LOUCKS, A. B. Introduction to Menstrual Disturbances in Athletes. Med. Sci. Sports Exerc., Vol. 35, No. 9, pp. 1551-1552, 2003. The first symposium on this topic at an annual meeting of ACSM was presented 22 yr ago when the high prevalence of menstrual disorders in athletes was becoming increasingly apparent. The clinical consequences and need for treatment for menstrual disturbances in athletes have been recognized by ACSM through the publication of its 1997 Position Stand on the Female Athlete Triad. This mini-symposium presents an update on recent scientific advances on this topic. The first review in this symposium concentrates on a menstrual disturbance in which the length of the luteal phase is abbreviated and luteal function is suppressed. Such luteal suppression occurs in a large proportion of even the most regularly menstruating athletes. The next two papers summarize what has been learned about the mechanism of these disturbances from prospective experiments that have employed diet, exercise, cold exposure, and pharmacological blockers of metabolic pathways to disrupt menstrual cycles in monkeys and humans as well as estrous cycles and reproductive behavior in hamsters.
The purpose of this symposium was to provide the reader with a broader perspective on menstrual disorders in physically active women and to convey lessons learned from prospective experiments in animals and humans about the hypothetical causes and mechanisms of those disorders. It is hoped that these reviews will also provide the reader with a better appreciation of the methodologies necessary for gathering reliable data in this field of investigation.
The high prevalence of menstrual disorders in athletes has been recognized for 25 yr and the progressive skeletal demineralization in hypoestrogenic amenorrheic athletes for 20 yr. Although several hypotheses have been proposed to explain these disorders, no mechanism mediating the disruption of reproductive function in physically active women by environmental or behavioral factors has yet been demonstrated. Recently, I outlined the evidence favoring restricted energy availability, rather than an overly lean body composition or stress, as the most likely factor initiating menstrual disturbances in athletes (5). By energy availability, we mean the difference between dietary energy intake and exercise energy expenditure. Thus, energy availability can be restricted either by reducing energy intake alone or by increasing energy expenditure alone or by a combination of both.
Originally, restricted energy availability was implicated as the cause of menstrual disturbances in athletes by dietary surveys indicating that female athletes appeared to consume less than would be expected for their level of physical activity. Although some questioned whether respondents were merely under-reporting their dietary intake, appearances were confirmed by measurements of alterations in metabolic hormones and substrates, and by reductions in metabolic rate, in female athletes that are characteristic of energy deficiency. Such observations have been followed by demonstrations in prospective animal and human experiments that LH pulsatility and menstrual cycles can be disrupted by increasing exercise energy expenditure without reducing dietary energy intake, and that such disruptions can be prevented or reversed by dietary supplementation without moderating the exercise regimen. Thus, exercise appears to have no deleterious effect upon the reproductive system beyond the impact of its energy cost on energy availability.
The American College of Sports Medicine Position Stand on the Female Athlete Triad (6) was published in 1997 after the concept of the Female Athlete Triad as a syndrome was developed at a consensus conference held in 1992. The Triad is a morbid condition comprising some degree of inadequate eating (in the extreme, a diagnosable eating disorder), some form of menstrual disorder (in the extreme, amenorrhea), and some degree of skeletal demineralization (in the extreme, osteoporosis). In its own position stand (1), the American Academy of Pediatrics attributes the Female Athlete Triad to reduced energy availability and makes nine recommendations for medical supervision and treatment, including estrogen supplementation.
Unfortunately, estrogen supplementation alone has not been effective for increasing bone density in amenorrheic athletes (3). Because the primary role of estrogen in bone metabolism is to reduce the rate of bone resorption, this disappointment suggests that the rate of bone formation may also be impaired in these women. Indeed, nutritionally dependent bone growth factors are low in amenorrheic athletes (4), and they predict spinal and femoral neck bone mass in gymnasts and runners (7). Recently, the combined administration of recombinant human IGF-1 with a low-dose oral contraceptive increased bone density in anorexia nervosa patients with osteopenia (2). The efficacy of this pharmacological treatment for increasing bone density in amenorrheic athletes has not yet been reported.
The first review in this symposium, written by Mary Jane De Souza, concentrates on another type of menstrual disturbance in which the length of the luteal phase is abbreviated and luteal function is suppressed. Such luteal suppression occurs in a large proportion of even the most regularly menstruating athletes and is entirely imperceptible to them. It is revealed only by an endocrine evaluation.
A recent review of the short-term prospective experiments that have elucidated acute effects of restricted energy availability on the central regulation of reproductive function is available elsewhere (5). Such experiments can be tightly controlled and intensively monitored with acceptable attrition at reasonable cost to identify and quantify causal relationships between various treatment factors and luteinizing hormone (LH) pulsatility, upon which ovarian function critically depends. The second review in this symposium, written by Nancy Williams, focuses on the lessons that have been learned from longer-term prospective experiments that have investigated the effects of chronically restricted energy availability on menstrual cycling in monkeys and humans. Such prolonged experiments are necessary to confirm that acute effects on LH pulsatility are predictive of chronic effects on peripheral end-organs.
The third review in this symposium, written by George Wade, summarizes the lessons learned from the experimental disruption of estrous cycles and behaviors in other mammals. Such experiments have permitted hypotheses about the physiological and neuroendocrine mechanisms mediating the influence of energy availability on the central regulation of reproductive function to be investigated in detail.