Does supplementing with calcium and/or vitamin D improve sleep quality? Original paper

In this randomized controlled trial in participants with prediabetes, supplementing with a combination of calcium and vitamin D improved sleep quality compared to a placebo.

Whether supplementing with vitamin D and/or calcium improves sleep quality (the primary outcome) in people with prediabetes.

Sleep quality was assessed using the Pittsburgh Sleep Quality Index, which comprises an overall sleep quality score, as well as 7 individual dimensions of sleep (e.g., sleep efficiency, sleep latency, sleep duration). Blood levels of calcium and vitamin D were also assessed.

Two hundred twelve (212) adults living in China (average age of 58; 67% women, 33% men) with prediabetes.

In this 24-week randomized controlled trial, the participants were assigned to supplement with vitamin D (as vitamin D3; 1,600 IU), calcium (as calcium carbonate; 500 milligrams), vitamin D + calcium, or a placebo daily.

The results were adjusted for various confounders, including the participant’s age, BMI, physical activity, dietary vitamin D and calcium intake (assessed using three 24-hour dietary recalls), and sun index (based on the participant’s average weekly sunlight exposure, including the total duration of exposure and coverage with their clothing during each exposure).

Compared to the placebo group, overall sleep quality improved in the vitamin D + calcium group.

For the secondary outcomes, compared to the placebo group, daytime dysfunction improved in the calcium group, and time to fall asleep decreased (improved) in the calcium and vitamin D + calcium groups.

Also, compared to the placebo, the vitamin D level increased in the vitamin D + calcium group (+19 ng/mL), the vitamin D group (+19 ng/mL), and the calcium (+7 ng/mL) group. None of the intervention groups differed from the placebo group with respect to changes in calcium levels.

The statistical tests used were able to determine (i) whether there was a difference between any of the groups at the end of the study (but not which groups specifically differed from one another), and (ii) whether there was a difference between the placebo group with any of the intervention groups; however, a test was not used to determine whether there were differences between the intervention groups. Also, the researchers conducted an array of analyses and did not adjust for multiple comparisons.

Finally, although it’s unclear whether the change from baseline was statistically significant, the vitamin D level in the placebo group appeared to decrease from “adequate” to “insufficient”, which may have contributed to the reported differences between groups. For these reasons, the results should be considered exploratory.