Menstrual Cycle Dysfunction in Female Athletes

The menstrual cycle is a highly regulated physiological process that occurs in the female body making conception and pregnancy possible. A number of hormones are involved in the regulation of this process, however, the smallest of changes in these hormone levels is, in some cases, enough to result in menstrual cycle disturbances. 

If you are not familiar with the female menstrual cycle and the key hormones involved or would like a refresher, follow this link and check out JPS’ very own Martin Refalo’s Crash Course on the physiology of the menstrual cycle. This will help get you up to speed.

Menstrual dysfunction among females, unfortunately, is common, particularly in endurance and aesthetic sports, however, recreational athletes are also at risk (1). The causes are varied, however hormonal status, training and physical parameters, nutrition and psychological stress are all potential factors. The prevalence of menstrual cycle dysfunction will often vary heavily depending on the type of exercise or sport. However, in studies of a mix of both recreational and competitive athletes, it has been identified that menstrual cycle abnormalities including luteal defects (27%), anovulation (25%), oligomenorrhea (3.5%), and amenorrhea (34%) are prevalent among exercising women (1). Studies suggest that approximately half of all exercising women experience abnormal menstrual cycles, which presents a dangerous situation (2). Presence of such disturbances places these individuals at a higher risk of developing osteopenia and bone-related injuries compared to normal menstruating athletes or non-athletic normal cycling females (3). These individuals are also at an increased risk of developing disordered eating behaviours, which over time, could potentially progress to a diagnosable eating disorder, such as anorexia or bulimia (4). Given such a strong and well-established connection exists between menstrual dysfunction, athletic training and disordered eating, greater attention and consideration among female athletes and coaches is necessary. This is not only to increase awareness but also implement preventative measures to avoid negatively impacting the health and performance of the individual.

Causes of menstrual cycle dysfunction

As mentioned there are a number of variables thought to be associated with menstrual dysfunction in female athletes. Due to the lack of specific criteria for defining menstrual categories, subjective data collected from athletes has been primarily used to evaluate the variables thought to be associated with the incidence of amenorrhea, one of the most common menstrual disturbances and one that will we will primarily focus on in this article.

Before we get started a couple of definitions to ensure we are all on the same page. 

Amenorrhea

• Primary amenorrhea – Failure to initiate menses by the age of 14 years in the absence of secondary sexual characteristics or the absence of menarche by age 16 regardless of the presence of normal growth and development of secondary sexual characteristics (5). 
• Secondary amenorrhea – Cessation of a regular menses for three months or more or the cessation of irregular menses for 6 months or more (6). 

Eumenorrhea

• Healthy, normal menstrual period. A high degree of inter and intra-individual variability exists; however, a “normal” cycle generally occurs every 21-45 days.

1. Body composition

Probably one the most common reasons often thought to be the cause of both primary and secondary amenorrhea is an individual’s body composition, and more specifically their body weight or body fat percentage. 

It is commonly thought the presence of menstrual irregularities only occur in females of lower body weights. However, several studies have found amenorrhea and eumenorrhea can exist in athletes of similar body weights, and in some cases, the amenorrhoeic athletes were actually heavier (7). Although this relationship is not well understood, it does appear that athletes of lower body weight (among other factors) could potentially be at a greater risk of menstrual irregularities. 

Low body fat percentage is frequently raised as a significant contributing factor to the menstrual irregularities that exist among many female athletes. Nearly 30 years ago, a theory stating that 17% body fat was necessary for females to initiate and maintain a normal menstrual cycle was proposed, however, although it seemed logical, further research rendered the theory invalid with evidence of normal menstruation in females of less than 17% body fat (7). Studies have also presented female athletes of identical body fat levels where one group still had their menstrual cycle while others had developed amenorrhea. Quite simply, body fat levels may be a contributing factor to menstrual irregularities, however, they are not the only factor. At best it could be proposed that amenorrhoeic females have slightly lower average body fat levels and are therefore at a higher risk of menstrual irregularities than females carrying more fat (8).

2. Training Load & Intensity

Training load and intensity in isolation do not appear to be strongly correlated with the development of menstrual abnormalities, however, in the context of decreased body weight or periods of increased stress (such as a dieting phase) training parameters could potentially play a more significant role (8). Consistent with research into other factors contributing to menstrual abnormalities, results have been conflicting. This is likely due to both intra- and interindividual differences of the menstrual cycle. However several associations have been consistently demonstrated. Studies have shown that when training load increases dramatically and the individual has no time to adapt, the risk of menstrual abnormalities increases. When combined with weight loss or dieting, this risk is further increased (8). Quite simply, performing a large amount of intense exercise without gradually building towards this load may result in menstrual issues. Add to this the stress of weight loss or dieting and the problem worsens. Further to this, the more weight loss and the younger the women, the more likely menstrual disturbances will occur. 

A potential explanation for this association may be the individual’s cortisol levels. Cortisol is a steroid hormone (typically known as the stress hormone) and is made in the adrenal glands and released in times of stress. The resulting effects see an increase in

heart rate, blood pressure, blood glucose, respiration and muscle tension. Due to its connection to the stress response, cortisol is often referred to as the “stress hormone.” Research on athletes has shown cortisol levels in amenorrhoeic athletes are 25% higher compared to sedentary and normal cycling athletes (8). Training is considered a stress on the body, hence the release of stress-related hormones. This stimulates the release of cortisol from the adrenal glands, which has been suggested to have a direct effect on the reproductive system and ultimately the female menstrual cycle. 

3. Nutritional Inadequacy

Insufficient caloric intake, with or without physical training, has the potential to contribute to menstrual abnormalities in some individuals. Amenorrhoeic athletes tend to consume fewer calories and grams of fat per day compared to their eumenorrheic counterparts (7). This is not true of all amenorrhoeic athletes as some studies have concluded that total energy intake has no influence on menstrual function, however, a potential relationship may exist (7). 

Further to this, the reduction in resting metabolic rate (RMR) that often accompanies calorie restriction, likely due to losses of lean body mass, is potentially another factor contributing to menstrual irregularities (8, 9). Not all females experience the same metabolic changes in a calorie-restricted state therefore generalizations cannot be made. That being said, calorie deficits may work in a synergistic fashion with training intensity to alter menstrual function (8). Although, evidence has yet to confirm whether the relationship between insufficient energy intake and exercise-induced menstrual irregularities is causal, therefore at this stage remains only a correlation.

Macronutrient composition of the diet has also been proposed as a potential factor contributing to menstrual irregularities, however consistent with other research in the area, results have been conflicting (8). In some instances, studies have shown a reduction in dietary fat intake among athletes, resulting in a shift in estrogen metabolism. However as mentioned, other reports have contradicted this finding (8). 

Ultimately, as with most metabolic outcomes in response to diet, there is a large degree of individual variability. Metabolism likely interacts with external variables such as diet and training to induce menstrual dysfunction. However, whether a chronic state of caloric insufficiency (or low energy availability, as discussed in the next section) caused by exercise results in menstrual disturbances or not is yet to be determined. Whether or not exposing the female athlete to multiple stressors (exercise, diet or weight-loss) are the causal factors that lead to an increased risk of menstrual disturbances is also unclear.

4. Energy Availability

As seen above, there exists the presence of multiple factors at play that impacts the menstrual cycle; including the amount of exercise, the intensity of exercise, body weight, body fat levels and overall caloric intake. This creates a situation whereby it is difficult to draw conclusions regarding a single factor causing menstrual disturbances among female athletes. However, the concept of energy availability (EA), which essentially ties all of these factors together, presents a potential explanation for such disturbances.  

Energy availability describes the amount of dietary energy for all physiological functions of the body after accounting for energy expended through exercise (10). Quite simply, the amount of remaining energy available for essential body functions after exercise or training (10). Energy is required by the body to keep the heart beating, brain functioning, blood circulating, it helps to build bone and sustains the function of the reproductive system. Although these processes are necessary, they are not equally important. Certain functions, such as keeping the heart beating or brain functioning are critical for an individual to stay alive. In contrast to this maintaining reproductive and immune function are not so. A reduction in these functions is not ideal, however, it is not life-threatening. External to the functions within the body, exercise is the primary activity that requires energy. 

Energy Availability = Energy Intake (kcal) – Exercise Energy Expenditure (EEE) (kcal)/ Fat Free Mass (kg)

It is important to note that EA and energy balance are not the same. Energy balance refers to the difference between calorie intake and total daily energy expenditure (11). In comparison to EA, which is the difference between calorie intake and exercise energy expenditure (11). What this means is that over time energy balance may change as the body undergoes metabolic adaptations, while EA remains the same. This is the case if calorie intake and TDEE are decreasing, but calorie intake and exercise energy expenditure are unchanged. This may lead to a situation whereby a woman may cease to lose fat or weight while her EA is unchanged and potentially too low to sustain all bodily functions, including menstruation.

A state of low energy availability (LEA) may result when exercise energy expenditure exceeds energy intake, as may occur in endurance sports or aesthetics sports, such as ballet, bodybuilding and gymnastics, but may also present when energy intake is reduced more than exercise energy expenditure, such as during calorie restriction (10). Essentially, there is a mismatch between an athlete’s intake (diet) and the energy expended in exercise, which leaves an insufficient amount of energy to support the essential functions of the body to maintain optimal health and performance (12).

As energy availability falls, there are several negative physiological changes that occur in the female body. The primary one being a reduction in LH levels in conjunction with a reduction of the pattern of its release, termed LH pulsatility (12). In addition to this, the body will undergo other hormonal changes in its efforts to conserve energy. These include reduced insulin, leptin and active thyroid levels in conjunction with increased cortisol and growth hormone levels (12). 

Studies have shown that when caloric intake is maintained at maintenance levels, LH pulsatility remains unchanged during periods of strenuous exercise. Quite simply, the negative impact on menstrual cycle function induced by exercise stress is the result of a low EA state, as opposed to the effect of exercise itself. Further to this, as little as 5 days of low EA is enough to produce measurable reductions in LH pulsatility, insulin, leptin and active thyroid hormone levels and an increase in cortisol (13). It is unlikely menstrual cycle function will become disrupted in this time frame, however, the hormonal adaptations are quick to occur. Over time, such hormonal changes may result in significant menstrual cycle disturbances, such as amenorrhea, and would likely be accompanied by a multitude of hormonal effects. 

As you can see the possible causes of menstrual cycle disturbances are many, and the consequences of such, both physical and psychological, have the potential to significantly impact an athlete’s ability to perform and ultimately may end their career. An awareness among both athletes and coaches is essential to assist in addressing such issues and putting appropriate measures in place to manage athletes who present with these disturbances.

References

1. Lieberman JL, MJ De Souza, DA Wagstaff et al. Menstrual disruption with exercise is not linked to an energy availability threshold. Med Sci Sports Exerc. 2019, 50 (3): 551-561.

2. De Souza MJ, J Schneid, RJ Mallison, et al. High prevalence of subtle and severe menstrual disturbances in exercising women: Confirmation using daily hormone measures. Hum Reprod. 2010, 25 (2): 491-503.

3. Lagowska K, K Kapczuk, Z Friebe, et al. Effects of dietary intervention in young female athletes with menstrual disorders. J Int Soc Sports Nutri. 2014, 21.

4. Dadgostar H, M Razi, A Aleyasin, et al. The relation between athletic sports and prevalence of amenorrhea and oligomenorrhea in Iranian female athletes. BMC Sports Sci. Med. Rehabilitation. 2009, 16.

5. Gasner A, A Rehman. Primary amenorrhea. StatPearls Publishing. 2020. https://www.ncbi.nlm.nih.gov/books/NBK554469/

6. Master-Hunter T, DL Heiman. Amenorrhea: Evaluation and treatment. Am Fam Physician. 2006, 73(8): 1374-1382.

7. Fruth SJ, TW Worrell. Factors associated with menstrual irregularities and decreased bone

mineral density in female athletes. J. Orthop. Sports. Phys. Ther. 1995, 22(1): 26-39.

8. Benson JE, KA Engelbert-Fenton, PA Eisenman. Nutritional aspects of amenorrhea in the female athlete triad. Int. J. Sport Nutr. 1996, 6: 134-145.

9. De Souza MJ, DK Lee, JC VanHeest, et al. Severity of energy-related menstrual disturbances increases in proportion to indices of energy conservation in exercising women. Fertil Steril. 2007, 88 (4): P971-975.

10. Márquez S, O Molinero. Energy availability, menstrual dysfunction and bone health in sports; an overview of the female athlete triad. Nutr. Hosp. 2013, 28 (4): 1010-1017.

11. Areta JL. HL Taylor, and K Koehler. Low energy availability: history, definition and evidence of its endocrine, metabolic and physiological effects in prospective studies in females and males. Eu. J Appl Physiol. 2020.

12. Mountjoy M, JK Sundgot-Borgen, LM Burke, et al. IOC consensus statement on relative energy deficiency in sport (RED-S): 2018 update. Br J Sports Med. 2018.

13. Loucks AB, JR Thuma. Luteinizing hormone pulsatility is disrupted at a threshold of energy availability in regularly menstruating women. J. Clin. Endocrinol. Metab. 2003, 88 (1): 297-311.