Table 2.

Association between sleep duration and emotional regulation in children aged 0–4 years

No of studies	Design	Quality Assessment					No of participants	Absolute effect	Quality
		Risk of bias	Inconsistency	Indirectness	Imprecision	Other
Mean age ranged between 1 month and 4.7 years. Intervention studies were between 1 day and 25 days (in-home protocol), and longitudinal studies were up to 6 years. Sleep duration was assessed by actigraphy, polysomnography or parent report. Emotional regulation was assessed through various instruments (e.g. video-recording, cortisol response, or questionnaires).
2	Randomized triala	No serious risk of bias	No serious inconsistency	No serious indirectness	No serious imprecision	None	22	Nap deprivation resulted in moderate-to-large effects on self-regulation strategies, with decreases in skepticism (d = 0.77; 7% change), negative self-appraisal (d = 0.92; 5% change) and increases in physical self-soothing (d = 0.68; 10% change), focus on the puzzle piece that would not fit (perseveration; d = 0.50; 9% change) and insistence on completing the unsolvable puzzle (d = 0.91; 10% change). After losing daytime sleep, toddlers were less able to engage effectively in a difficult task and reverted to less mature self-regulation strategies than when they were well rested [42]. When sleep restricted, children displayed less confusion in response to neutral pictures, more negativity to neutral and negative pictures, and less positivity to positive pictures. Sleep restriction also resulted in a 34% reduction in positive emotion responses (solvable puzzle), as well as a 31% increase in negative emotion responses and a 39% decrease in confused responses (unsolvable puzzle) [43].	HIGH
1	Non-randomized trialb	No serious risk of bias	No serious inconsistency	No serious indirectness	Serious imprecisionc	None	7	The cortisol awakening response was robust after nighttime sleep, diminished after sleep restriction, and smaller but distinct after morning and afternoon (not evening) naps. Cortisol remained elevated 45 min after morning and afternoon naps [44].	VERY LOW
5	Longitudinal studyd	No serious risk of bias	No serious inconsistency	No serious indirectness	No serious imprecision	None	46,959	Out of 5 longitudinal analyses, 2 reported that shorter sleep duration was associated with poorer emotional regulation at follow-up [45, 46] while 3 reported null findings [47–49].	LOW
17	Cross-sectional studye	No serious risk of bias	Serious inconsistencyf	No serious indirectness	No serious imprecision	None	16,536	Out of 17 cross-sectional analyses, 8 reported that shorter sleep duration was associated with poorer emotional regulation [50–57], 7 reported null findings [38, 49, 58–62], and 2 reported opposite associations [63, 64].	VERY LOW

Due to heterogeneity in the measurement of sleep and emotional regulation, a meta-analysis was not possible

^aIncludes 2 randomized cross-over studies [42, 43]

^bIncludes 1 non-randomized intervention [44]

^cOnly one study was published with a sample size of N = 7 so the risk of imprecision is high (the quality of evidence was downgraded from “low” to “very low”)

^dIncludes 5 longitudinal studies [45–49]

^eIncludes 17 cross-sectional studies [38, 49–64]

^fStudies reported mixed findings (the quality of evidence was downgraded from “low” to “very low”)