The menstrual cycle is a complex biological process driven by the rhythmic fluctuation of hormones, primarily estrogen and progesterone. These hormones signal the lining of the uterus to thicken in preparation for pregnancy. If the egg released during ovulation is not fertilized, hormone levels drop, signaling the body to shed the uterine lining, known as menstruation. While some may assume intense exercise halts menstruation, a regular cycle is actually a key indicator of health in a female athlete. Its absence signals a significant energy imbalance within the body.
The Baseline: When the Cycle Functions Normally
Most female athletes who are adequately nourished and rested will experience a regular menstrual cycle. A regular cycle typically occurs every 24 to 38 days. Having a period is considered a vital sign of hormonal health, indicating that the body has sufficient energy to support reproduction alongside the demands of training.
The fluctuations of reproductive hormones throughout the cycle do not consistently impair athletic performance, and many elite athletes maintain or even enhance performance across various phases. While some athletes perceive symptoms like cramping, bloating, or fatigue as negatively impacting their training, studies show that Olympic gold medals have been won in every phase of the cycle. For the healthy athlete, the body is capable of managing the training load and the reproductive demands simultaneously.
When the Cycle Stops: Defining Exercise-Induced Amenorrhea
Menstrual dysfunction in athletes is a spectrum that includes oligomenorrhea, defined as irregular or infrequent periods (cycles longer than 38 days), and amenorrhea, the complete absence of menstruation for three months or more. This condition is most often functional hypothalamic amenorrhea, meaning the brain’s reproductive control center has shut down. Suppression is driven by low energy availability (LEA), where energy consumed is insufficient to cover energy expended through exercise and basic metabolic needs.
When the body perceives an energy deficit, it prioritizes survival over reproduction. The hypothalamus, a region in the brain, responds by suppressing the release of Gonadotropin-Releasing Hormone (GnRH). This suppression then prevents the pituitary gland from releasing the downstream reproductive hormones, Luteinizing Hormone (LH) and Follicle-Stimulating Hormone (FSH).
The resulting drop in LH and FSH halts normal ovarian function, preventing ovulation and the production of sex hormones like estrogen and progesterone. The lack of hormonal signals needed to build and shed the uterine lining ultimately causes the cessation of the menstrual period. This reproductive shutdown is not caused by the intensity of exercise itself, but rather by the chronic imbalance between high energy expenditure and inadequate caloric intake.
Long-Term Health Risks of Cycle Loss
The absence of a period due to low energy availability leads to a state of hypoestrogenism, meaning abnormally low levels of circulating estrogen. Estrogen plays a role in maintaining bone health by regulating bone turnover. Without sufficient estrogen, the balance shifts toward bone breakdown, leading to a rapid loss of bone mineral density (BMD). This loss can result in osteopenia or osteoporosis, even in young athletes, significantly increasing the risk of stress fractures and potentially compromising peak bone mass for life.
Menstrual dysfunction is one component of a broader clinical framework known as Relative Energy Deficiency in Sport (RED-S). RED-S is a syndrome affecting multiple physiological systems when the body is chronically under-fueled. Beyond reproductive and skeletal health, the energy deficit impairs metabolic rate, immune function, and cardiovascular health.
Specifically, the hormonal and metabolic changes can negatively affect the cardiovascular system, including elevated levels of low-density lipoprotein (LDL) cholesterol and impaired function of the blood vessels. The suppression of the menstrual cycle is a sign of this systemic energy deficiency, which can also lead to chronic fatigue, mood disturbances, and an increased risk of illness. Addressing the underlying energy issue is therefore necessary to mitigate these long-term health consequences.
Nutritional and Medical Strategies for Recovery
The treatment for restoring a regular menstrual cycle is to correct the energy imbalance. This primarily involves increasing energy intake, decreasing energy expenditure through reduced training volume or intensity, or a combination of both to achieve a positive energy balance. The goal is to signal to the hypothalamus that the body is no longer in a state of energy crisis.
Athletes should consult with a sports dietitian to develop a plan for increasing caloric intake, focusing on adequate carbohydrates and protein to support training and recovery. Monitoring and adjusting the timing of nutrient intake, especially around workouts, is a practical strategy to improve energy availability. A physician should also be involved to conduct a hormonal and nutritional assessment.
It is generally not recommended to use oral contraceptives (OCs) as the first-line treatment to “bring back” a period. While OCs can cause withdrawal bleeding, they mask the underlying energy deficit and do not restore the body’s natural hormone production or reverse the bone mineral density loss caused by the energy deficiency. Recovery is confirmed by the spontaneous return of a natural, ovulatory menstrual cycle, which signals that the body’s energy status and hormonal signaling have been successfully restored.