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A new study suggests a significant link between excessive daytime sleepiness and deficiency of vitamin D. The report further says that the race of the people also plays a significant role.

The findings of the study reveal that patients who have normal levels of vitamin D and progressively higher levels of daytime sleepiness lose vitamin D progressively. Among patients with vitamin D deficiency, sleepiness and vitamin D levels were associated only among black people, Medical Xpress reported.

Among black patients, it was observed that those with higher vitamin D levels also had higher levels 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," said David McCarty, MD, the study's principal investigator.

"It's important to now do a follow-up study and look deeper into this correlation.

For the study, the researchers analyzed a consecutive series of 81 sleep clinic patients with sleep problems and nonspecific pain. With the diagnosis, it was determined that all the patients had sleep disorder and the majority suffered from obstructive sleep apnea.

The levels of vitamin D were determined by blood sampling, and sleepiness with the Epworth Sleepiness Scale.

The authors note that it is logical for a person's race to affect this correlation because increased skin pigmentation is known to cause low levels of vitamin D. The study did not examine causality but the authors' previous studies and current research suggest that lower levels of vitamin D may cause or contribute to excessive daytime sleepiness, either directly or by means of chronic pain.

The study appears online in the Dec. 15 issue of the Journal of Clinical Sleep Medicine.