Table 2.

Hair cortisol and sleep disorders in children.

Reference	Number of Children and Mean Age	Characteristics of Participants	How the Analysis of Sleep Was Performed	Mean Concentration of Hair Cortisol (HCC)	Main Findings of the Study Related to Hair Cortisol Concentration
Flom et al., 2017	Age: 12 months. Mean age: 12.18 N = 111	Healthy infants who had no known hearing, visual, neurological, or developmental disorders. Infant ethnicity: Caucasian 65.5% Asian 4.5% Black 4.5% Hispanic 1.8% Native American 0% Multiracial/Other 23.6% Infants were classified into High HCC and Low HCC Salivary Cortisol concentrations (SCC) were also measured at waking and bedtime and infants were classified to steep slope and flat slope.	The Brief Infant Sleep Questionnaire (BISQ; Sadeh, 2004) completed by mothers. Infant nighttime sleep duration: time in hours that the infant typically spends asleep between 7 p.m. and 7 a.m. Sleep disruption: number of night wakings (<2 times; >2 times per night).	HCC (pg/mg): 86.26 ± 183.63.	Infants who slept 10 h or more each night at 12 months had lower HCC than infants who slept less than 10 h. Sleep disruption was higher for infants with flat slope/high HCC compared to infants with a steep slope/high HCC. Higher infant HCC was associated with greater infant waking SCC, bedtime SCC, but not with diurnal slope. Sleep disruption was not related to infant HCC at 12 months.
Eythorsdottir et al., 2020	Age: 2–6 years. Mean age: 5.3 years. N = 68 for sleep information. N = 72 for hair cortisol measurements.	Pre-school children having factors for overweight predisposition.	Objective sleep characteristics (sleep duration, sleep latency and sleep efficiency) assessed by an ActiGraph GT3X during a continuous period of 5 days and nights.	Cortisol levels (pg/mg): 109. Cortisol levels overall median range = 7–890.	Sleep characteristics were generally not associated with log transformed cortisol levels.
Maurer et al., 2016	Healthy children born very preterm (<32nd gestational weeks): Mean age: 9.5 ± 1.4 years. Age range: 7.4–12.4 N = 85 Healthy children full term born: Mean age: 9.6 ± 1.4 years Age range: 6.9–13 N = 91	Healthy children at school age.	Sleep was assessed using in-home polysomnography (PSG) during a single night at the children’s home. Objective sleep indices were evaluated: sleep continuity, sleep efficiency and nocturnal awakening. Sleep architecture (%): Stage 1 sleep, stage 2 sleep, SWS (SWS: Stages 3 and 4 sleep), REM sleep, and REM latency (min).	Hair cortisol values (truncated to a value of 2 inter quartile above the median and adjusted for socio-demographic characteristics) Very pre-term Cortisol mean: 2.0 ± 2.1 Full-term Cortisol mean: 1.9 ± 1.8	A negative association between hair cortisone and child age; boys had significantly higher hair cortisol and cortisone levels than girls. A negative association between sleep duration and child age; boys showed longer REM sleep latency than girls. No other significant relations between sleep measures and child age.