Research on the relationship of nutrition and sleep is ever growing. Why? Sleep disturbances and short sleep duration are behavioral risk factors for inflammation, associated with increased risk of illness and disease (1). Sleep is meant to have a restorative effect on the body, and for this to occur to its fullest potential, it must be of adequate duration and quality, especially for athletes whose physical and mental recovery needs may be greater due to the high physiological and psychological demands during training and competition (1). Various nutritional interventions have been shown to improve sleep including high carbohydrate, high glycaemic index evening meals + tryptophan rich protein, melatonin, antioxidant rich tart cherry juice and kiwifruit, magnesium, and B vitamins (1). Functional food-based interventions designed to enhance sleep quality and quantity or promote general health, sleep health, training adaptations and/or recovery warrant further investigation (1).
Tryptophan is an essential amino acid that is a precursor to serotonin and melatonin, which can cross the blood-brain barrier by competing for transport with other large neutral amino acids (LNAA). Carbohydrates affect plasma tryptophan:LNAA ratio and may compliment the sleep enhancing effect of consuming tryptophan rich protein. Consumption of high glycaemic index (GI) carbohydrate increases the ratio of circulating tryptophan:LNAA via direct action of insulin which promotes muscle uptake of LNAA, thus increasing tryptophan availability for synthesis of serotonin and ultimately melatonin (2). A high GI meal consumed four hours before bed, significantly reduced sleep onset latency, compared to a low GI meal (3).
Magnesium is believed to enhance melatonin secretion, promoting sleep onset, and act as a main inhibitory neurotransmitter that acts on the central nervous system (CNS) (4). Magnesium is important for the production of the enzyme N-acetyltransferase which converts 5-HT into N-acetyl-5-hydroxytryptamine, which can then be converted to melatonin (3).
Vitamin B12 contributes to melatonin secretion, pyridoxine (vitamin B6) is involved in the synthesis of serotonin from tryptophan and niacin (vitamin B3) may elicit a tryptophan sparing effect (4). Folate (vitamin B9) and pyridoxine are involved in the conversion of tryptophan into serotonin (2).
Antioxidant consumption may influence recovery from exercise but may also influence sleep since sleep regulation is influenced by pro-inflammatory cytokines (5). Dietary antioxidants (e.g., vitamin C and vitamin E) augment endogenous antioxidant content within skeletal muscle (5). Tart cherries contain high concentrations of melatonin and a range of phenolic compounds that have both antioxidant and anti-inflammatory properties (6). A recent study was conducted to investigate the effect of tart cherry juice (2 × servings of 30 mL concentrate) on sleep enhancement, sleep duration and sleep quality (6). This was the first investigation to demonstrate that tart cherry juice supplementation increased circulating melatonin levels and improved sleep time and quality in healthy adults. In the intervention group tart cherry juice supplementation resulted in significantly elevated total melatonin content, increased time in bed (+24 min), increased total sleep duration (+34 min) improved sleep efficiency total (82.3%) and a significant reduction in daytime napping (–22%) (6). Kiwifruit are nutritionally dense containing a range of nutrients that can benefit sleep, health and recovery including serotonin, vitamin C, vitamin E, vitamin K, folate, anthocyanidins, carotenoids, beta-carotene, lutein, potassium, copper and fibre (7). A study involving volunteers with a self-reported sleep disturbance demonstrated consumption of two kiwifruit one hour before bedtime for four weeks significantly improved actigraphy-measured total sleep duration and sleep efficiency (7).
Based on the existing scientific literature there appears to be considerable scope for further investigation of nutrition interventions designed to enhance sleep quality and quantity or promote general health, sleep health, training adaptations and/or recovery in both general and athletic populations; as it has been showcased nutrients such as antioxidants, tryptophan rich protein and carbohydrate, melatonin, magnesium and micronutrients/fruit can affect sleep (4). Healthy sleep habits should also be considered when attempting to optimize sleep quality and duration.
References:
1. Doherty, Rónán, et al. "Sleep and nutrition interactions: Implications for athletes." Nutrients 11.4 (2019): 822.
2. Ordóñez, F.M.; Oliver, A.J.S.; Bastos, P.C.; Guillén, L.S.; Domínguez, R. Sleep improvement in athletes: Use of nutritional supplements. Am. J. Sports Med. 2017, 34, 93-99.
3. Afaghi, A.; O’connor, H.; Chow, C.M. High-glycemic-index carbohydrate meals shorten sleep onset. Am. J. Clin. Nutr. 2007, 85, 426–430. [CrossRef] [PubMed]
4. Peukhuri, K.; Sihvola, N.; Korpela, R. Diet promotes sleep duration and quality. Nutr. Res. 2012, 32, 309–319. [CrossRef] [PubMed]
5. Nieman, D.C.; Mitmesser, S.H. Potential Impact of Nutrition on Immune System Recovery from Heavy Exertion: A Metabolomics Perspective. Nutrients 2017, 9, 513. [CrossRef] [PubMed]
6. Bell, P.; Stevenson, E.; Davison, G.; Howatson, G. The effects of Montmorency tart cherry concentrate supplementation on recovery following prolonged, intermittent exercise. Nutrients 2016, 8, 441. [CrossRef] [PubMed]
7. Lin, H.H.; Tsai, P.S.; Fang, S.C.; Liu, J.F. Effect of kiwifruit consumption on sleep quality in adults with sleep problems. Asia Pac. J. Clin. Nutr. 2011, 20, 169–174.
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