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New research at Massey University will provide another piece in the puzzle of why some people are a "morning person" and others a "night person".

Sleep/wake researcher Sarah-Jane Paine has 60 volunteers who have agreed to spend a night in Massey's "isolation facility" to test their body clocks.

The isolation research facility has no clocks, no radios, very little light and only movies to watch on DVD, leaving the volunteers' individual body clocks in sole charge of when they sleep and when they wake.

The 30 self-described morning people and 30 who say they are night people will be tested for melatonin levels through saliva secretion every half hour to measure their body clocks.

Melatonin is a hormone secreted in the brain. When levels are high, you feel sleepy, when low, you are most awake.

"We used to think "morningness" or "eveningness" was a personal thing, similar to whether you were shy or outgoing," Ms Paine said. "But more and more research is showing it's to do with our circadian clock."

"You can see that with a morning person, their melatonin levels go up at an earlier time than an evening person and we think the levels going up is related to wanting to go to bed at an earlier time."

The study is the first of its type in New Zealand and the first internationally using people aged in mid-life.