Oral contraceptives may help lower the risk of sports injuries
Female athletes taking birth control pills were five times less likely to develop muscle or tendon injuries. But are the benefits worth the risks?
As the number of women participating in sports has increased in recent decades, there is now greater awareness that injuries female athletes experience can differ from their male counterparts. One reason, according to a growing body of evidence, is that hormones may play a role in increasing the susceptibility of female athletes to certain types of injuries.
Compared to male athletes, previous studies have found that female athletes are roughly two to six times more likely to tear the anterior cruciate ligament (ACL) in their knee, they are twice as likely to suffer concussions, and they are more likely to develop stress fractures. Other studies have revealed that a female athlete’s risk of injury varies depending on what phase of the menstrual cycle she is in, suggesting that changes in the levels of certain hormones can influencing athletes’ vulnerability.
We wanted to study how hormones influence muscles and tendons, says Yasin Dhaher, a researcher at UT Southwestern, whose research focuses on the off-target effects of oral contraceptives, and one of the authors of a recent study in Medicine & Science in Sports & Exercise. His team found that females taking oral contraceptive pills were about five times less likely to develop muscle or tendon injuries of the lower extremities, compared to females who were not taking these drugs.
These results underscore findings that hormone levels can impact a person’s susceptibility to injury, and that oral contraceptives can play a role in mitigating that risk.
“So many female athletes are on some form of birth control,” says Hope Welhaven, a scientist at Montana State University, whose research focuses on sex-based differences in injury prevention and recovery. She says that understanding the role that birth control plays in reducing sports injuries can offer insights into how to protect the health of all female athletes.
Differences in injury rates
Although the research is still in its early stages, what’s clear is that there is a difference in the rates and types of injuries sustained by male and female athletes.
“The injuries are often different,” says Candace Mason, an orthopedic surgeon at Baylor College of Medicine, adding that although female athletes are much more likely to tear their ACL, they are less likely to tear it due to contact injuries, and that they are more likely to tear the ACL of their supporting leg, rather than their leading leg. For the female athletes who do tear their ACL, they are about 25 percent less likely to return to their sport, compared to their male counterparts.
The reasons for these differences in sports injuries is still largely unknown; experts speculate that it is due to a complex mixture of anatomical, biological, and hormonal factors.
“We do know that there are anatomic, biomechanical, and hormonal differences, between men and women,” says Molly McDermott, a physician at the Cleveland Clinic, who specializes in sports medicine. Some of these include differences in total muscle mass, body fat percentage, and some biomechanical differences in bone and ligament structure, such as being “knock-kneed” or hypermobile, which can set women up for certain types of injuries.
Risk of injury changes depending on menstrual cycle
As several studies show, levels of hormones, such as estrogen, appear to play a role in injury rates for female athletes, with the risk for injury increasing at certain points in the menstrual cycle.
Although the evidence is still mixed, “most studies suggest women are more vulnerable to injury right around ovulation,” says Gillian Wooldridge, a sports medicine physician at Houston Methodist Hospital.
At this point in the menstrual cycle, estrogen levels start to peak, which is thought to contribute to injury risk by making the muscles and ligaments laxer, and therefore more prone to injury.
(The menstrual cycle can reshape your brain)
Although most of the studies have focused on the risk of ACL injuries, a 2021 study focusing on 113 female football players found the risk of muscle and tendon injuries did vary according to what stage of the menstrual cycle the athletes were in, with an increased risk for injury just prior to ovulation.
Oral contraceptive use linked to lower rate of muscle injuries
For Dhaher’s study investigating the link between oral contraceptive use and the risk of muscle and tendon injuries, researchers looked at a general population of patients between the ages of 18 and 39.
After matching patients for factors such as age and gender, they examined the prevalence of muscle and tendon injuries in female patients who were on oral contraceptives versus those who were not.
The analysis revealed that female patients not on oral contraceptives had an injury rate of 2.55 percent, compared to an injury rate of 0.55 percent in those who were taking oral contraceptives; a five-fold difference in muscle and tendon injuries.
“This is the first study that looks at muscle injuries and oral contraceptives,” Dhaher says. Although more research is needed, these lower injury rates are thought to be due to oral contraceptives having a strengthening effect on tendons and muscles, by reducing the fluctuations caused by changing levels of estrogen.
(Endometriosis is common, incredibly painful—and often misdiagnosed. Why?)
“It’s not so much the estrogen level itself, it’s the changing estrogen levels,” says Wooldbridge, adding that these shifting quantities of estrogen cause fluctuations in the strength and flexibility of muscles and tendons over the course of the menstrual cycle, which introduces an element of unpredictability that can make certain maneuvers possible at some points during the month, but not others.
“The body is having to constantly adjust,” says Wooldbridge, adding that although it’s not necessary to alter your workout routine based on the time of the month, it is important to listen to your body, and to adjust accordingly.
Oral contraceptive pills come with benefits and risks
Although the use of oral contraceptive pills has been linked to a lower risk of muscle-tendon injuries, it’s important to note that their use may not be for everyone, as there is a risk of side effects.
“If you want to start someone on birth control pills, you really want to know why,” says Gillian Wooldridge. People for whom taking oral contraceptives may be more risky include smokers over the age of 35, those with heart disease and or a family history of blood clots, and people who get migraines with aura.
For young female athletes, birth control pills are often used to restore their periods, which can stop due to a condition called relative energy deficiency syndromes, or RED-S—a pattern of declining athletic performance cause by a lack of calories. RED-S can increase risk of injury, including stress fractures, as well as boost the chance of irregular periods or stop them entirely. Over time, RED-S can decrease bone density, putting an athlete at risk for stress fractures and osteoporosis.
Although prescribing birth control pills for an athlete with RED-S can help restore their period, it won’t help resolve the energy deficit, nor will it help improve their bone density.
“There used to be this idea, just put them on a birth control pill, they’ll be fine,” says Michael Fredericson, an orthopedic surgeon at Stanford University. “At best, it might prevent further bone breakdown,” but it’s not going to fix the underlying issues, he says. Instead, as a study led by Fredericson showed, nutritional counseling was able to reduce the incidence of stress fractures in female runners.
In contrast, as a couple of studies have shown, young female athletes on birth control do show a reduced risk for injuries, but also an increased risk for reduced bone density, which may be due to being prescribed birth control pills to restore regular periods from undiagnosed RED-S.
“Ultimately, the correct answer is you want to figure out why they are not having regular periods,” Wooldbridge says.
As is the case with all medications, it’s important to know why you are taking oral contraceptives, what the potential side effects may be, as well as the potential benefits.
