For some time and for no explicable reason, people have not been able to fall asleep and stay asleep with a full moon in the sky.

According to BBC News, 33 volunteers participated in a sleep study in a tightly controlled laboratory to measure the phenomenon. The volunteers took longer to fall asleep and had a poorer quality sleep with a full moon in the sky, even though they slept in a darkened room.

The body produces a hormone called melatonin, which is linked directly to internal body-clock cycles, when it is dark and makes less when it is light.

However, Switzerland's Basel University professor Christian Cajochen and his colleagues do not believe inability to sleep during a full moon is related to light. The volunteers did experience a drop in melatonin despite sleeping in a dark room.

The study, published in Current Biology, noted that too much light at nighttime and too light during the day can throw off melatonin cycles.

"The lunar cycle seems to influence human sleep, even when one does not 'see' the Moon and is not aware of the actual moon phase," Cajochen said.

The volunteers were not told of the study's purpose and were closely monitored in a sleep lab for two nights while they could not see the moon from their beds. In addition to melatonin dipping, brain activity related to deep sleep fell by a third.

The study concluded that some people may just be acutely sensitive to lunar activity. The researchers also did not originally mean to come upon the results they found. The team looked at old data from a previous sleep study and factored in whether the moon in the sky was full or not.

"There is a such a strong cultural story around the full Moon that it would not be surprising if it has an effect," U.K. sleep expert Dr. Neil Stanley said.

He noted that the results were a small sample size, but could be significant nonetheless.

"It's one of these folk things that you would suspect has a germ of truth," Stanley said. "It's up to science now to find out what's the cause of why we might sleep differently when there's a full Moon."