A 2017 double-blind, placebo-controlled, randomized clinical trial investigated the impact of vitamin D3 supplementation on sleep quality in adults with poor sleep.1 Patients (N=89) were 20 to 50 years old and predominantly female with poor sleep quality identified by the Pittsburgh Sleep Quality Index (PSQI). The PSQI differentiates “poor” from “good” sleep quality by measuring seven areas: subjective sleep quality, sleep latency, sleep duration, habitual sleep efficiency, sleep disturbances, use of sleeping medications, and daytime dysfunction over the past month. Scores range from 0 to 21 with higher scores equating to worse sleep quality and scores of five or more indicating “poor” sleep quality. In addition to the PSQI, patients were questioned on physical activity, sun exposure, and three-day food intake. Baseline 25(OH)-vitamin D levels for the intervention and placebo groups were 25.0 and 27.6 ng/mL, respectively (P=.158). Participants were not further stratified or categorized by vitamin D status. The intervention group (N=44) received 50,000 IU of Vitamin D3 soft gelatin capsules produced by Dana Pharma Company every two weeks for a total of eight weeks. At the end of the study, vitamin D levels of the intervention and placebo groups were 37.7 and 28.0 ng/mL, respectively (P<.001). Initial mean PSQI scores were 9.45 for the intervention group compared with 10.51 for the placebo group (P=.138). After eight weeks, mean PSQI scores decreased to 6.75 in the intervention group but only to 9.73 in the placebo group (P<.001). Statistical analysis accounting for the baseline differences between the groups was not reported. The difference at eight weeks remained statistically significant even after adjusting for the following confounding variables: occupation, saturated fatty acid intake, monounsaturated fatty acid intake, and time exposed to sunlight. Notably, the final mean PSQI score in the intervention group was still within the range of poor sleep quality. Thus, the clinical significance of the difference remains unclear. Additional limitations included the short duration of treatment and use of a subjective questionnaire to evaluate sleep disorders rather than actigraphy, which is a more objective measure.
A 2016 double-blind, placebo-controlled, randomized clinical trial investigated the effects of 12 months of vitamin D3 supplementation on changes in health-related quality of life, depressive symptoms, and sleep quality.2 The study included 218 overweight (body mass index ≥25 kg/m2), postmenopausal women (ages, 50–75 years old) with vitamin D insufficiency (serum 25(OH)-vitamin D concentrations ≥10 and <32 ng/mL) and poor sleep quality (PSQI scores≥5). In addition to a lifestyle-based weight-loss program, participants were randomly assigned to 12 months of either 2,000 IU per day vitamin D3 (N=109) or daily placebo (N=109). At the end of 12 months, postmenopausal women receiving vitamin D3 did not experience any statistically significant change in sleep quality (PSQI 7.4 in placebo group vs 7.6 in the vitamin D3 group; P=.21). However, the 53 women who became vitamin D replete (≥32 ng/mL) after taking vitamin D3 for 12 months showed a worsening in total PSQI sleep quality score compared with those who did not become vitamin D replete (6.2% increase in PSQI vs 5.7% decrease in PSQI; P<.01). This difference remained significant even after adjusting for the following relevant covariates: age, race/ethnicity (non-Hispanic white, others), baseline serum 25(OH)-vitamin D levels, dietary vitamin D intake, average sun exposure, and caffeine intake. Limitations of this study included a relatively homogeneous study population (Caucasian postmenopausal women in Seattle, WA), lack of testing the independent effects of vitamin D in postmenopausal women without the weight loss intervention, and using self-reported sleep measures rather than actigraphy.
1. Majid MS, Ahmad HS, Bizhan H, Hosein HZM, Mohammad A. The effect of vitamin D supplement on the score and quality of sleep in 20-50 year-old people with sleep disorders compared with control group. Nutr Neurosci. 2018; 21(7): 511–519. [STEP 2]
2. Mason C, Tapsoba JDD, Duggan C, et al. Repletion of vitamin D associated with deterioration of sleep quality among postmenopausal women. Prev Med. 2016; 93: 166–170. [STEP 2]
It is not clear. Short-term vitamin D3 supplementation of 50,000 IU every other week over eight weeks may slightly improve subjective sleep quality measures in young adults with normal and insufficient baseline 25(OH)-vitamin D levels (SOR: C, small, low-quality randomized controlled trail [RCT]). Long-term supplementation with 2,000 IU daily of vitamin D3 over one year in vitamin D–insufficient postmenopausal women attempting weight loss has no beneficial effect on subjective sleep quality (SOR: B, RCT).