TABLE 2.

Summary of human clinical trials testing the effects of dairy products and dairy proteins on sleep quality

Author, year	Study population	Study design	Levels of independent variable	Sleep outcome	Key findings
Fakhr-Movahedi et al., 2018 [40]	68 Iranian patients with acute coronary syndrome, aged 35–85 y, M and F	Randomized, controlled, parallel arm	Experimental: Milk (150 mL)–honey (30 g) mixture, twice/d for 3 d	Sleep quality score measured using Richards-Campbell Sleep Questionnaire at baseline and day 3	Sleep quality increased in the experimental condition; no change in control (no statistical comparison of these changes)
			Control: Patients received routine care. No beverage provided		Sleep quality at day 3 was higher in the experimental group than in the control group
Schaafsma et al., 2021 [50]	70 Dutch healthy adults, aged 30–50 y, M and F	Double-blind, placebo-controlled, randomized crossover	Experimental: 19 g of dairy whey protein and GOS-based beverage enriched with Trp (see text for more detail)	Sleep quality measured using PSQI weekly	No differences in change in sleep quality observed in an intention-to-treat analysis
			Control: 12 g of taste-matched skimmed milk powder placebo beverage	Multiple sleep dimensions measured objectively over 5 d using headband tracker at baseline and end point	In modified per-protocol analysis, at day 14, sleep quality improved in the experimental compared with that in the control group
			Experimental and placebo beverages consumed daily for 3 wk		Objectively measured REM sleep improved in the experimental group compared with that in the control group
Özcan et al., 2019 [42]	68 Turkish menopausal women with sleep complaints, aged 45–65 y, F only	Randomized controlled, parallel arm	Experimental: 500 mL kefir beverage daily for 1 mo	Sleep complaints measured using WHIIRS at baseline and end point (lower scores represent better sleep)	Sleep improved (decrease in WHIIRS score) in the experimental condition; no change in control (no statistical comparison of these changes)
			Control: No beverage provided		End point sleep scores were lower (better sleep) in the experimental vs. control
Yamamura et al., 2009 [44]	29 Japanese older healthy adults, aged 60–81 y, M and F	Double-blind, placebo-controlled, randomized crossover	Experimental: 100 g fermented milk beverage with Lactobacillus helveticus	Multiple sleep dimensions measured using wrist actigraphy over 3 wk	Sleep efficiency increased and WASO decreased in the experimental condition; no change in control (no statistical comparison of these changes)
			Control: 100 g placebo milk matched for acidity	Sleep health risk measured using Sleep Health Risk Index score at end point	No between-condition differences in end point measures
			Experimental and control beverages consumed daily for daily for 3 wk
Kinoshita et al., 2021 [52]	961 Japanese health care workers, aged 20–71 y, F only	Randomized, controlled, open label	Experimental: 112 mL fermented yogurt with Lactobacillus delbrueckii ssp. bulgaricus OLL1073R-1 consumed daily for 16 wk	Sleep quality measured using PSQI at baseline and end point	Sleep quality improved (PSQI score decreased) in experimental vs. control
			Control: No yogurt
Takada et al., 2017 [43]	94 Japanese healthy students, aged 30 y or younger, M and F	Double-blind, placebo-controlled, parallel arm	Experimental: 100 mL fermented milk with Lactobacillus casei	Sleep quality measured using Oguri-Shirakawa-Azumi Sleep Inventory	No between-group differences in changes in total sleep score
			Control: 100 mL placebo milk matched for acidity and flavor	Multiple sleep dimensions measured using single-channel EEG	Self-reported sleepiness decreased (higher scores represent less sleepiness) and sleep time increased in experimental vs. control
			Experimental and control beverages consumed daily for 11 wk (8 wk until stressful stimulus and 3 wk after)	Measures collected at baseline, wk 6, wk 8, wk 9, and wk 11	N3 stage sleep and δ power was decreased in control vs. experimental
Markus et al., 2005 [57]	28 Dutch healthy students: (14 with sleep complaints, 14 without), mean age: 22 y (range not provided), M and F	Double-blind, placebo-controlled, randomized crossover	Experimental: Milkshake with 20 g of Trp-enriched A-LAC	Sleepiness measured using Stanford Sleepiness Scale in the evening before and morning after the meal	Trp:LNAA was higher in experimental vs. control; observed in both poor and good habitual sleepers
			Control: Energy-matched placebo milkshake with 20 g sodium caseinate	Plasma Trp:LNAA levels after the meal	Sleepiness decreased in experimental vs control; observed in both good and poor habitual sleepers
			Beverages consumed with standard meal on 1 night
Ong et al., 2017 [46]	10 Australian college students, mean age: 27 y (range not provided), M only	Double-blind, placebo-controlled, randomized crossover	Experimental: Milkshake with 20 g of Trp-enriched A-LAC	Multiple sleep dimensions measured using wrist actigraphy	Total sleep time was significantly higher in experimental vs. control
			Control: Energy-matched placebo milkshake with 20 g sodium caseinate		Sleep efficiency was significantly higher in experimental vs. control
			Beverages consumed with standard meal on 2 nights

A-LAC, α-lactalbumin; DIS, difficulty initiating sleep; DMS, difficulty maintaining sleep; EEG, electroencephalogram; F, female; GOS, galacto-oligosaccaride; LNAA, large neutral amino acid; M, male; PSQI, Pittsburgh Sleep Quality Index; REM, rapid eye movement; Trp, tryptophan; WASO, wake after sleep onset; WHIIRS, Women’s Health Initiative Insomnia Rating Scale.