Do not sleep on vitamin D: vitamin D is associated with sleep variability in apparently healthy adults

Vitamin D is associated with sleep quality and duration, but it is unclear whether vitamin D status influences sleep variability. Therefore, we sought to determine whether vitamin D status was associated with sleep variability in healthy adults. We assessed objective sleep, including timing and duration standard deviation (SD) using the Philips Actiwatch Spectrum and subjective sleep quality using the Pittsburgh Sleep Quality Index (PSQI) in 130 adults. We measured plasma 25(OH)D concentration to assess vitamin D. We used one-way ANOVAs and Kruskal-Wallis tests to compare sleep in participants characterized as vitamin D deficient (<20 ng/mL), insufficient (21-29 ng/mL), and sufficient (>30ng/mL). We used covariate-adjusted linear regression to assess associations between vitamin D status and sleep metrics. We compared differences in "low" and "high" sleep variability based on vitamin D status using the Chi-squared test. There was an effect of vitamin D status on sleep timing SD (Kruskal-Wallis, P = 0.021) and sleep duration SD (Kruskal-Wallis, P < 0.001). There was an inverse association between vitamin D status with sleep duration SD (after covariate adjustment R² = 0.267, P < 0.001, deficient vs. sufficient P = 0.050, insufficient vs. sufficient P = 0.022). There was no effect of vitamin D status on objective sleep duration, efficiency, or PSQI scores (P > 0.05). We did not observe differences in "low" and "high" sleep timing SD based on vitamin D status (χ² = 5.43, P = 0.066), but we did for sleep duration SD (χ² = 22.4, P < 0.001). Our data indicate that individuals with poor vitamin D status exhibit greater objective sleep variability. Clinical Trial Registry: https://www.clinicaltrials.gov/; Unique identifiers NCT04334135, NCT04244604, and NCT04576338.NEW & NOTEWORTHY Our findings reveal that individuals with lower circulating vitamin D concentrations experience greater sleep variability compared with those with higher circulating concentrations. This supports the growing body of evidence suggesting an important link between vitamin D status and sleep health.