, who notes that the research was prompted by the public’s interest and concern for menstrual health. Collecting data from a sample of around 2,400 vaccinated and 1,500 unvaccinated people, the team found that on average individuals experienced a .71-day cycle increase after the first dose and .91-day increase after the second dose. 

“Our team was very open to what we might find. We know that menstrual cycles have a normal variation to them already, plus we know that the immune and reproductive systems ‘talk’ to one another. A vaccine’s job is to produce an immune response, and we know that an acute immune reaction can cause temporary menstrual cycle changes,” says Dr. Edelman. 

The vaccine is a stressor in itself, says Plummer, on top of the psychological stress of the pandemic. ​​”MRNA vaccine, it actually does create a robust immune response or to put it simply, it creates a stressor on the body, as do almost all vaccinations.” 

According to the International Federation of Gynecology and Obstetrics, variation in cycle length by up to a week is classified as normal. 

“These results provide, for the first time, an opportunity to counsel women about what to expect from COVID-19 vaccination so they can plan accordingly,” said Dr. Diana Bianchi, director of NIH’s National Institute of Child Health and Human Development, in a press release earlier in the month. 

Additionally, the findings are reassuring for women who were wary about the effects the vaccine would have on their cycle. “If menstrual disruption is the only reason an individual is not considering COVID-19 vaccination, this research should be reassuring that potential changes are minimal, appear to be temporary, and, in alignment with other research specific to fertility and pregnancy, do not appear to cause long-term health or reproductive impacts,” says Dr. Edelman. 

That particular research, however, did not look at other characteristics of menstruation including variation in symptoms or changes in flow—which have been self-reported. 

Dr. Ring advises that if your menstrual cycle becomes irregular, first take a pregnancy test, and if it doesn’t return to normal within three to four cycles, you should check in with your physician. And Plummer also notes that if you are postmenopausal and have bleeding, you should get checked out. 

While women are choosing to be more dialed into their cycles for a multitude of reasons such as family planning, optimizing training, or just due to access to more technology, it’s also worth it to know how your immune system can throw a wrench in it all. After all, our immune systems have really stolen the show during the pandemic.

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Does Having a Menstrual Cycle Change the Way We Experience Illness?

According to the Cleveland Clinic the immune system really goes to work pre-ovulation to prepare for a problem-free fertilization and implantation. It then dials back afterward.  

“There’s a lot of research into how the types of immune cells that we have respond to the different hormones of the menstrual cycle, in particular progesterone and estrogen,” says Dr. Ring. “And there are periods during the cycle, when it does seem like maybe women are more susceptible to getting illnesses or are more or less likely to fight off viruses and bacteria.” 

During the luteal phase in particular, Plummer notes, it’s not uncommon for women with autoimmune disorders to have flare ups in their symptoms, as an example. But it’s not so cut and dry. Dr. Ring points out that the immune system is very complex with many types of immune cells at play. 

It’s reasonable to think differently about your behaviors in regard to this dip immunity while COVID cases surge, says Dr. Ring. For example, you may choose to stay in or be more diligent about wearing a mask during that time. It might also be a time that you prioritize things we know bolster the immune system, like getting enough sleep, eating a balanced diet, and maintaining physical activity.

For runners, it could be helpful to plan your training around the rises and falls in your immune system—hitting a germy indoor gym when it’s high and opting to run outdoors when it’s low. 

But does that change in immune robustness affect your performance? Probably not, says Dr. Ring, who notes that women have “won their races and broken world records in all phases of their menstrual cycle.” 

It’s also not unusual for an illness to affect the menstrual cycle temporarily. “The body preserves the ability to fight off that infection,” says Dr. Ring.

Still have questions about your period, your training, and anything else related to women’s health? Keep asking—maybe someday we’ll get the answers. 

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