The new study finds progressively higher levels of daytime sleepiness were correlated inversely with progressively lower levels of vitamin D, especially in black people.
Led by Dr David McCarty from Louisiana State University Health Sciences Centre, USA, suggests that people with lower levels of vitamin D may be at increased risk of high levels of daytime sleepiness, and other sleep disorders.
“The results suggested the novel possibility that vitamin D deficiency-related disease has a yet-to-be-identified mechanistic role in the presentation of sleepiness, sleep disorders, or both,” said the team.
The research team said that the findings are the first to demonstrate a significant relationship between sleepiness and vitamin D.
"While we found a significant correlation between vitamin D and sleepiness, the relationship appears to be more complex than we had originally thought," said McCarty. "It's important to now do a follow-up study and look deeper into this correlation."
He added that it is logical for race to affect this relationship because increased skin pigmentation is an established risk factor for low vitamin D.
Appearing online in the Journal of Clinical Sleep Medicine, the research involved studying a consecutive series of 81 sleep clinic patients who complained of sleep problems and nonspecific pain.
All patients eventually were diagnosed with a sleep disorder, which in the majority of cases was obstructive sleep apnea, said the McCarty and his team.
Vitamin D levels were measured by blood sampling, and sleepiness was determined using the Epworth Sleepiness Scale.
The team found that in patients without vitamin D deficiency, sleepiness scores were inversely correlated with vitamin D concentration (r = 0.45, p < 0.05).
Among the patients who had vitamin D defieicy (defined as lower than 20 ng/mL of 25OHD), sleepiness was directly correlated with serum 25OHD levels in black people (r = 0.48, p < 0.05) but not white.
The study was not designed to examine causality. However, the authors' previous and current research suggests that suboptimal levels of vitamin D may cause or contribute to excessive daytime sleepiness, either directly or by means of chronic pain.
Source: Journal of Clinical Sleep Medicine
Published online ahead of print, doi: 10.5664/jcsm.2266
“Vitamin D, Race, and Excessive Daytime Sleepiness”
Authors: David E. McCarty, Aronkumar Reddy, Quinton Keigley, Paul Y. Kim, Andrew A. Marino,