Effect of Physical Exercise on Sleep Quality and Depressive Symptoms in Adults: A Systematic Review and Meta-Analysis

Keywords

depression - major depression - exercise - physical exercise - sleep quality - sleep

Introduction

Depressive symptoms are widely recognized as one of the most pressing mental health problems. The global number of incident cases has increased by almost 50% over the past 30 years, with more than 264 million people of all ages afflicted.[1] It is estimated that in Brazil, depression affects approximately 10% of the population, with a higher prevalence among elderly males.[2] It is widely recognized that depression impacts both the quality of life and daily activities.[3] [4] Furthermore, a previous meta-analysis demonstrated that adults and the elderly with depression are more likely to experience poor sleep quality,[5] further exacerbating the health condition of these individuals.

Indeed, according to the American Academy of Sleep Medicine, poor sleep quality is associated with an increased risk of mental health issues such as depression, anxiety, and posttraumatic stress disorder (PTSD).[6] [7] For example, previous literature has found that neurotransmitter imbalances such as serotonin downregulation,[8] overactivity of hypothalamic-pituitary-adrenal (HPA) axis during sleep time that results in increased levels of stress hormones such as cortisol,[9] and high levels of cytokines (chronic inflammation)[10] closely link sleep quality and symptoms of depression.

The literature has demonstrated the potential role of physical exercise in improving both sleep quality and depressive symptoms in some clinical contexts. For example, it was observed that higher physical activity was associated with fewer sleep problems and less emotional dysregulation in patients with major depressive disorder,[11] PTSD, [12] and coronavirus disease 2019 (COVID-19).[13] It is suggested that an increase in slow-wave sleep duration[11] and in sleep efficiency,[14] as well as the potential anxiolytic and antidepressant effects of exercise[15] may be responsible for these improvements. Additionally, in the perspective of biological mechanisms, physical exercise can reduce the reactivity of the HPA axis[16] and the levels of pro-inflammatory cytokines, such as interleukin 6 (IL-6) and tumor necrosis factor alpha (TNF-α),[17] as well as increase the production of brain-derived neurotrophic factor (BDNF),[18] all of which contribute to better sleep and reduced depressive symptoms.

However, although these results are promising and provide indications of the effectiveness of physical exercise in improving sleep quality and depressive symptoms in adults, there is no standardization in the application of previously published protocols, given that there are a large number of variables to be modulated for successful intervention. For example, previous studies found improvements in sleep quality with a 6-month yoga exercise program,[19] with 12 weeks of resistance exercise,[20] [21] and with a 12-week program of pilates. Moreover, in men, greater exercise frequency was associated with less daytime disfunction and less depressive symptoms, whereas in women greater frequency was associated with improved sleep quality, less depression and anger symptoms.[22] Thus, the heterogeneity concerning the different types of exercise prevents conclusions regarding the effects of physical exercise on sleep for people with depressive symptoms.

In this sense, this systematic review will provide a global view of the studies that analyzed the effects of physical exercise on sleep quality and depressive symptoms in adults, regarding the protocols used. It will also allow for the analysis of the methodological quality of the studies, enabling a more careful review of the literature. Together, these results could help health professionals develop effective interventions to improve sleep quality and reduce depressive symptoms in this population. Thus, the aim of this study is to verify, through a systematic review and meta-analysis, the impact of physical exercise on sleep quality and depressive symptoms in adults.

Methods

This present study constitutes a systematic literature review following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA)[23] guidelines, and it has been accordingly registered in the International Prospective Register of Systematic Reviews (PROSPERO) under number CRD42023460040.

Search Strategy

The search was conducted in the PubMed, Cochrane Library, and Scopus databases using the following descriptors for physical exercise: exercise, physical exercise, resistance training, strength training, and exercise therapy. For sleep quality, we used the descriptors Insomnia, Sleep Initiation and Maintenance and Disorders, Sleep Apnea Syndromes, Sleep Quality, Sleep Disturbance, and Sleep; and, for depression, depression and major depression. The target population was defined using the descriptors Adults, Middle Age, Aging, Elderly, and Aged. Moreover, the Boolean operators AND and OR were employed to combine the search terms. The search strategy is described on [supplementary file 1].

Eligibility Criteria

We included original articles and controlled clinical trials published until June 2023 involving men and women aged 18 years or older that assessed depressive symptoms and sleep quality outcomes. These articles should provide data on the impact of physical exercise on sleep quality and depressive symptoms.

To be considered for inclusion, physical exercise should be the primary intervention of the studies. The exercise protocol should have a duration of at least 2 weeks. Additionally, the studies were required to include a pre- and postintervention assessment of sleep quality and depressive symptoms.

Exclusion criteria were also established, encompassing review articles and studies combining physical exercise with other interventions, such as medication or dietary changes.

Sleep quality could be evaluated using actigraphy, the Pittsburgh Sleep Quality Index (PSQI), full polysomnography (PSG), or the Oviedo Sleep Questionnaire. To assess depressive symptoms, the following instruments could be employed: the Center for Epidemiological Studies Depression Scale (CES-D), the Hospital Anxiety and Depression Scale-Depression subscale (HADS-D), the Beck Depression Inventory (BDI), the Taiwan Depression Questionnaire (TDQ), the Geriatric Depression Scale (GDS), the Self-Rating Depression Scale (SDS), or the Hamilton Depression Rating Scale (HDRS17).

The patient, intervention, comparison, outcome (PICO) question for the present study is: “Does physical exercise improve sleep quality and depressive symptoms in adults?”

Review and Data Extraction Procedures

The study's primary outcomes were sleep quality, while depressive symptoms were considered secondary outcomes. Differences in post- to preintervention sleep quality and depressive symptoms were extracted from each study. The data review and collection process were conducted systematically to ensure accuracy and consistency, being performed by two independent reviewers.

The first stage involved database searches. The second stage entailed the screening of article titles and abstracts. Subsequently, the selected articles were read in full. During this phase, the following data were extracted from each publication: sample characteristics, exercise protocol, sleep evaluation protocol, findings related to sleep quality, as well as depression symptom assessment protocol and findings.

The results of each stage were compared, and, in the event of discrepancies, a third researcher was consulted for final analysis. The data were expressed as the mean difference and standard deviation (SD). The main author was contacted in absence of data. When the mean difference was not provided, subtraction between the post- and prevalues was performed, and SD was imputed using the following formula:

Risk of Bias Assessment

The risk of bias for each clinical trial was rated in seven domains according to the Cochrane collaboration's tool.[24] Studies with higher scores were indicative of high quality and, consequently, a low risk of bias. The Review Manager (RevMan) software (The Cochrane Collaboration, London, United Kingdom), version 5.4, was used to classify whether domains exhibited high or low risk of bias, and if domains were not clear it was classified as unclear.

Analysis of Study Quality

In addition to these aspects, a study quality assessment was also conducted using the Tool for the Assessment of Study Quality and Reporting in Exercise (TESTEX).[25] This scale assesses the methodological quality of the study based on 12 items: 1) specified eligibility criteria; 2) specified randomization; 3) allocation concealment; 4) similar baseline characteristics between groups; 5) assessor blinding for at least one key outcome: 6) outcome measured in 85% of the participants; 7) intention-to-treat analysis; 8) reported statistical group comparisons; 9) point estimates and variability measures for all reported outcome measures; 10) activity monitoring in control groups; 11) relative intensity remaining constant; and 12) exercise volume and energy expenditure. The scores of each item go up to 1 point, except for items 6 and 8, whose scores go up to 3 and 2 points, respectively. Therefore, the total score ranges from 0 to 15.

Data Analysis and Synthesis of Results

The primary outcomes are expressed as mean ± SD values. The quantitative synthesis was performed by comparing the unstandardized mean difference (USMD) of sleep quality and depressive symptoms between pre- and postintervention for both the exercise and control groups and graphically represented using forest plots. Heterogeneity among studies was evaluated using the I² index. A random effects model was used due to heterogeneity in variables among the studies. As aforementioned, the analyses were performed using the RevMan software, version 5.4. Values of p < 0.05 were considered statistically significant.

Results

[Figure 1] presents the flowchart of the included studies. Initially, a total of 931 articles were identified, comprising 286 articles from PubMed, 629 articles from the Cochrane Library, and 16 articles from Scopus. Among these, 121 articles were excluded for not meeting the inclusion criteria of being a randomized clinical trial, and another 810 articles due to their lack of relevance to the subject. Following a thorough review, three more articles were excluded: two for their failure to provide post-sleep quality data, and one for using sleep-inducing medications. Thus, 15 articles met the eligibility criteria and were included in the study. For quantitative analysis, 14 studies were chosen for their examination of overall sleep quality.

Fig. 1. Flowchart of study selection.

The characteristics of the study population are presented in [Table 1]. The publication years ranged from 2009 to 2022, encompassing adults of both genders, including elderly individuals,[19] [26] [27] elderly individuals with insomnia,[28] [29] elderly individuals with limited mobility,[30] adults with depression,[31] adults with PTSD,[20] [21] individuals with primary insomnia,[32] menopausal women,[33] postmenopausal women,[34] individuals with chronic fatigue syndrome,[35] adults and elderly individuals with mild cognitive impairment,[36] or methamphetamine-dependent individuals,[37] totaling 940 participants.

Table 1 Characteristics of the included studies

Author, year	Project	Participants
		Population	Sample size	Mean age (years)	Evaluation tools
Chen et al.,[19] 2009	RCT	Elderly	128 (IG: 62; CG: 66)	IG: 65.77 ± 4.32 CG: 72.42 ± 6.04	Sleep: PSQI Depression: TDQ
Reid et al.,[28] 2010	RCT	Insomnia	17 (IG: 10; CG: 7)	IG: 62 ± 4.5 GC: 63.5 ± 4.3	Sleep: PSQI Depression: CES-D
Chen et al.,[30] 2015	RCT	Elderly	114 (IG: 59; CG: 55)	79.15 ± 7.03	Sleep: PSQI Depression: TDQ
Choi et al.,[26] 2017	RCT	Elderly	63 (IG: 33; CG: 30)	IG: 76.6 ± 5.69 CG: 78.8 ± 5.83	Sleep: PSQI Depression: GDS
Cheung and Lee,[31] 2018	RCT	Depression	34 (IG: 17; CG: 17)	IG: 47.4 ± 11.2 CG: 48.1 ± 10.8	Sleep: PSQI Depression: HADS
Laredo et al.,[27] 2018	RCT	Elderly	38 (IG: 20; CG: 18)	IG: 75.44 ± 5.31 CG: 76.35 ± 6.45	Sleep: OSQ Depression: GDS
Aibar et al.,[34] 2019	RCT	Postmenopausal women	110 (IG: 55; CG: 55)	IG: 69.98 ± 7.83 CG: 66.79 ± 10.14	Sleep: PSQI Depression: HADS
Whitworth et al.,[20] 2019a	RCT	Adults with PTSD	30 (IG: 15; CG: 15)	IG: 27.67 ± 5.95 CG: 30.53 ± 8.66	Sleep: PSQI Depression: CES-D
Whitworth et al.,[21] 2019b	RCT	Adults with PTSD	22 (IG: 11; CG: 11)	IG: 33.8 ± 11.1 CG: 32.1 ± 15.6	Sleep: PSQI Depression: CES-D
El-Kader et al.,[32] 2020	RCT	Primary insomnia	80 (IG: 40; CG: 40)	IG: 51.27 ± 5.32 CG: 52.64 ± 4.81	Sleep: PSG Depression: BDI
Lu et al.,[33] 2020	RCT	Menopausal women	106 (IG: 52; CG: 54)	IG: 50.56 ± 3.27 CG: 50.74 ± 2.95	Sleep: PSQI Depression: SDS
Chin et al.,[29] 2022	ERC	Insomnia	27 (MIG: 9; VIG: 9; CG: 9)	MIG: 63.7 ± 4.7 VIG: 61.7 ± 2.7 CG: 63.8 ± 6.0	Sleep: PSQI Depression: HADS
Xie et al.,[57] 2022	RCT	CFS	89 (IG: 45; CG: 44)	IG: 37.943 ± 11.344 CG: 37.343 ± 9.864	Sleep: PSQI Depression: HADS
Xu et al.,[37] 2022	RCT	Methamphetamine-dependent individuals	60 (IG: 30; CG: 30)	IG: 31.30 ± 3.86 CG: 29.50 ± 4.59	Sleep: PSQI Depression: SDS
Yu et al.,[36] 2022	RCT	Adults and elderly with cognitive impairment	22 (MIG: 7; VIG: 8; CG: 7)	MIG: 60.6 ± 3.1 VIG: 59.6 ± 4.6 CG: 60.5 ± 7.3	Sleep: PSQI Depression: HADS

Abbreviations: BDI, Beck Depression Inventory; CES-D, Center for Epidemiologic Studies Depression Scale; CFS, chronic fatigue syndrome; CG, control group; GDS, Geriatric Depression Scale; HADS, Hospital Anxiety and Depression Scale; IG, intervention group; MIG, moderate intensity intervention group; OSQ, Oviedo Sleep Questionnaire; PSG, polysomnography; PSQI, Pittsburgh Sleep Quality Index; PTSD, posttraumatic stress disorder; RCT, randomized controlled trial; SDS, Self-Rating Depression Scale; TDQ, Taiwan Depression Questionnaire; VIG, vigorous intensity intervention group.

The sleep quality was assessed using the PSQI,[19] [20] [21] [26] [28] [29] [30] [31] [33] [34] [35] [36] [37] full PSG,[32] or the Oviedo Sleep Questionnaire.[27]

Depressive symptoms were assessed using the CES-D,[20] [21] [28] the HADS-D,[29] [31] [34] [35] [36] the BDI,[29] the TDQ,[19] [30] the GDS,[26] [27] or the SDS.[33] [37]

[Table 2] presents the characteristics of exercise protocols employed in the studies. Among the interventions utilized, aerobic exercise emerged as the most prevalent included in 6 out of the 15 selected studies.[28] [29] [31] [32] [36] [37] Resistance training,[20] [21] functional training,[27] exercises with elastic bands,[30] seated adapted yoga,[26] yoga,[19] [33] Qigong,[35] and Pilates[34] were also included in the physical exercise regimes.

Table 2 Characteristics of exercise protocols in the included studies

Author, year	Intervention
	Exercise protocols	Frequency	Intensity	Duration	Dropouts	Control
Chen et al.,[19] 2009	Yoga	3 times/week	NR	6 months	9	No wxercises
Reid et al.,[28] 2010	Aerobic: Week 1–6: 10–40 minutes Week 7–16: 20 or 40 minutes	Week 1–6: 4 times/week Week 7–16: 2–1 time/week	55–75% of HRmax	4 months	5	Sleep hygiene
Chen et al.,[30] 2015	Resistance band: 40 minutes	3 times/week	NR	6 months	12	No exercises
Choi et al.,[26] 2017	Yoga: 30–40 minutes	4 times/week	8–14 of RPE scale	12 weeks	9	No exercise
Cheung and Lee,[31] 2018	Supervised aerobic: 60 minutes Aerobic Unsupervised aerobic: 30 minutes	1 time/week 2 times/week	60% of HRmax	12 weeks	2	No exercise
Laredo et al.,[27] 2018	Functional training: 60 minutes	3 times/week	Self-determined	10 weeks	4	No exercises
Aibar et al.,[34] 2019	Pilates: 60 minutes	2 times/week	NR	12 weeks	3	Exercises guidance
Whitworth et al.,[20] 2019a	Resistance training: 30 minutes	3 times/week	8RM	3 weeks	3	Attention session
Whitworth et al.,[21] 2019b	Resistance training: 30 minutes	3 times/week	8RM	3 weeks	5	Attention session
El-Kader et al.,[32] 2020	Aerobic: 45 minutes	3 times/week	60–70% of HRmax	6 months	22	No exercise
Lu et al.,[33] 2020	Yoga: 60 minutes	3 times/week	NR	24 weeks	0	Household tasks
Chin et al.,[29] 2022	Moderate walk: 50 minutes Vigorous walk: 25 minutes	3 times/week	MIG: 3.25 METs VIG: 6.5 METs	3 months	29	Stretching
Xie et al.,[57] 2022	Qigong: 60 minutes Remote: 30 minutes	1 time/week 6 times/week	NR	12 weeks	0	CBT
Xu et al.,[37] 2022	Aerobic: 60 minutes	5 times/week	70–75% of HRmax	3 months	0	Rehabilitation
Yu et al.,[36] 2022	Aerobic: MIG: 50 minutes VIG: 25 minutes	3 times/week	MIG: 3.5 METs VIG: 7 METs	12 weeks	5	Lifestyle guidance

Abbreviations: CBT, cognitive-behavior therapy; HR_max, maximum heart rate; MIG, moderate intensity intervention group; NR, Not Report; PRT, progressive resistance training; RM, repetition maximum; RPE, rated of perceived exertion; VIG, vigorous intensity intervention group.

[Table 3] presents the sleep quality and depressive symptoms results from the 15 included studies. Out of the 15 studies included, 12 observed an improvement in sleep quality.[19] [20] [21] [28] [29] [31] [32] [33] [34] [37] [38] [39] This improvement was substantiated by a reduction ranging from 0.53 to 4.2 in the PSQI score. Studies reporting statistically significant changes had exercise programs with a duration ranging from 3 to 26 weeks and a minimum frequency of twice per week.[19] [20] [21] [26] [28] [29] [31] [32] [33] [34] [37] [39] Furthermore, the study that employed full PSG demonstrated an approximately 11% improvement in sleep efficiency and an approximate reduction of 15 minutes in wake after sleep onset.[32] Moreover, the metanalysis found that physical exercise improved sleep quality (USMD: −1.19; 95% confidence interval [95%CI]: −1.66 to −0.73; I² = 42%), as shown in [Fig. 2].

Table 3 Summary of Sleep Quality and Depression Pre- and Post-Intervention

Authors/Year	Sleep quality, score		Depressive symptoms, score
	Pre:	Post:	Pre:	Post:
Chen et al. 2009	IG: 1.18 ± 3.16 CG: 1.05 ± 0.75	IG: 0.65 ± 0.68 CG: 1.23 ± 0.76	IG: 6.58 ± 7.57 CG: 5.02 ± 5.52	IG: 3.27 ± 6.78 CG: 7.85 ± 8.31
Reid et al. 2010	IG: 1.90 ± 0.57 CG: 1.71 ± 0.49	IG: 0.08 ± 0.63 CG: 1.14 ± 0.69	IG: 9.36 ± 8.63 GC: 8.84 ± 6.31	IG: 2.52 ± 2.15 CG: 9.47 ± 8.2
Chen et al. 2015	IG: 8.14 ± 3.84 CG: 6.47 ± 4.71	IG: 7.68 ± 4.24 CG: 7.64 ± 4.91	IG: 7.63 ± 8.4 CG: 7.95 ± 9.07	IG: 5.44 ± 7.8 CG: 11.53 ± 9.85
Choi et al. 2017	IG: 6.12 ± 2.72 CG: 5.83 ± 2.64	IG: 4.97 ± 2.27 CG: 5.97 ± 2.71	IG: 5.88 ± 2.97 CG: 4.57 ± 3.33	IG: 3.82 ± 2.82 CG: 4.63 ± 3.14
Cheung et al. 2018	IG: 12.0 (5.5-15.0) CG: 13.0 (9.5-16.0)	IG: 9.0 (6.0-13.0) CG: 13.0 (8.5-16.5)	IG: 9.1 ± 3.6 CG: 11.1 ± 3.0	IG: 7.3 ± 3.5 CG: 10.1 ± 4.7
Laredo et al. 2018	IG: 29.30 ± 16.37 CG: 36.11 ± 6.37	IG: 22.25 ± 13.86 CG: 38.78 ± 7.35	IG: 4.83 ± 2.72 CG: 4.28 ± 2.76	IG: 1.92 ± 1.24 CG: 6.11 ± 4.42
Aibar et al. 2019	IG: 8.56 ± 4.98 CG: 7.10 ± 4.42	IG: 7.16 ± 4.9 CG: 8.38 ± 4.28	IG: 5.33 ± 3.85 CG: 5.25 ± 3.54	IG: 3.98 ± 2.93 CG: 6.81 ± 3.6
Whitworth et al. 2019a	IG: 10.42 ± 3.32 CG: 10.83 ± 5.08	IG: 7 ± 3.16 CG: 10 ± 5.34	IG: 14 ± 7.03 CG: 13.42 ± 6.1	IG: 11.63 ± 7.15 CG: 13.83 ± 5.08
Whitworth et al. 2019b	IG: 11.3 ± 4.9 CG: 7.8 ± 2.5	IG: 7.1 ± 4.1 CG: 8.4 ± 2.9	IG: 15.1 ± 6.8 CG: 13.2 ± 3.9	IG: 11.0 ± 7.0 CG: 13.6 ± 8.0
El-Kader et al. 2020	IG: 69.53 ± 7.14 CG: 70.14 ± 6.93	IG: 80.61 ± 9.38 CG: 68.75 ± 7.13	IG: 7.68 ± 1.54 CG: 7.35 ± 1.82	IG: 5.17 ± 1.22 CG: 8.22 ± 1.93
Lu et al. 2020	IG: 7.63 ± 1.52 CG: 7.52 ± 1.41	IG: 6.01 ± 1.44 CG: 7.47 ± 1.37	IG: 36.62 ± 2.37 CG: 37.04 ± 2.44	IG: 30.22 ± 2.11 CG: 36.33 ± 2.54
Chin et al. 2022	MIG: 9.9 ± 3.10 VIG: 11.8 ± 1.9 CG: 11.12 ± 3.3	MIG: 6.6 ± 2.69 VIG: 7.3 ± 3.53 CG: 10 ± 4.46	MIG: 9.63 ± 1.85 VIG: 10.3 ± 2.36 CG: 11.17 ± 3.07	MIG: 3.00 ± 3.27 VIG: 3.31 ± 1.97 CG: 7.42 ± 5.32
Xie et al. 2022	IG: 6.756 ± 3.523 CG: 7.705 ± 2.953	IG: 4.200 ± 2.085 CG: 5.295 ± 2.378	IG: 6.844 ± 4.033 CG: 6.705 ± 3.927	IG: 3.444 ± 2.563 CG: 4.705 ± 3.069
Xu et al. 2022	IG: 6.83 ± 2.36 CG: 6.27 ± 2.08	IG: 4.57 ± 1.38 CG: 6.83 ± 1.53	IG: 53.20 ± 5.12 CG: 54.80 ± 8.95	IG: 39.37 ± 6.09 CG: 54.07 ± 6.12
Yu et al. 2022	MIG: 9.7 ± 4.3 VIG: 13.1 ± 3.5 CG: 11 ± 3.5	MIG: 7.7 ± 3.4 MIG: 9.3 ± 3.9 CG: 11.6 ± 4.2	MIG: 10.9 ± 1.9 VIG: 7.5 ± 4.7 CG:6.9 ± 3.5	MIG: 8.9 ± 2.3 VIG: 5.6 ± 4.2 CG: 6.4 ± 6.2

Notes: MI – Moderate intensity; VIG – Vigorous Intensity Intervention Group; IG – Intervention group; CG – Control group.

Fig. 2. Forest plot for the exercise effect on sleep quality. The square represents the meaning difference between exercise and control groups. The line represents the 95% confidence interval (95%CI). The diamond reflects the pooled effects of exercise. Abbreviation: IV, inverse variance and random effects.

Out of the 15 included studies, 12 observed a significant improvement in depressive symptoms.[19] [26] [27] [28] [29] [30] [32] [33] [34] [36] [37] [39] In addition, the metanalysis found a significant reduction in depressive symptoms following physical exercise (USMD: −3.51; 95%CI: −4.66 to −2.36; I² = 57%), as shown in [Fig. 3].

Fig. 3. Forest plot for the exercise effect on depressive symptoms. The square represents the meaning difference between exercise and control groups. The line represents the 95% confidence interval (95%CI). The diamond reflects the pooled effects of exercise. Abbreviation: IV, inverse variance and random effects.

[Table 4] presents the studies quality assessment. According to the TESTEX scale (0–15 points), 7 out of the 15 included studies did not score above 10 points. The weakest aspects in these studies were: intention-to-treat analysis (27%), control group monitoring (20%), and relative intensity (13%).

Table 4 Assessment of Sleep Quality according to the TESTEX Scale

Author, year	Eligibility	Randomization	Allocation	Similar groups	Blinding of assessors	Results assessed in 85% of the participants	Intention-to-treat	Between-groups comparison	Point measures	Control group monitoring	Relative intensity	Exercise volume and energy	Total score
Chen et al.,[19] 2009	1	1	1	1	0	3	1	2	1	0	0	0	10
Reid et al.,[28] 2010	1	0	0	1	0	0	0	2	1	0	0	1	6
Chen et al.,[30] 2015	1	1	1	0	0	3	0	2	1	0	0	1	10
Choi et al.,[26] 2017	1	1	0	1	0	2	0	2	1	0	0	1	9
Cheung and Lee,[31] 2018	1	1	0	1	1	2	1	2	1	0	0	1	11
Laredo et al.,[27] 2018	1	0	0	1	0	2	0	1	1	0	0	1	8
Aibar et al.,[34] 2019	1	0	0	1	1	2	0	2	1	0	0	1	9
Whitworth et al.,[20] 2019a	1	1	0	1	0	3	0	2	1	0	1	1	11
Whitworth et al,.[21] 2019b	1	1	1	1	0	3	0	2	1	1	1	1	13
El-Kader et al.,[32] 2020	1	0	0	1	0	2	0	2	1	0	0	1	8
Lu et al.,[33] 2020	1	0	0	1	0	1	0	2	1	0	0	1	7
Xie et al.,[57] 2021	1	1	1	1	0	1	1	2	1	0	0	1	10
Yu et al.,[36] 2022	1	1	1	1	1	2	0	2	1	0	0	1	11
Xu et al.,[37] 2022	1	1	1	1	1	1	0	1	1	0	0	1	9
Chin et al.,[29] 2022	1	1	1	1	1	3	0	2	1	1	0	1	13

Abbreviation: Testex, Tool for the Assessment of Study Quality and Reporting in Exercise.

Discussion

The main findings of the present study demonstrate that physical exercise can improve both sleep quality and depressive symptoms in adults and the elderly. These findings suggest the therapeutic potential of physical exercise as an alternative approach in the treatment of these conditions, with low cost and without the need for medication.[40] Among the interventions used, aerobic exercise was the most common and effective for both outcomes. It was observed that a 10 to 60-minute walk, 3 to 5 times a week with moderate to vigorous intensity, lasting between 6 and 26 weeks, significantly improved sleep quality[28] [29] [31] [32] [37] and attenuated depressive symptoms.[28] [29] [32] [37]

The duration of the training programs in our study programs ranged from 3 weeks[20] [21] to 6 months.[19] [30] [32] [33] Despite this, the heterogeneity was considered moderate, and the quality of the studies ranged from moderate to high. The source of heterogeneity came primarily from the different tools of assessing depressive symptoms and sleep quality.

For example, the depressive symptoms were assessed by TDQ,[19] [30] CES-D,[20] [21] [28] GDS,[26] [27] HADS,[29] [31] [34] [35] [36] BDI,[29] and SDS.[33] [37] Although these questionnaires differ in classification and normative table, they share the characteristic of higher scores indicating a greater tendency for individuals to exhibit depression.

In addition, regarding the evaluation of sleep quality, different methods were adopted with studies evaluating sleep quality through PSQI or Oviedo Sleep Questionnaire, or PSG. Thus, considering that questionnaires express a self-perception of the sleep quality, and the PSG's objective assessment (sleep efficiency, wake after sleep onset etc.), the results should be interpreted with caution. Despite that, the questionnaires follow a similar scoring logic: the lower the score obtained, the better the individual's classification regarding sleep quality.

Finally, the variability in interventions (that is, duration, intensity, and type of exercise) must be considered. Thus, future studies should standardize the exercise protocols to verify its effects sleep and depressive symptoms.

Regarding resistance exercise, positive outcomes were observed in the improvement of sleep quality, as well as in the reduction of depressive symptoms. Nevertheless, a prior study[20] failed to detect a significant effect of resistance exercise intervention on depression indices. Conversely, it is noteworthy to mention that other studies[41] [42] suggest that moderate to high-intensity resistance exercise is effective for treating depressive symptoms among the elderly.[42] Thus, although we cannot state, it is reasonable to speculate that higher intensities of strength exercises demonstrate a favorable effect in reducing depressive symptom in adults and the elderly.[29] [41]

The frequency and intensity of exercise are directly associated with improvements in sleep-related aspects and mental health.[29] [41] [42] Aligned with our findings, previous studies have indicated that programs of physical exercise performed 3 times a week or more,[19] [30] with moderate to vigorous intensity,[32] had a positive impact on depressive symptoms. Conversely, interventions with a frequency of less than 3 days per week tend to yield effects of lesser magnitude.[29] [37] [42]

Regarding the underlying mechanisms, exercise intensity appears to modulate the inflammatory factors with higher intensities increasing IL-6[43] and BDNF levels.[44] Additionally, when comparing the effects of a single session per week with several sessions, a decrease in TNF-α levels was found with no changes in IL-6 and BNDF, suggesting that more research is needed to fully understand the impact of the different exercise frequencies. Regarding the exercise intensity and frequency and factors such as medications and comorbidities, the present study agrees with previous literature,[45] suggesting that supervised and group exercise with moderate intensity of at least 3 times per week, may offer a treatment option for individuals who refuse or cannot tolerate medication, and may develop associated comorbidities as consequence.

Physical exercise has been found to be effective in reducing issues such as insomnia, and enhancing sleep quality, efficiency, latency, and duration. Furthermore, this nonpharmacological approach has been shown to improve sleep architecture,[46] particularly in terms of increasing deep phase sleep time (N2 and N3) in the non-rapid eye movement (NREM) phase.[47] Most human sleep occurs in the N2 phase, which is associated with bodily maintenance,[48] while N3, also referred to as deep sleep, demonstrates the highest potential for arousal and intense brain synchronization, encompassing the processing of information from the previous day's experiences.[49]

Additionally, along with the enhancement of physical exercise on sleep quality, our study also revealed an improvement in depression scores attributable to exercise, which was observed in 75% of the selected studies. In a clinical point of view, it is important to mention that this disease imposes a significant economic burden on the global healthcare system, with an estimated cost of 1.15 trillion dollars, which could triple by 2030.[50]

The literature shows that the mechanisms behind the improvement of symptoms with the antidepressant effect of structured and planned physical activity may be attributed to the regulation of physiological factors. This includes the reduction of inflammatory compounds found in depression pathology, and the promotion of brain neuroplasticity.[51] Although there is no certainty, we can speculate on some underlying mechanisms that support the premise that physical exercise exerts an antidepressant effect. For example, exercises increase the availability of tryptophan, an amido acid that is precursor to serotonin, leading to higher serotonin production in the brain;[52] [53] it also stimulates the release of dopamine by increasing the activity of the brain's reward system[54] [55] and increases the peripheral levels of BDNF.[56]

Additionally, physical exercise also has an important relation with the endocrine system, involving the release of hormones such as testosterone, endorphins, growth hormone (GH), and insulin.[57] For example, resistance training stimulates the hypothalamic-pituitary-gonadal (HPG) axis, leading to increased secretion of luteinizing hormone (LH) and stimulating the production of testosterone,[58] and the release of GH from the pituitary gland. On the other hand, aerobic exercise triggers the release of endorphins from the pituitary gland and the hypothalamus, binding to opioid receptors in the brain and inducing feelings of euphoria.[59] Thus, regarding the sleep, improved levels of testosterone, endorphin, and GH are crucial to a restorative sleep, particularly during the slow wave sleep. Furthermore, regarding the depressive symptoms, higher levels of endorphins and testosterone are linked to improved mood and reduced symptoms of depression.[59]

The present study has some limitations. The conclusions should be interpreted with caution, given that the results presented substantial heterogeneity, as these were small sample studies that showed methodological differences in assessing sleep quality and depressive symptoms. Moreover, the search terms used may not have been targeted enough to identify studies specifically examining sleep in people with depressive symptoms. This limitation should be considered in future revisions. However, our meta-analysis had some strengths. First, regardless of duration and exercise mode, significant effects were found for all variables. Second, only interventions with exercise were included in the treatment condition.

Conclusion

In conclusion, physical exercise is effective in demonstrating significant improvements in sleep quality and depressive symptoms for adults and the elderly. Intervention protocols last 12 weeks, with a minimum frequency of 3 times a week, and moderate to vigorous intensity exercise training programs, are suggested to be the most impactful.

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