An overnight shift that starts after midnight may help workers feel less tired, a study suggests.

A research summary to be presented Tuesday at the annual meeting of the Associated Professional Sleep Societies in San Antonio, Texas, predicts minimum on-the-job fatigue for different shifts, based on a mathematical model of sleep time outside of work.

There was a relatively sudden decrease in predicted fatigue for work schedules starting after midnight compared with shifts that had workers clock in just before midnight.

That's because work schedules with start times after midnight allowed workers to get more high-quality sleep before going to work, said study lead author Angela Bowen, a research assistant with the Sleep and Performance Research Center at Washington State University Spokane.

But if a shift starts at 11 p.m., it is less likely that someone would get good quality sleep and be better rested for work.

Shifts that started just before midnight did not allow for pre-shift sleep because that timing conflicts with the body's early evening circadian rhythm, which is set with light exposure.

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Do you experience on-the-job fatigue? If you have a late-night shift, do you think it would make a difference if you started before or after midnight?

(This poll is not scientific. It is based on readers' votes.)