Vitamin D Supplementation and Sleep: A Systematic Review and Meta-Analysis of Intervention Studies

Abstract

Background: Vitamin D deficiency is associated with sleep disorders and poor sleep quality. Whether vitamin D supplementation (VDS) helps resolve these problems remains unclear. Objective: To systematically review the effect of VDS on sleep quantity, quality, and disorders, and perform a meta-analysis of available data. Methods: The reporting of this review followed the PRISMA statement. VDS human interventions studies that reported on sleep quality, quantity, or disorders were included. Medline, CINAHL, EMBASE, PsycInfo, the Cochrane Library, Clinicaltrials.gov, and the ICTRP were searched, in addition to the references of the included articles and previous relevant reviews, without language or time restrictions. Included studies were critically appraised, findings were narratively synthesized, and a meta-analysis was conducted. Furthermore, the overall certainty of the evidence was assessed. Results: A total of 19 studies were included (13 randomized controlled trials (RCTs), 1 opportunistic addition to an RCT, 4 pre−post studies, and 1 pre−post study analyzed as a case series); 3 RCTs were meta-analyses. The risk of bias was generally low. Pre−post studies showed a significant improvement in sleep quality with VDS. Similarly, the results of the meta-analysis revealed a statistically significant decrease in the Pittsburgh Sleep Quality Index with VDS compared with placebo (mean difference, −2.33 (95% CI, −3.09, −1.57); p < 0.001; I2 = 0%), with a moderate certainty of evidence. The results regarding the effect of VDS on sleep-related impairment, difficulty, and disorders, as well as sleepiness and restless legs syndrome, were not unanimous. Conclusions: VDS is promising in improving sleep quality; however, its effect on sleep quantity and disorders needs to be further investigated.

Keywords: meta-analysis; sleep; systematic review; vitamin D.

Figure 1

Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) diagram of study selection. ICTRP: International Clinical Trials Registry Platform.

Figure 2

Risk of bias of included studies. (a). Risk of bias of included randomized controlled trials. (b). Risk of bias of included non-randomized studies [24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42].

Figure 2

Risk of bias of included studies. (a). Risk of bias of included randomized controlled trials. (b). Risk of bias of included non-randomized studies [24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42].

Figure 3

Meta-analysis of the effect of vitamin D supplementation on sleep quality assessed by the Pittsburg Sleep Quality Index. Mean differences for each study are represented by squares, and 95% Confidence Intervals are represented by the lines through the squares. The pooled mean differences are represented by diamonds. Between-study heterogeneity was assessed with the use of the I² statistic [25,27,30].