**1. Introduction**

High-performance team-sport athletes are required to train and compete to a high standard on a weekly basis. However, these athletes face the continual challenge of balancing the physiological, neuromuscular, and psychological stressors induced by training and competition [1]. Optimizing recovery to overcome these challenges and support performance is of utmost importance [2]. Sleep plays a crucial role in recovery and has restorative effects on physiological [3], perceptual [3–5], and immune [6,7] functions. Athletes, regardless of their sport, rate sleep as their most important recovery strategy [8,9]. A reduction in sleep quality has been associated with increased incidence of fatigue-related injury [1], reductions in the skeletal muscle remodeling [10], and disturbs cellular maintenance processes [6,7]. Despite evidence affirming the importance of restorative sleep [11], elite athletes appear to experience more sleep disturbances than the general population [1,8]. Behavioral and lifestyle strategies that promote sleep and sports performance will be welcomed by athletes and coaches.

Research examining athlete sleep indicates evening competition, travel, and training schedules can have a deleterious impact on sleep quality and quantity [12]. Up to ~50% of elite athletes experience sleep disturbances following late night competition or training

**Citation:** Gratwicke, M.; Miles, K.H.; Pyne, D.B.; Pumpa, K.L.; Clark, B. Nutritional Interventions to Improve Sleep in Team-Sport Athletes: A Narrative Review. *Nutrients* **2021**, *13*, 1586. https://doi.org/ 10.3390/nu13051586

Academic Editor: David C. Nieman

Received: 23 March 2021 Accepted: 7 May 2021 Published: 10 May 2021

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sessions [1,13]. Night-time competition is widely associated with sleep issues and athletes can experience substantial disruptions (i.e., increased core temperature, muscle soreness, and delayed bedtime) to sleep quality and quantity compared with daytime competition [12]. Athletes also often face undesirable training schedules, including morning or late evening sessions, which can compromise an optimal recovery regime by reducing sleep quantity due to limited time in bed [10,12,14]. Athlete sleep quantity is also impacted by air travel, which can reduce sleep duration given a later sleep onset, delayed time in bed [15], and circadian rhythm misalignment [12]. A variety of interventions have been explored to negate the disturbances experienced by athletes, although not all have proven to be successful.

Evidence for the efficacy of interventions to improve sleep and related recovery outcomes in athletes is somewhat equivocal. Research investigating the effect of a sleep hygiene intervention in professional rugby league indicated sleep duration and efficiency increased immediately following the education seminars, but a follow-up one month later saw sleep behavior comparable to baseline levels [16]. Sleep hygiene and sleep extension interventions require athletes to change lifestyle behaviors (not always practical around training and competition schedules), which may yield poor compliance and limited effectiveness without regular follow-up [16]. Interventions that enhance athlete sleep and recovery regardless of situational changes (e.g., training times or travel demands) require further evaluation including both efficacy and practical means of implementation. Both sleep hygiene education and sleep extension interventions are effective short term, however long-term sustainability of their effects is questionable [17]. Furthermore, a recent survey study indicated female athletes may be resistant or less likely to implement sleep hygiene interventions [18]. Easily implemented techniques and strategies to improve sleep in the female athlete population are required.

It is well established that nutrition plays a vital role in performance and recovery; however, research investigating the role of selected foods, and macro- and micro-nutrients in the sleep–wake cycle is in its infancy. While the primary role of sports nutrition has been to support intensive training requirements and promote recovery [19], attention is shifting to the use of nutritional supplements for improving sleep [10]. Therefore, the aim of this review was to investigate nutritional strategies that can be utilized to enhance sleep quality and quantity, and how this information can guide future nutritional interventions focused on supporting sleep in an athletic population.
