Petra Casey, M.D., is an Associate Professor of Obstetrics and Gynecology at Mayo Clinic. Her clinical and research interests include contraceptive technology and menopause management. She has co-authored over 50 peer reviewed publications and is leading a clinical trial focused on management of contraceptive implant-related bleeding.
Does a woman’s menstrual cycle affect her performance as an athlete? It's not always talked about publicly, but it's certainly discussed privately among female athletes. It’s also an issue that's just starting to be studied. Below is the transcript of an interview for the Office of Women's Health between Mayo Clinic gynecologist Dr. Petra Casey and Mayo Clinic News Network reporter, Vivien Williams.
VIVIEN WILLIAMS: An elite athlete or some women who exercise a lot, their periods may stop. What is that called? What causes it, and should we be worried?
DR. PETRA CASEY: So that is called hypothalamic amenorrhea, and what that means is that the hormones that are produced in the brain and then kind of cascade down to signal hormones that are produced in the ovary are not produced. So GnRH, the gonadotropic releasing hormone that is produced, triggers the follicular stimulating hormone, and the luteinizing hormone that are produced in the ovary, that signal does not translate to production of estrogen and progesterone, so the woman loses her periods. They may become irregular initially and then they may stop completely.
The trigger for that has been studied, and it’s still a little unclear whether it’s body fat percentage, whether it’s weight, whether it’s cortisol levels that stimulate decrease in GnRH, based on stress and the intensity of workouts. All of that is a little bit unclear, but, at the end of the day, a woman will not have her period if she is too lean, and she may be working out too intensely too long. Many women athletes are trying to actually become quite lean, because, in endurance sports, it’s advantageous to be lighter.
VIVIEN WILLIAMS: And will it come back? Is it dangerous?
DR. PETRA CASEY: Generally, it is reversible once she either decreases the intensity of her workouts, perhaps gains a bit of weight, and generally kind of gets more into what we would consider average weight or body mass index.
VIVIEN WILLIAMS: It’s interesting. It’s almost like an evolutionary thing. Your body is protecting itself because it could not support a baby.
DR. PETRA CASEY: Correct. It’s quite similar to when a girl would have her first period, because she needs to reach a certain threshold of weight or body fat percentage in order to start her periods. So this is kind of happening in reverse.
VIVIEN WILLIAMS: Is there anything dangerous about it at all?
DR. PETRA CASEY: Well, long term not having periods can be damaging because you are without estrogen, so bones tend to become thinner, so the development of osteopenia or osteoporosis, which may or may not reverse itself, because, as we are in our adolescent years and early 20s and then up to 30s, we are building peak bone mass. We reach peak bone mass around age 30.
So if most of those years have been spent in an amenorrhea state, no periods, because she is too lean. She’s working out very hard. Then she may never build that peak bone mass, and she will end up having osteoporosis later on in life. So that is – that is one worry.
Another worry is potentially cardiovascular risk, because, again, that estrogen is not there to protect the heart, so long-term effects on the heart. However, endurance athletes tend to have pretty healthy hearts.
VIVIEN WILLIAMS: Right.
DR. PETRA CASEY: It’s a balance. It is a balance.
VIVIEN WILLIAMS: It is a balance. And how typical is it for an endurance athlete to lose her period? Is it something that happens to everyone when they get to that physical state or not?
DR. PETRA CASEY: No, a lot of women don’t really. They can stand to be fairly lean and not – not lose their period. Some women just do it, lose their period at a not particularly lean body mass. It’s just a variable kind of that everyone has a little differently.
VIVIEN WILLIAMS: And it doesn’t affect ability to conceive after it comes back?
DR. PETRA CASEY: No. Once the periods are back and regular, she’s back to her baseline. So if she were able to conceive prior to that, she will again.
VIVIEN WILLIAMS: OK. And that’s kind of a good segue talking about the period and athletes. If you have a period and you’re an athlete, tell me about how that affects performance.
DR. PETRA CASEY: So that is a very complex issue, and a lot of people have studied it. And, again, there’s no consensus. Nobody knows. Nobody can agree. There are just as many studies that say that performance does not vary throughout the menstrual cycle as there are studies that say it does. In general, in those that say that there is a difference, they say that the sweet spot is somewhere between the middle of one’s period, believe it or not, which seems counterintuitive, to the end of the follicular phase, which is the first half of a woman’s menstrual cycle.
So if we look at the typical menstrual cycle that is 28 days long, we are looking at the first five days of bleeding on average. Then, the first 14 days are considered the follicular phase. That’s when the little egg is getting built up. And, then there is the second half, which, again, is about 14 days ─ is when the lining gets really lush and ready to accept a fertilized egg. So generally, the luteal phase is considered less favorable for athletic performance because of the extra estrogen that gets made in there.
So to compensate for that, studies suggest that women need to carb-load more during the second half of their menstrual cycle if they’re going to have an endurance event. However, there are just as many women athletes who set personal records during their luteal phase, during their menstrual cycle, during their follicular phase, whatever. So it’s very different in every woman.
VIVIEN WILLIAMS: Every woman has a different experience when she’s menstruating anyway, so what about controlling it with birth control pills to get into the sweet spot? Do people do that?
DR. PETRA CASEY: Great question. And there are ways to do that to sort of even everything out. However, then, remember you are adding progesterone. You are adding estrogen to the mix. So will that help? Would I do it right before a marathon? No. You’d want to try it out and see if that will actually help, because there has been just as much concern about women decreasing their performance level while on birth control pills. So the advice there is, if you’re going to do it, try it out before or use the lowest possible progesterone and estrogen level formulation that you can find.
VIVIEN WILLIAMS: Is there going to be like an issue about her manipulating her cycle?
DR. PETRA CASEY: No, because this is – this is not really performance-enhancing. It’s more, you know, she’s a woman. She needs birth control. And many, many women who are not athletes are using continuous birth control pills or are using continuous methods of birth control to not have periods even out of that arena. So I don’t believe so. But great question.
VIVIEN WILLIAMS: And it’s safe to mess with your cycle like that?
DR. PETRA CASEY: Oh, absolutely. Been doing it for decades.