Chrononutritional Modulation of Sleep and the Circadian Clock by Amino Acids

The daily rhythms of the sleep-wake cycle and physiologic functions are controlled by the circadian clock, which is a hierarchical system involving a central clock in the suprachiasmatic nucleus and peripheral clocks in other brain regions and organs. The circadian clock is entrained by photic and nonphotic signals, including food availability and nutrients. Numerous studies have demonstrated the modulatory effects of various nutrients, including macronutrient-derived factors and micronutrients, on the circadian clock. Several amino acids represent such functional food factors, supported by the evidence for modulation of sleep quality and related physiologic functions, sleep-wake rhythms, hormonal rhythms, and the expression of clock genes in rodents and humans. This review focuses on the functional roles of amino acids, primarily l-serine, l-ornithine, and glycine, as modulators of sleep, stress, and the circadian clock in animals and humans.