Jim Underwood's workday begins just as most people come home for the evening.

As the shift supervisor of the University of Tennessee Police Department, Lt. Underwood regularly works from 7 p.m. to 7 a.m.

"I'll go home and I'll go to bed and then get up and maybe do some stuff around the house and go get lunch and do something like that and come back and get ready for work," Underwood said. "The days we work, we work 12-hour shifts. There's not a lot of downtime when you're working the next day ...The longest stretch I work is three days in a row with at least two days off."

In 2011, the American Psychological Association reported that nearly 15 million Americans work night shifts.

Underwood stated that what makes night shifts difficult is deviation from routine, which complicates returning to daytime work.

"I can work night shift and it's fine if I did nothing but come in at seven o'clock at night and worked till seven the next morning, that's fine," he said. "But there's meetings. And the rest of the world rotates around a 9-to-5 schedule ... so if we have a staff meeting here it's during the day. If we have training, it's during the day ... if it's just a one-day training, it's not really that hard. When they send us to something that's like a week-long training session, then it can really be difficult to shift back into that for an entire week."

Although describing himself as a "night owl," Underwood estimated he gets approximately six to eight hours of sleep on average.

However, those hours are not particularly restful.

"It's a lot of times just up and down ... like I said, the world's moving around you ... (but) I feel most of the time that I get plenty of sleep. I'm lucky."

Other than a mild chronic fatigue, Underwood said he hasn't felt effects in more than 20 years working for UTPD.

"There's always just a little nagging fatigue just building in the back of your mind," Underwood said. "Leaving the house today I was kind of like, 'Man, I wish I had gotten another hour of sleep,' but you overcome that. Caffeine helps a little."

Theresa Lee, dean of the College of Arts and Sciences and professor of psychology, said that overnight workers are at risk for physiological effects.

"We now know that (sleep) changes the hormone balance," Lee said. "... It's also very involved in your immune system."

Overnight workers also are not only at risk for getting sick more frequently; they are at a higher risk for more serious diseases.

"You're at higher risk for developing cancer, (and) women have fertility issues," Lee said. "In addition, hormones that have to do with controlling appetite and weight are altered so that the hormone that lets your brain know that you've been eating ... is suppressed.

Lee said that while adjusting to overnight schedules is possible, the human body will suffer.

"The reality is that we aren't built for it," she said. "You need to sleep at the same time everyday ... If you're going to work the night shift, you need to behave as if you live in Europe all the time ... and unfortunately, living in a society when everybody else in your household isn't on that schedule makes it really, really hard. There is no real way out of this."

Thanks to UTPD's leadership, Underwood said that health and job safety risks associated with night shifts are at a minimum.

"They really look after us a lot more than they used to," Underwood said. "I've worked ... 32-36 hours straight in the past. And that's where it gets scary ... but ... they don't do that anymore."