According to a 2009 survey from The Journal of Obstetrics and Gynaecology Canada, more than 40 per cent of women were using oral contraceptives at the time, and less than four per cent were using newer forms of birth control (like IUDs). While birth control in its various forms is very common, we still know little about how contraceptives can affect athletic performance. We spoke with exercise physiology PhD candidate Alexandra Coates, who helped us wade through the science to bring women runners the best possible information.
The first thing Coates wants runners to know is this is a very new field of research, and a lot of study results conflict with each other. She adds that there are also many different types of hormonal contraceptives, with different concentrations, types and cycles of synthetic hormones, which makes the research difficult to perform and interpret.
Coates points to a systemic review and meta-analysis published in July 2020, which found that athletes taking oral contraceptives may experience a very small reduction in exercise performance. The authors acknowledged that this difference was minor, and noted that on an individual basis, the effects will depend on the athlete’s reason for taking contraceptives. For example, if an athlete suffers from extremely painful periods, or has other negative symptoms throughout their menstrual cycle, taking a hormonal contraceptive that reduces these issues is more likely to help their performance.
Is one type of birth control better than the other?
Coates explains there are many different types of birth control, and each has pros and cons. She says this is because exogenous (supplementary) hormones will first suppress your own natural production of hormones, and then will act in your body in similar, but not identical, ways to regular hormones. This means that all types of hormonal birth control will come with side effects and possibly detrimental health outcomes.
“Broadly, I think it is important to understand the reason why you are on contraception,” she says. “The least amount of synthetic hormones you can expose your body to and still have the desired outcomes appears to be your best bet for health and performance.”
Below, Coates breaks down the positives and negatives of different types of birth control.
Hormonal oral birth control
In general, with hormonal birth control you are suppressing your natural ovulation and normal period (bleeding on the pill is called “withdrawal bleeding,” and isn’t a real period), which means you should have fewer of the negative symptoms around your period, you will lose less blood (good for prevention of anemia) and you won’t get pregnant. You can also control your new synthetic cycle compared to your natural cycle, so for example, if you have a race coming up and you don’t wish to go through withdrawal bleeding during competition, you can skip the bleeding altogether.
One major drawback to hormonal birth control is that it’s more difficult to assess your RED-S (relative energy deficiency in sport) status because your bleeding isn’t a real period. It also typically elevates your core temperature, which can increase muscle fatigue and impair your performance in the heat (or expose you to a higher risk of heat-stress injury). Additionally, there is a blood clot risk associated with the estrogen-progesterone pill, and it can also cause water retention, some weight gain and possibly disrupt your electrolyte balance, which can make it even more difficult to regulate your body temperature.
The levonorgestrel IUD provides only a small amount of synthetic progesterone that is relatively localized, and so you are exposed to less circulating exogenous hormones. For this reason, Coates says it may be your best option if you wish to go on hormonal birth control in order to lessen your period and period symptoms. It may either suppress or lighten your mood, so some athletes may benefit from a mild mood boost, but for others it may have the opposite effect.
The main drawback of an IUD is it is painful to insert and have removed, and Coates suggests athletes will want to take a couple of days off from training after having one inserted. An IUD will also make it more difficult to assess RED-S status, and you are still exposing yourself to some synthetic hormones, which will always put you at risk for some health-related side effects.
A note on copper IUDs: Coates says that since these don’t use synthetic hormones, the copper IUD is a great option if your main reason for birth control is to prevent pregnancy, but if you suffer from painful or heavy periods, it may make this worse.
The bottom line
“My advice to athletes is to really consider why they are going on birth control before picking a method, and then to try to pick the method that fulfills their needs without exposing them to too many negative side-effects,” says Coates. “I’d also say that athletes should really dig in and do some research to figure out the best option for themselves.”
Ultimately, she says that if you can go without hormonal birth control, that is likely your best bet for performance, but that’s with the caveat that every athlete has different reasons for going on birth control, and that prevention of pregnancy is as good a reason as any.