Yes, Exercise Can Hurt Your Fertility. Here’s How to Exercise Safely.
There is a long history of sexist attempts to exclude women from athletic activities due to concerns about fertility. As recently as 2010, the ancient myth of the falling uterus was cited as a reason why ski jumping was “not appropriate for ladies.”
Needless to say, this idea is completely ridiculous. Women can run, jump, ski, bike, and swim without worrying about their vital organs falling into their spandex.
But women who are trying to conceive sometimes worry whether exercise could have an impact on fertility. We know those old myths about the falling uterus are sexist and false, but is there any truth to the idea that exercise could reduce your chances of conceiving?
It turns out, the answer is yes—exercise can have a profound negative impact on fertility if you’re not vigilant about eating enough. This post will explain how to exercise safely, and offer a few easy self-assessments you can do to get an idea whether your exercise routine is negatively impacting your cycle.
Wait, I Thought Exercise Was Healthy!
Let’s first get one thing out of the way: regular physical activity is beneficial for overall health and wellbeing. Exercise helps maintain healthy weight, improves cardiovascular health, and just plain feels good. There does not seem to be anything intrinsic to exercise that leads to reduced fertility[1.Loucks AB, Verdun M, Heath EM. Low energy availability, not stress of exercise, alters LH pulsatility in exercising women. J Appl Physiol. 1998;84(1):37–46.].
The problem arises for some women when there is an energy deficit—when you are burning more calories than you consume. But developing an energy deficit is much easier than many women realize.
Exercise & Energy Deficits
Your reproductive system is highly sensitive to energy deficit, and that’s a good thing. In times of famine, when our ancestors might have been walking many miles each day just to gather the bare minimum of calories, the ability to turn off the reproductive system probably helped our survival in the long run, allowing us to reproduce when we had enough resources to feed our children.
If you’re reading this post, you probably don’t worry about where your next meal is going to come from. So why should you even think about energy deficits? Well…are you a woman who maybe grew up steeped in messages about how your worth is in inverse proportion to your waist size? Have you ever tried to lose weight, cut out certain food groups, ignored your hunger signals, or increased your exercise without making a conscious effort to increase your calories? If you answered yes to any of these questions, chances are you have experienced energy deficit.
Keep in mind that you can experience energy deficit even if you don’t have a super low body fat percentage[2.Scheid JL, De Souza MJ, Hill BR, Leidy HJ, Williams NI. Decreased luteinizing hormone pulse frequency is associated with elevated 24-hour ghrelin after calorie restriction and exercise in premenopausal women. Am J Physiol Endocrinol Metab. 2013;304(1):E109–16.]. If your energy intake isn’t enough for your body to complete its basic functions, you are in energy deficit. If your BMI is 25 or lower, and you are trying to conceive, it may not be the best time to play around with energy deficit.*
If it’s surprising to hear that you can experience energy deficit even if you’re not underweight, you’re not alone. Most of us have a certain idea of what healthy looks like, and it involves a tight butt, nice delts, and certainly no cellulite or belly fat.
The thing is, just because someone looks healthy doesn’t mean they really are healthy. A healthy body is one that that allows you to have a healthy menstrual cycle. That may or may not look like the picture of health you have in mind for yourself.
How Big is This Problem?
Exercise related menstrual disturbances are common in women who exercise, with some studies estimating that up to 60 percent of exercising women experience some form of menstrual disturbance [3.De Souza MJ, Toombs RJ, Scheid JL, O’Donnell E, West SL, Williams NI. High prevalence of subtle and severe menstrual disturbances in exercising women: confirmation using daily hormone measures. Hum Reprod. 2010;25(2):491–503.].
One study that compared the cycles of exercising and non-exercising women found that among exercising women, 25 percent of cycles were anovulatory and 25 percent of cycles had short luteal phases. Only 48 percent of exercising women’s cycles were normal! (For comparison, 95 percent of non-exercising women’s cycles were normal.)
In another study that compared exercising and sedentary women, sedentary women were found to ovulate much more consistently than exercising women. Ninety-five percent of the sedentary women had consistently ovulatory cycles, compared to only 32 percent for the exercising women[4.Gibbs JC, Williams NI, De Souza MJ. Prevalence of individual and combined components of the female athlete triad. Med Sci Sports Exerc. 2013;45(5):985–96.].
If these numbers seems shockingly high to you, you’re not alone. It’s difficult to appreciate how widespread this problem is because the impact of energy deficit on fertility is not always obvious.
The most extreme form of exercise-related menstrual disturbance is hypothalamic amenorrhea, where the cycle stops completely. If that happened to you, you’d probably notice (unless you were on hormonal birth control, which masks the symptoms). But there are other, subtler menstrual disturbances that can occur even when a woman is getting a regular period. These “silent” menstrual disturbances are not easily diagnosed, but they can still contribute to infertility (not to mention other serious health consequences)[5.De Souza MJ, Toombs RJ, Scheid JL, O’Donnell E, West SL, Williams NI. High prevalence of subtle and severe menstrual disturbances in exercising women: confirmation using daily hormone measures. Hum Reprod. 2010;25(2):491–503.].
Most women have no idea what’s going on in their cycles beyond when they get their period. And it’s not as easy as it seems for a doctor to uncover these problems, because it would require testing hormone levels at many different points throughout the cycle. The most important thing you can do to ensure your cycles are healthy is to learn how to track them.
Here’s the spectrum, in order of severity:
Luteal Phase Dysfunction
A normal luteal phase is 12 – 14 days. But with energy deficit, you may have a regular, ovulatory menstrual cycle, but your luteal phase is 10 days or less. Short luteal phases are often accompanied by prolonged follicular phases; you could have a textbook 28-day cycle, with a 21-day follicular phase and 7-day luteal phase. With luteal phase defects, chances of conceiving are diminished.
In an anovulatory cycle, estrogen doesn’t rise high enough to initiate the feedback loop that causes ovulation to occur. It’s possible to get your period regularly without ovulating (you can confirm whether your cycle is ovulatory by taking your temperature).
Energy deficit can lead to long, irregular cycles that may be ovulatory or anovulatory. This condition is not well understood, and comes with highly erratic hormonal profiles. One of the most common causes of irregular cycles is PCOS, but energy deficit can also cause irregular cycles. Distinguishing whether irregular cycles are caused by energy deficit or PCOS is tricky and requires careful screening, but it’s important, because the treatment for PCOS and energy deficiency are not the same.
The most severe form of menstrual disturbance is the total cessation of the menstrual cycle. It’s impossible to get pregnant when you don’t have a cycle, and it comes with a variety of serious health consequences unrelated to fertility.
The Good News
If this post depresses you, don’t worry, there’s plenty of good news, too:
Exercise is not the problem!
Studies have looked at whether there is something intrinsically problematic about exercise itself, and the research seems to suggest that there is not. It’s really just about energy deficit. But given the high prevalence of menstrual dysfunction among ovulatory women, it seems that developing an energy deficit is much easier than many women realize. The good news here is that if you are vigilant about taking in enough calories to account for your activity levels, you should be able to maintain a healthy cycle.
Exercise does not appear to cause permanent damage to fertility.
When you fix the energy deficit, fertility should return completely intact[6.Bullen BA, Skrinar GS, Beitins IZ, von Mering G, Turnbull BA, McArthur JW. Induction of menstrual disorders by strenuous exercise in untrained women. N Engl J Med. 1985;312(21):1349–53.]. The process of recovery may take some time, and usually involves moving backwards along the spectrum mentioned above (from hypothalamic amenorrhea to irregular cycles to anovulation to short luteal phase and finally back to healthy cycles)[7.Mallinson RJ, Williams NI, Olmsted MP, Scheid JL, Riddle ES, De Souza MJ. A case report of recovery of menstrual function following a nutritional intervention in two exercising women with amenorrhea of varying duration. J Int Soc Sports Nutr. 2013;10:34.]. That’s why it’s important to make sure that energy balance is restored completely, so you don’t end up in one of the subclinical recovery stages. (Restoring energy balance can take some time, and when you’re trying to conceive, you’re probably not at your most patient. Fertility medications can definitely help speed things up, but these are not usually effective unless you have already made a big dent in the energy deficiency on your own via reduced exercise and increased calories.)
If you need to gain weight, it may not be much!
The amount of weight that needs to be gained to regain healthy cycles is usually not exorbitant [8.Mallinson RJ, Williams NI, Olmsted MP, Scheid JL, Riddle ES, De Souza MJ. A case report of recovery of menstrual function following a nutritional intervention in two exercising women with amenorrhea of varying duration. J Int Soc Sports Nutr. 2013;10:34.]. Five or ten pounds may be all that stands between you and optimal health and fertility. Is fitting into size 0 jeans important enough to sacrifice those things?
- Energy deficit can really mess up your cycle
- It’s much easier to develop an energy deficit than many women realize—especially if you exercise
- Your idea of what “healthy” looks like—flat abs, toned butt, no love handles—might not actually be healthy for you. For many women, the amount of calories required to avoid an energy deficit simply is not compatible with that kind of body. The body that allows you to have a normal menstrual cycle is the one that’s healthiest.
*This post does not cover energy deficiency for women with BMI above 25. While it is still possible to develop menstrual disturbances from rapid increases in intense exercise and decreases in calories, there are also fertility benefits associated with gradual weight loss when one is overweight. This is a complex subject that we will tackle in another post!