Sleeping sporting beauties: Part I - how hormones influence sleep

Introduction

Sleep is a key element to peak athletic performance⁽¹⁾. It is regarded as one of the most effective recovery strategies and plays an integral role in the adaptive and recuperative processes⁽²⁾. However, the recovery process is only optimal when sleep quantity and quality are adequate. High training volumes, competition demands, and exposure to numerous, ever-changing environmental factors may cause sleep impairments among elite-level athletes⁽³⁾. Physiological factors unique to female athletes, such as fluctuating sex hormone levels throughout the menstrual cycle (MC), are additional culprits that influence the quality and quantity of sleep⁽⁴⁾.

The female MC is superimposed on the circadian rhythm responsible for the sleep-wake cycle⁽⁵⁾. Additionally, hormones related to physical and psychological stressors and those responsible for sexual maturation during adolescence can further amplify sleep impairment among female athletes. Thus, understanding female athletic development is critical to fully comprehend the cascade of possible collisions that could block the road to a peaceful night’s sleep.

Circadian rhythm and athlete stressor hormones

Numerous hormonal responses take place in the lead-up to and during sleep. Growth hormone (GH) is responsible for muscle growth, repair, and bone building. It is produced throughout the day, and 95% is released during non-rapid eye movement sleep (NREM)⁽²⁾. Exercise is a physiological stressor that results in the release of cortisol and testosterone⁽³⁾. While cortisol is a catabolic hormone, i.e., it stimulates the breakdown of molecules and energy production, testosterone is an anabolic hormone, i.e., stimulates growth and repair. The balance and timing of these hormones are essential for muscle adaptation, growth, and restoration. Growth hormone,  cortisol, and testosterone follow the circadian rhythm. Sleep deprivation results in increased cortisol levels and affects the secretion pattern of testosterone and GH, ultimately disturbing the anabolic-catabolic patterns^(2,3). During sleep debt, the shift in catabolic hormones contributes to muscle mass loss and reduced muscle recovery⁽⁴⁾. In response to exercise and sleep deprivation, the fluctuations in hormonal profiles differ between athletes and non-athletes at rest.

The secretion of melatonin initiates sleep through the synchronization of environmental cues, and is suppressed by exercise⁽⁵⁾. The consequence of exercise on melatonin varies depending on the timing, length, and intensity of training sessions^(2,5). The secretion and timing of melatonin and cortisol release are inversely proportionate⁽⁶⁾. Melatonin levels are high during the biological night when cortisol levels are minimal. The opposing effects of vigorous exercise on melatonin and cortisol secretion may lead to sleep impairments among elite-level athletes (see figure 1)^(2,6).

Figure 1: The 24-hour circadian cycle release of cortisol, testosterone, and melatonin

There is conflicting evidence of the effect of the MC on both melatonin and cortisol in females⁽⁵⁾. While some evidence demonstrates no difference in melatonin levels during the luteal phase (LP) and follicular phase (FP), other researchers have found that total 24-hour melatonin secretion was significantly less during the LP than the FP. In addition, the understanding of the effect of the MC on cortisol secretion is limited.

The menstrual cycle-sleep relationship

Researchers at the McGill University in Montreal found objective sleep data indicates that females have more optimal sleep in less time awake during the night, longer sleep duration, shorter sleep latency, and greater sleep efficiency than male athletes⁽⁷⁾. However, contradictory subjective data indicates higher incidences of poor sleep among females^(5,7,8). There does appear to be a relationship between menstrual hormonal fluctuations and sleep impairments^(3,5,8). The MC phases affect the circadian rhythm in temperature, selected hormone profiles, and sleep-wake behavior^(5,8). This is due to the cyclic fluctuations of reproductive hormones that occur during a regular ovulatory MC.

Sleep impairments also occur due to symptoms associated with menstruation, including cramps, bloating, joint ache, painful breasts, anxiety, and mood changes^(4,7). In addition, fluctuating hormone levels alter females’ sleep architecture. The hormones responsible for the MC include luteinizing hormone (LH), follicle-stimulating hormone (FSH), estrogen, and progesterone (see figure 2)⁽⁶⁾.