What sets the female gender apart most from the male is the dynamic rhythmicity of the reproductive cycle. Dynamic fluctuations in hormone levels cyclically prepare the female human body for propagation of the species despite the volitional intent to produce children. Today, more women are participating in sports activities and training has become increasingly intense. Consequently, the effect of exercise and nutrition on women’s reproductive and metabolic physiology has become an important aspect of sports pathology. What happens to women’s bodies when the ever-changing circus of hormones is altered by exercise and diet?
Many female bodybuilders are familiar with irregularities in their menstrual cycles as they prepare for competition. Some women experience only a short-term loss of the bleeding; others may not have a normal menstrual cycle for nearly a year. Others may experience irregular and frequent bleeding. However, these menstrual dysfunctions are not relegated to female bodybuilders. The literature cites numerous studies of menstrual irregularities in other female athletic endeavors such as ballet, swimming, tennis, powerlifting, sprinting, skiing, cycling, marathon running and others. Over twenty years of research and an abundance of articles have provided increasing insight and several hypotheses on the basis of the phenomenon. In this column, we will take a look at what causes menstrual dysfunction and the associated health risks.
The primary menstrual dysfunction is amenorrhea, or lack of menstruation. One of the major problems in the relevant literature is inconsistency in defining the term ‘amenorrhea’. The criteria has included:
- one menstrual period during the last ten months,
- less than three menstrual cycles per year,
- the absence of periods from 3-12 months.
Despite the inconsistencies in the literature, amenorrhea occurs nearly 20 times more frequently in female athletes compared to the general population. According to a recent review of the literature, amenorrhea is reported to exist in up to 50% of female athletes.
Etiology of Amenorrhea
Although several hypotheses exist describing the mechanisms causing amenorrhea, most authors agree that it is a dysfunction at the hypothalamic level and consequently is referred in the literature as ‘functional hypothalamic amenorrhea.’ A small section of tissue in the brain, the hypothalamus, secretes several hormones that control the release of other hormones throughout the body. Pulsatile secretion of gonadotropin releasing hormone (GnRH) from the hypothalamus regulates the release of the gonadotropins: luteinizing hormone (LH) and follicle stimulating hormone (FSH). These hormones are released from the pituitary and in turn regulate release of other hormones, such as estrogen from the ovaries.
Studies have established that release of GnRH is suppressed as well as LH levels in women with non-pathogenic amenorrhea. Since pulsatile secretion of gonadotropins is required for initiating ovulation, any disturbance in the secretion of GnRH will affect ovulation and menstrual cycles. Where the inconsistencies exist amongst authors is in the hypotheses to explain why the GnRH pulse is dysfunctional. A summary of these hypotheses follows.
Body Fat Composition
A popular mechanism proposed in the sports circles for amenorrhea is low body fat. Although low body fat is indeed commonly associated with amenorrhea and menstrual cycle irregularities, the research has not conclusively proven that there is a ‘critical level’ of body fat necessary to maintain regular cycles. As well, female athletes with adequate body fat may still experience menstrual irregularities. Conversely, many very lean athletes do not experience amenorrhea. The rate of body mass loss may be more critical than the absolute amount of body fat lost. After all, muscle tissue and the skeleton, not just body fat, also determine the total body mass. Therefore, alterations in both lean body mass and body fat may be important in concluding if a critical body fat level is a valid hypothesis for causing amenorrhea.
Some authors propose that amenorrhea may be a consequence of dietary restriction or weight loss. Some correlations are seen in athletes with diets low in fat and lack of carbohydrate intake. While this may definitely be seen in females with thyroid disease or severe eating disorders, it is still uncertain whether this is solely responsible for amenorrhea in otherwise healthy female athletes. However, it is well demonstrated in both animals and humans that specific nutrition, such as vegetarian diets, can induce changes in hormone levels.
Weight loss is also associated with amenorrhea because many female athletes are below or near their purported ‘ideal weight’ determined by body fat and the body mass index. As mentioned previously, the actual rate of body mass loss rather than the amount of loss may be more important. Although amenorrhea may be associated with weight loss, a nutritional deficiency (such as in a low fat diet) which leads to body fat loss or brings on menstrual irregularities may be responsible.
Training Volume and Intensity
Increasing evidence demonstrates a relationship between training volume and menstrual irregularities. Many authors now term the syndrome as exercise-related menstrual irregularities (ERMI) or exercise-induced amenorrhea. While short-term exercise elicits a transient change in some hormone levels, prolonged and extreme endurance exercise induces significant changes in gonadotropin plasma levels and additional hormones. Other mechanisms that occur with exercise such as lower ovarian blood circulation, an increase in metabolism and changes in metabolic clearance rate of endogenous hormones may also contribute to menstrual irregularities.
Studies of women weightlifters showed few alterations in most hormone levels. However, one study showed significant increases in gonadotropins, cortisol and testosterone. Many inconsistencies in the studies exist due to cycle phase during the studies and conflicting data. As well, few of the studies take into consideration medications or drugs that may alter hormonal levels, such as anabolic steroids or oral contraceptives.
Ultimately, most authors agree that a critical metabolic or ‘energy balance’ is a major regulator of GnRH regulation. Evidence suggests that physical stress resulting from acute exercise and chronic caloric restriction is most responsible for menstrual irregularities. Several studies document changing eating habits and exercise patterns reverse ERMI.
Menstrual irregularities in female athletes are most likely induced by several integrated factors, which are presented above. Most likely, ERMI is caused by a feedback effect of changes in estrogen levels. The literature describes well that long term exercise alters sex steroid metabolism. Such alterations can be attributed to changes in metabolic clearance rate as influenced by diet constituents or medications. Alterations can also be provoked by changes in aromatization resulting from decreased body fat. Additionally, a diet low in fat or a diet low in calories may potentiate altered steroid levels and thus affect GnRH secretion.
Use of specific anabolic steroids (nandrolone, oxymetholone and ethylestrenol) in women are known to inhibit ovulation and induce amenorrhea. Other steroids (oxandrolone, stanozolol, metandienone and fluoxymesterone) have been shown to have no such effects in women. However, these studies were administered in recommended pharmaceutical dosages, which may be 20-50 times less than the large dosages used by some female athletes. No studies have elucidated the possible synergistic effects of anabolic steroids and high-intensity training coupled with caloric restriction typical of many female bodybuilders.
Anecdotal testimony relayed to me confirms that most competitive female bodybuilders experience short to long-term periods of amenorrhea due to several factors that have been already discussed. Some women also report weeks of frequent bleeding before regular menstrual cycles resume. Although most of the affected athletes enjoy the reprieve from menstruation, health risks may be associated with long term amenorrhea and should be a cause of concern.
Long term menstrual irregularities are known to have detrimental effects on bone mineral status and fertility. While there is little evidence of harmful effects of ERMI on reproductive status, the most serious risk is the impact on the skeleton. Osteoporosis and increased risk for stress fractures are of major concern and have been fully documented in the literature.
Long term amenorrhea may result in low bone density at multiple skeletal sites, especially the spine. Even skeletal sites subjected to impact loading during exercise failed to mineralize bone. Studies also show that bone mineral loss is sustained even after resumption of regular menstrual cycles. Nor did high calcium intake compensate for lack of bone accumulation.
There is no research that indicates that bone loss is negated in female athletes using anabolic steroids and presenting with amenorrhea. Hormone replacement therapy at dosages used for postmenopausal women have not been effective in increasing bone mass in athletes with long-term amenorrhea. However, such therapy may help protect against further bone loss. Oral contraceptives have been successful in some cases and unsuccessful in others to restore menstruation in training athletes. Although more research is needed, high doses of hormones may be required to prevent bone loss and restore menstruation.
Be aware that amenorrhea may persist and take up to 6 months to reverse. Treatment methods may be discovered that will maintain peak bone mass without the need for reducing athletic training intensity or interfering with performance. Until that time, ensure adequate nutrient intake to meet energy requirements and adjust training schedules to include short periods of lower intensity. Additionally, oral contraceptives may be utilized to maintain menstruation cyclicity and suppress frequent bleeding.
If body fat reduction is imperative, such as in preparing for a bodybuilding competition, consult with a physician to discuss methods to prevent amenorrhea. In addition to the above mentioned interventions, amenorrhea may be avoided by including fats in the diet and slowly reducing body fat while minimizing loss of total body mass. Moderation in cardio activity may also be beneficial. Since it is not clear whether it is possible to restore bone loss with continuation of training, the best approach is to prevent long-term ERMI.