Young female athletes face endocrine changes, including menstrual disorders and peak bone mass, that are related to intense exercise. Endocrine changes related to intense training were examined in a recent review published in the Journal of Clinical Endocrinology & Metabolism.1
Intense training during adolescence, especially when associated with undernutrition, weight loss and low BMI, affects sex hormones, the adrenal axis, adipose tissue-related hormones, gastrointestinal peptides, the growth hormone (GH) axis and the thyroid axis.
To explore these effects, the authors of this review examined articles in the Medline database that were published between 1990 and 2013, 87 of which were included in the analysis.
Factors Affecting Endocrine Health of Female Athletes
Reproductive dysfunction related to exercise may have an impact on growth velocity and the acquisition of peak bone mass. Adipose tissue and energy balance have endocrine roles that regulate homeostasis and reproductive function.
Leptin, which is likely to have roles in initiating and sustaining menses, has been the focus of much research in this area. It is “significantly decreased in young athletes,” wrote the authors, and this decrease is observed both in sports involving strict weight control and in team sports. Other hormones of interest include adiponectin, visfatin, ghrelin, peptide YY, insulin-like growth factor-1 (IGF-1) and total triiodothyronine (T3).
Between 4% and 66% of young women athletes experience menstrual dysfunction, with the prevalence depending on the type, intensity and duration of the sports practice. The prevalence is highest in sports emphasizing leanness or low body weight. These sports include running, gymnastics and ballet, though other sports that have fewer nutritional constraints, such as swimming, were also found to be affected.
Physical exercise also affects peak bone mass, which influences both mechanical loading and hormonal regulation. Because bone mass increases rapidly during puberty, hormonal disorders are detrimental to peak bone mass.
While menstrual disorders are known to be associated with decreased bone mass in untrained adolescents, teen athletes are also often mechanically loading their bones. Overall, the final result is “a subtle equilibrium between these two components that is greatly dependent on the nature of the sport and the bone site evaluated,” explained the authors.
Exercise does not appear to alter bone turnover, though significantly higher levels of a bone resorption marker and lower levels of a bone formation marker and of osteoprotegerin have been observed in female athletes with amenorrhea vs. those with normal menstrual cycles. These markers were more sensitive than dual-energy x-ray absorptiometry (DXA) at detecting favorable changes of bone to the resumption of menses in young athletes with amenorrhea.
A deficiency in bone mass acquisition is unlikely to be compensated after intense training ceases or is reduced, the authors found.