Table 3.

Main strengths and limitations of the studies included in the scoping review.

Reference	Strengths	Limitations
El-Sheik et al., 2007 [46]	Homogeneous sample: healthy children (age = 8–9, similar gender proportion) Sample size: N = 64 Sample collected at two different times (3 p.m. and 5 p.m.) Combines objective and subjective sleep assessment methods: one-week actigraphy + School Sleep habits Survey (children) and Children’s Sleep Habits Questionnaire (CSHQ) (parents)	Only IL-6 was studied
Reinhardt et. al., 2012 [51]	Homogeneous sample: healthy men Daytime workers and overnight workers were compared. Sample collected at two different times: wake time and midnight. Objective and subjective methods combined: Diaries + actigraphy Includes the study of melatonin in saliva	Small sample: N = 5 No analysis with the secondary variables assessed (depression, anxiety)
Akpinar et al., 2012 [40]	Narrow age range (control: 44.7 ± 13.75; experimental: 43.79 ± 12.72) Sample size N = 56 Healthy people and people with OSA are studied Objective and subjective methods combined: Polysomnography and Epworth Sleepiness Scale (ESS) Mieloperoxidase (MPO) was measured on blood and salivaIMC was measured as a secondary variable	Only MPO and PCR levels were assessed (other inflammatory markers such cytokines were not assessed).
Nizam et al., 2014 [41]	Polysomnography is applied to all participants (N = 52) Healthy people and people with OSA are studied Several cytokines were measured: IL-6, IL-33, IL-1β, IL-21, and pentraxin-3 (PTX3)	Unbalanced sample: 32 men and 20 women Wide age range: 21–64 years Only one sample collected
Faraut et al., 2015 [50]	Homogeneous sample: healthy men (age = 25–32) Polysomnography Sample collected at several time points (every two hours)	Small sample: N = 11 Only IL-6 was assessed
Pinto et al., 2016 [45]	Sample collected at several times (every four hours) Includes the study of melatonin in saliva	Heterogeneous sample: healthy people and people with chronic renal failure. Wide age range: 29–79 years (N = 39) Only TNFα and IL-6 were assessed Samples were collected along a period of only 24 h. Cytokines were assessed only in blood (not in saliva) Sleep assessed with only one questionary: Sleep Quality e Index Pittsburgh (PSQI)
Thimgam et al., 2015 [42]	Objective and subjective methods combined: Polysomnography and Epworth Sleepiness Scale (ESS) A polysomnogram was produced for all patients (N = 40) IMC was measured as a secondary variable	Heterogeneous sample: healthy people (5 men/3 women), OSA patients (11 men/3 women), and patients with suspected OSA (6 men/12 women) Inflammatory transcriptions were assessed, but not cytokines
Reinhardt et al., 2016 [38]	Homogeneous sample: healthy men workers with day work shift. Narrow age range (32.14 ± 7.61) Objective and subjective methods combined: Actigraphy and diaries Sample collected at three different times (wake, 2pm and bedtime)	Small sample: N = 21 Only IL-6 was studied
Yennurajalingam et al., 2017 [43]	Sample (N = 52) collected at two different times (wake and bedtime) IL-1β and IL-6 were assessed Secondary variables were measured: anxiety, depression with HADS (Edmonton Symptom Assessment Scale), pain with BPI (Brief Pain Inventory) and drugs used.	Heterogeneous sample: advanced cancer patients with at least one symptom of depression, anxiety, sleep disorders, and pain. Unbalanced sample: 32 men and 20 women Sleep assessed with only one questionary: Pittsburgh Sleep Quality Index (PSQI) Sample collected only once a week
Reinhardt et al. 2019 [48]	Homogeneous sample: healthy men workers. Narrow age range: day workers 32.14 ± 7.61 years old and night workers 32.59 ± 5.62 years old Different work shifts were analyzed Actigraphy used for 10 days (24 h/day) Sample collected at two different times TNFα, interleukin-1β (IL-1β), and IL-6 were studied Melatonin levels in saliva were assessed.	Sample size: N = 38 Different number of workers in each group (day: 21; night: 17) No secondary variable was studied
Boström et al., 2019 [44]	All participants were women. All samples collected at the same time Secondary variables were studied: functional capacity with MIDAS (Migraine Disability Assessment), depressive symptoms with BDI (Beck Depression Inventory) and quality of life (EuroQuol EQ-5D-5L)	Heterogeneous simple (N = 24): healthy women and women with migraine Wide age range: 34–65 years Sleep assessed with only one questionary: Pittsburgh Sleep Quality Index (PSQI) Samples were collected only twice along the whole research (at the beginning and at the end, after 10 weeks with nVNS). Only IL-1β was studied
Zhang et al., 2020 [49]	Homogeneous sample: nurse women that work in rotative work shifts. Daily samples collected Different cytokines, e.g., IL-6, IL-1β, and TNFα were studied. Melatonin levels in saliva were assessed. Secondary variables related to sleep were studied: insomnia, anxiety, depression (with HADS) and alert level (with PVT, psychomotor vigilance task)	Sample size: N = 32 Different sample size for the control (13) and experimental groups (19) Sleep assessed with only subjective methods: Pittsburgh Sleep Quality Index (PSQI) and Insomnia Severity Index (ISI) Samples were collected only once a week
LaVoy et al., 2020 [47]	Similar gender proportion (53% women) Narrow age range: 8–16 years Objective and subjective methods combined: Actigraphy, sleep diaries and the School Sleep Habits Survey (SSHS) Daily simple collection (at wake time) All samples were analyzed twice IL-6 and IL-1β were studied Secondary variables were studied: the z-score of body mass index (zBMI), collection time, and season of data collection.	Heterogeneous sample: healthy people and people with at least a diagnostic of attention deficit hyperactivity disorder (n = 1), generalized anxiety disorder (n = 5), major depressive disorder (n = 2), social anxiety disorder (n = 4), specific phobia (n = 3), pervasive developmental disorder (n = 1), depressive disorder not otherwise specified (n = 1), and disruptive mood dysregulation disorder (n = 1).