Diet promotes sleep duration and quality Katri Peuhkuri ⁎ , Nora Sihvola, Riitta Korpela Institute of Biomedicine, Pharmacology, Medical Nutrition Physiology, University of Helsinki, PO Box 63, FIN-00014, Helsinki, Finland ARTICLE INFO ABSTRACT Article history: Received 4 October 2011 Revised 13 March 2012 Accepted 20 March 2012 Sleep, much like eating, is an essential part of life. The mechanisms of sleep are only partially clear and are the subject of intense research. There is increasing evidence showing that sleep has an influence on dietary choices. Both cross-sectional and epidemiologic studies have demonstrated that those who sleep less are more likely to consume energy- rich foods (such as fats or refined carbohydrates), to consume fewer portions of vegetables, and to have more irregular meal patterns. In this narrative review, we pose the opposite question: can ingested food affect sleep? The purpose of this review is to discuss the evidence linking diet and sleep and to determine whether what we eat and what kind of nutrients we obtain from the food consumed before bedtime matter. In addition, scientific evidence behind traditional sleep-promoting foods such as milk and some herbal products is briefly described. These are reviewed using data from clinical trials, mostly in healthy subjects. In addition, we discuss the possible mechanisms behind these observations. Lastly, we summarize our findings that emerging evidence confirms a link between diet and sleep. Overall, foods impacting the availability of tryptophan, as well as the synthesis of serotonin and melatonin, may be the most helpful in promoting sleep. Although there are clear physiological connections behind these effects, the clinical relevance needs to be studied further. © 2012 Elsevier Inc. All rights reserved. Keywords: Sleep Diet Food Nutrients Protein Tryptophan 1. Introduction Sleep is a physical and mental resting state, in which a person becomes relatively inactive and unaware of their environ- ment. The purposes and mechanisms of sleep are only partially clear and are the subject of intense research [1,2]. Sleep is considered adequate when there is no daytime sleepiness or dysfunction. The amount of sleep a person needs varies individually and depends on various factors, one of which is age. Most adults need about 7 to 8 hours of sleep per day, but infants and teenagers need more [3]. With age, sleep latency, sleep arousals, and awakenings as well as reductions in sleep duration increase, although decline in nighttime sleep duration is paralleled by an increase in napping during the daytime [4]. Sleep is controlled by the circadian clock, sleep-wake homeostasis, and willed behavior. Sleep duration can be measured with fairly simple methods. Subjective methods include a sleep diary and validated questionnaires, whereas electroencephalogram, polysomno- graphy, and actigraphy measurements provide more objective results. Other parameters to define sleep, such as the subjective experience of sleep quality, are more complicated because even the term “sleep quality” has not been rigorously defined [5]. NUTRITION RESEARCH 32 (2012) 309 – 319 Abbreviations: 5-HTP, 5-hydroxytryptophan; AADC, aromatic L-amino acid decarboxylase; CCK, cholecystokinin; E%, percent of total energy intake; GABA, γ-aminobutyric acid; LNAA, large neutral amino acid; PYY, peptide tyrosine-tyrosine; REM, rapid eye movement; TDO, tryptophan 2,3-dioxygenase; TRP, tryptophan. ⁎ Corresponding author. Tel.: +358 9 191 25 366; fax: +358 9 191 25 364. E-mail address: katri.peuhkuri@helsinki.fi (K. Peuhkuri). 0271-5317/$ – see front matter © 2012 Elsevier Inc. All rights reserved. doi:10.1016/j.nutres.2012.03.009 Available online at www.sciencedirect.com www.nrjournal.com