However, there was high heterogeneity between some of the studies, especially those involving melatonin.
Heterogeneity could refer to differences in the study design and interventions, which could affect the analysis outcome.
Researchers at The Hong Kong Polytechnic University searched for RCTs published on databases Ovid Emcare, Ovid Medline that assessed the use of dietary supplements on sleep quality.
The 15 RCTs studied were published between 2010 and 2020.
They found that melatonin, vitamin D, and amino acids L-theanine, have shown significant benefit on subjective sleep quality – as assessed by the Pittsburgh Sleep Quality Index (PSQI).
The PSQI consists of seven components, including sleep latency, sleep duration, habitual sleep efficacy, use of medications for sleep, and daytime dysfunction as recalled by the subjects themselves.
The lower the PSQI scores, the better the sleep quality.
Five out of the seven RCTs on melatonin showed a significantly lower PSQI for the intervention group.
As for vitamin D, three out of the four RCTs studied also showed a lower PSQI for the intervention group.
The only two RCTs on amino acids supplementation showed a pooled mean difference of – 1.27 between the intervention and control group, with a 95% confidence interval.
The researchers also did a narrative review on 16 other RCTs, which studied the impact of other supplements, magnesium, zinc, resveratrol, and nitrate in improving sleep quality.
These 16 RCTs were not included in the meta-analysis as they did not have comparable studies for meta-analysis or did not provide the relevant data.
“The major strength of our meta-analysis is that it comprehensively evaluates the efficacy of dietary supplements in improving sleep quality across various populations.
“In addition, we only included RCTs for review, which provided higher quality of evidence,” the researchers said.
Heterogeneity of studies
However, the researchers cautioned that there was high heterogeneity among the RCTs involving melatonin and vitamin D.
In the case of melatonin, the I2 value – which measures the extent of heterogeneity among the RCTs – is 79%, while that of vitamin D is 85%. Both figures fall into the category of substantial heterogeneity.
However, for vitamin D, after excluding one RCT, the I2 value dropped from 85% to 0%. The I2 value for melatonin remained similar regardless of whether a particular study has been excluded.
The I2 value of the two amino acid RCTs on the other hand is 0%.
“The heterogeneity of studies using melatonin and vitamin D supplements was high, despite the use of consistent methods for subjective sleep quality measurement.
“RCT with longer duration and larger sample size should be conducted to verify our findings,” the researchers concluded.
Source: Postgraduate Medical Journal
Efficacy of dietary supplements on improving sleep quality: a systematic review and meta-analysis
Authors: Kenneth Lo, Vicky Chan