Vitamin D Supplementation and Sleep: A Systematic Review and Meta-Analysis of Intervention Studies.
Level 1 - systematic review of randomized trials
Systematic review and meta-analysis of randomized controlled trials
PubMed 35268051 · doi:10.3390/nu14051076
What was done
A systematic review and meta-analysis following PRISMA guidelines evaluating the effect of vitamin D supplementation on sleep quantity, quality, and disorders. Seven databases (Medline, CINAHL, EMBASE, PsycInfo, Cochrane Library, Clinicaltrials.gov, ICTRP) and reference lists were searched without time or language restrictions. The review included 19 human intervention studies (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). Studies were critically appraised, findings narratively synthesized, and a meta-analysis conducted with certainty of evidence assessed.
What was found
A meta-analysis of 3 RCTs showed a statistically significant reduction in Pittsburgh Sleep Quality Index (PSQI) scores with vitamin D supplementation compared to placebo (mean difference -2.33, 95% CI -3.09 to -1.57; p < 0.001; I2 = 0%), with moderate certainty of evidence. Pre-post studies also showed significant improvements in sleep quality. Findings regarding sleep-related impairment, difficulty, disorders, sleepiness, and restless legs syndrome were not unanimous.
Why it matters
Vitamin D supplementation appears to improve subjective sleep quality in intervention trials. However, evidence is inconsistent or limited regarding its benefit for specific clinical sleep disorders or objective sleep quantity.
Limits
Only 3 of the 13 RCTs provided data suitable for meta-analysis. The abstract does not report total sample size, participant demographics, baseline vitamin D status, or dosing protocols, and findings on clinical sleep disorders remain inconclusive.