A new study has for the first time linked vitamin D levels to daytime sleepiness.
However, the study also reveals that race plays a significant role. Researchers found that among patients with vitamin D deficiency, sleepiness and vitamin D levels were associated only among black patients.
The findings, published in the Dec. 15 issue of the Journal of Clinical Sleep Medicine, reveal that progressively higher levels of daytime sleepiness were inversely correlated with progressively lower levels of vitamin D in patients with normal vitamin D levels.
However, researchers were surprised to discover that this correlation was observed as direct relationship in black patients with higher vitamin D levels associated with a higher level of sleepiness.
"While we found a significant correlation between vitamin D and sleepiness, the relationship appears to be more complex than we had originally thought," the study's principal investigator Dr. David McCarty, said in a statement. "It's important to now do a follow-up study and look deeper into this correlation."
The study involved a consecutive series of 81 sleep clinic patients. The patients had complained of sleep problems and nonspecific pain. All the patients in the study were eventually diagnosed with a sleep disorder, which in the majority of cases was obstructive sleep apnea.
Researchers said that this research is the first to show a significant relationship between sleepiness and vitamin D.
They also explained that the findings were logical for race to affect this relationship because increased skin pigmentation is an established risk factor for low vitamin D.
While the study was not designed to find a cause and effect, researchers said that past and current research suggests that suboptimal levels of vitamin D may cause or be partly responsible for excessive daytime sleepiness, either directly or by inducing chronic pain.