Īlthough some studies have focused on the antioxidant components and anti-inflammatory effects of milk products, it is not easy to directly explain the relationship between sleep quality and dairy intake because it may be masked by the much greater effect of diet as a whole. Therefore, beverages in which milk has been sweetened with sugar additives (e.g., malted milk products such as Horlicks) have been produced and are now being advertised and marketed as sleep aids. An increased amount of Try passes through the BBB when blood glucose concentration is high. As the BBB transporter is shared by the large, neutral amino acid LNAA (tryptophan (Try), phenylalanine (Phe), valine (Val), leucine (Leu), isoleucine (Ileu), tyrosine (Tyr)), Try transfer into the brain is determined by the Try/LNNA ratio. Furthermore, the amino acid composition of α-lactalbumin allows Try to cross the blood-brain barrier (BBB). The α-lactalbumin protein contained in milk has the highest Try content among the food proteins normally consumed by humans. Melatonin is synthesized in vivo from Try via serotonin synthesis. īlood melatonin levels are synchronized by circadian rhythms, and this hormone induces sleep onset in humans. The anti-inflammatory effects of milk and dairy products, due to their containing antioxidant and anti-inflammatory components, as well as activity changes within the brain-gut-microbiome axis, has recently garnered extensive attention in the literature. As for the mechanism of action, it is believed that a high amount of tryptophan (Try), from which melatonin is synthesized, contained in milk and dairy products can suppress the action of the inhibitory neurotransmitter gamma-aminobutyric acid (GABA). The intake of milk and dairy products is generally considered to promote good sleep quality and to have a positive effect on physical and mental health. Overall, these studies indicated that a well-balanced diet that includes milk and dairy products is effective in improving sleep quality, despite mixed results across studies attributable to differences in study populations and methods. Four studies targeted older adults, three included toddlers, two targeted children, and six enrolled adults inclusive of university students. As a result, a total of 14 studies published between 19 were included in this review, including eight randomized controlled trials, two experimental studies with cross-over designs, one longitudinal study, and three cross-sectional studies. The following keywords were chosen as electronic database search items from MeSH (medical subject headings) terms and descriptors in health sciences (DeHS) lists: milk, yogurt, dairy product, cheese, sleep, human, observational study, and interventional study. This systematic review was conducted according to the preferred reporting items for systematic reviews and meta-analyses (PRISMA) guidelines. ![]() The present study aimed to summarize this literature and provide a unified view on whether the intake of milk and dairy products affects sleep quality. Such investigations have varied in terms of their geographic locations, amounts of milk and dairy products, study participants (age, sex, race), and study designs. ![]() ![]() Several studies have assessed the effects of milk and dairy product intake on sleep quality and duration.
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