Among patients with vitamin D deficiency, sleepiness and vitamin D levels were associated only among black patients. Surprisingly, this correlation was observed in a direct relationship, with higher vitamin D levels associated with a higher level of sleepiness among black patients.
"While we found a significant correlation between vitamin D and sleepiness, the relationship appears to be more complex than we had originally thought," David McCarty, principal investigator of the study, said.
"It's important to now do a follow-up study and look deeper into this correlation," he said.
According to the authors, this is the first study to demonstrate a significant relationship between sleepiness and vitamin D. They noted that it is logical for race to affect this relationship because increased skin pigmentation is an established risk factor for low vitamin D.