Although the evidence is based on randomized controlled trials and meta-analyses, the risk of bias, inconsistent results, indirectness in relation to insomnia treatment, imprecision, and potential publication bias significantly reduce the certainty. The overall evidence is limited by small sample sizes, short intervention periods, heterogeneity between studies, and a reliance on self-reported sleep measures.
| Reference | Study type | Population | Intervention and comparison | Outcomes | Risk of bias [Table «Additional comments for included studies...»2 Additional comments] |
|---|---|---|---|---|---|
| RCT=randomized controlled trial; SR=systematic review; MA=meta-analysis | |||||
| «Abboud M. Vitamin D Supplementation and Sleep: A S...»1 | SR, MA | adults Iran, USA, New Zeeland, Turkey, China, Netherlands |
interventions studies | Sleep quantity, quality (PSQI) | Moderate |
| «Chan V, Lo K. Efficacy of dietary supplements on i...»2 | SR, MA | Adults Malaysia, Iran, United Kingdom, Australia, Israel, Turkey, USA; Germany, Italy, France |
RCTs | Different sleep quality parameters | Moderate |
| «Santi D, Debbi V, Costantino F, et al. Microbiota ...»3 | SR, MA | Children, adults (probiotic only among adults) N/A |
RCTs | Different sleep quality parameters | Moderate |
| «Bulman A, D'Cunha NM, Marx W, et al. The effects o...»4 | SR, MA | All ages Japan, Asia, USA, Europe, Australia |
RCTs | Different sleep quality parameters | Low |
| Reference | Comments |
|---|---|
| «Abboud M. Vitamin D Supplementation and Sleep: A S...»1 | The nature of studies, risk of bias. |
| «Chan V, Lo K. Efficacy of dietary supplements on i...»2 | Risk of bias, partially blinding incomplete, some studies with industry funding |
| «Santi D, Debbi V, Costantino F, et al. Microbiota ...»3 | Small sample size, risk of bias. |
Results
| Reference | Number of studies and number of patients (I/C) | Absolute number of events (%) I | Absolute number of events (%) C | Relative effect (95% CI) |
|---|---|---|---|---|
| Level of evidence: low *Statistically significant The quality of evidence is downgraded due to (study limitations, inconsistency, indirectness, imprecision, publication bias). The quality of evidence in upgraded due to large or very large effects, dose-response gradient, effect of plausible residual confounding). I= intervention; C=comparison; CI=confidence interval: MD=mean difference; SMD Standard mean difference |
||||
| «Abboud M. Vitamin D Supplementation and Sleep: A S...»1 | Vitamin D supplementation 3 studies (111/112) |
N/A | N/A | MD -2.33 * (-3.09 to -1.57) moderate |
| «Chan V, Lo K. Efficacy of dietary supplements on i...»2 | Amino acid supplementation 2 studies (40/38) |
N/A | N/A | MD -1.27 * (-2.35 to -0.20 moderate |
| Melatonin supplementation 7 studies (205/199) |
N/A | N/A | MD −1.21 * (-2.17 to -0.24) low |
|
| Vitamin D 4 studies (200/202) |
N/A | N/A | MD −1.63 * (-3.15 to -0.10) low |
|
| Omega-3 2 studies (73/63) |
N/A | N/A | MD 0.13 (-0.84 to 1.09) very low |
|
| «Santi D, Debbi V, Costantino F, et al. Microbiota ...»3 | Probiotics 8 studies (274/261) |
N/A | N/A | MD -0.40 * (-0.79 to -0.02) moderate |
| «Bulman A, D'Cunha NM, Marx W, et al. The effects o...»4 | L-theanine 12 studies (454/444) |
N/A | N/A | SMD 0.44 * (0.04 to 0.84) moderate |