Sleep is generally recognized as a critical factor in athlete performance. Sleep is believed to affect physiological and cognitive function, which can affect sports performance. Recent evidence suggests that athletes experience lower quality of sleep, as well as lower quantity of sleep, compared to non-athletes, particularly during periods of intensified training.

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Lack of sufficient sleep will likely have detrimental effects on athletic performance. Impaired sleep can also influence cognition, learning, memory, pain perception, immunity and inflammation. Chronic partial sleep deprivation can result in changes in carbohydrate metabolism, protein synthesis, appetite and food intake. These factors can ultimately have a negative influence on an athlete's nutritional, metabolic and hormonal status and therefore could potentially reduce athletic performance.

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Several neurotransmitters (e.g., 5-HT, gamma-aminobutyric acid, orexin, melanin-concentrating hormone, norepinephrine, and histamine) have been associated with the sleep-wake cycle. There are some nutritional interventions that can influence these neurotransmitters in the brain and therefore can influence sleep. For example, carbohydrates, tryptophan, valerian, melatonin and others have been investigated as possible sleep inducers and represent promising potential interventions to improve the quantity and/or quality of sleep.

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The synthesis of 5-HT in the brain is dependent on the availability of its precursor, the amino acid tryptophan (Trp). Trp is transported across the blood-brain barrier by a transport system that is shared by the large neutral amino acids (LNAA), including the branched-chain amino acids (the BCAAs) leucine, isoleucine, and valine. Thus, the Trp/LNAA ratio in the blood is crucial for the rate of Trp transport to the brain. Protein intake generally decreases Trp uptake into the brain, as Trp is the least abundant amino acid and therefore other LNAA are preferentially transported to the brain. Carbohydrate ingestion, however, increases brain Trp, as the increase in circulating insulin (as a result of increased blood glucose concentration) stimulates the uptake of LNAA in skeletal muscle, which results in an increase in free Trp in the brain. circulation, an effect that promotes its absorption in the brain.

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There are numerous investigations into the effects of tryptophan supplementation on sleep, and it appears that doses of Trp as low as 1g can improve sleep latency (time before falling asleep) and subjective sleep quality.

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Melatonin is a hormone that influences the sleep-wake cycle, inducing a sleep-promoting effect. Light exposure to the retina of the eyes results in a suppression of melatonin secretion. Some nutritional interventions that increase Trp availability or reduce plasma LNAA concentration may increase melatonin production and promote sleep. This can be achieved through several means:

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Another recently investigated nutritional supplement is tart cherry juice, which contains relatively large amounts of phytochemicals, including melatonin. Ingestion of tart cherry juice showed an increase in urinary melatonin, and when consumed over a period of one week it resulted in improvements in sleep time and quality compared to placebo.

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Recent studies on the effects of carbohydrate intake on sleep quality and quantity indicate that carbohydrate-rich meals consumed 1 hour before bed improve sleep quality and reduce wakefulness. Solid meals compared to liquids tend to reduce sleep onset latency (time needed to fall asleep) up to 3 hours after ingestion, and a high glycemic index (GI) meal, if consumed 4 hours before bedtime, significantly reduces sleep latency. onset of sleep. In other words, solid meals with a high glycemic index, when consumed 3-4 hours before bed, help to "fall asleep".

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Some studies have investigated more chronic manipulations of habitual food intake during sleep and have suggested that diets richer in carbohydrates result in faster sleep onset, diets richer in protein result in fewer episodes of wakefulness, and diets rich in fat may negatively influence total sleep time.

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Other suggested sleep aids have not been adequately investigated and are not supported by scientific evidence: passionflower, kava, St. John's wort, lysine, glycine, magnesium, lavender, skullcap, lemon balm, magnolia bark, and nucleotides. Many of these can be found in supplements that are claimed to improve the quantity and/or quality of sleep.

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Current practical recommendations for improving sleep through nutritional interventions include:

It is important to note, however, that research in this area is limited and more work is needed before firm conclusions can be drawn.

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References: Silber BY, Schmitt JA. Effects of tryptophan loading on human cognition, mood, and sleep. Neurosci Biobehav Rev. 34(3):387-407, 2010.

Buscemi N, Vandermeer B, Hooton N, Pandya R, Tjosvold L, Hartling L, Baker G, Klassen TP, Vohra S. The efficacy and safety of exogenous melatonin for primary sleep disorders. The meta-analysis. J Gen Intern Med. 20(12):1151-8, 2005.

Howatson G, Bell PG, Tallent J, Middleton B, McHugh MP, Ellis J. Effect of tart cherry juice (Prunus cerasus) on melatonin levels and enhanced sleep quality. Eur J Nutr. 51(8):909-16, 2012.

Fernández-San-Martín MI, Masa-Font R, Palacios-Soler L, Sancho-Gómez P, Calbó-Caldentey C, Flores-Mateo G. Effectiveness of Valerian on insomnia: a meta-analysis of randomized placebo-controlled trials. Sleep Med. 11(6):505-11, 2010.