The Effect of Vitamin D Supplementation on Circadian Rhythms and Sleep

Vitamin D is an essential vitamin and hormone that the body either makes or obtains from food. It plays a crucial role in physiological functions, such as calcium homeostasis, bone mineralization, and immune support. Previous literature also provides indirect evidence suggesting a possible link between vitamin D and circadian rhythms. For instance, vitamin D is produced in response to the primary circadian influencer, sunlight. It is also fundamental for melatonin production, the sleep-wake hormone, and has receptors located in the ‘circadian center’ of the brain (suprachiasmatic nucleus). However, no known research has been done studying the effect of vitamin D on circadian rhythms. Thus, the aim of this study is to see if vitamin D supplementation alters circadian rhythm parameters and sleep. Participants between the ages of 18-80 were recruited to supplement with 4000 IU of vitamin D for four weeks. Data on circadian rhythms (amplitude, acrophase, mesor), objective and subjective sleep, and subjective mood were collected pre- and post-supplementation. No significant differences were observed in circadian parameters, but there were changes in sleep and mood. Specifically, overall time slept decreased from pre- (463.8 ± 102.7 min) to post- supplementation (423.0 ± 80.4 min; p=0.03), subjective sleep quality increased from pre- (5.88 ± 2.40) to post-supplementation (4.55 ± 2.30; p=0.01), and self-reported depression scores decreased from pre- (3.95 ± 3.37) to post-supplementation (2.95 ± 3.69; p=0.02). The data suggests that 4000 IU of vitamin D is not effective in improving circadian rhythms. However, four weeks of 4000IU is sufficient for altering sleep and mood. Funding provided by Alma College's CORE program. This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.