In a given week, Dr. Kim Buck might work 84 hours. During the next six days, she works none. 

The 52-year-old veterinarian works overnights in an emergency practice in San Antonio, Texas, completing a 15-hour shift every Friday and two 12-hour shifts every other weekend. She has Mondays and Tuesdays off followed by three more 15-hour shifts. Buck then has six days of rest, but by her third day off, she has difficulty sleeping.

Despite efforts to maintain her nighttime schedule at home, the quality of Buck's daytime sleep diminishes.

What Buck likely is experiencing, sleep specialists say, is called shift worker syndrome — a sleep disorder characterized by insomnia and excessive sleepiness due to an interruption of the body's circadian rhythms. Common among those who work overnight hours, shift worker syndrome has been known to wreak havoc on the health and productivity of workers across all employment sectors.

Given that the need for medical care doesn't end at 5 p.m., Buck likely has plenty of sleep-deprived colleagues — veterinarians and veterinary staff who burn the candle, so to speak, at both ends. 

"If the shift worker is never able to get fully adequate sleep, all of the various risk impacts associated with inadequate sleep come into play,” said psychologist Timothy Roehrs, director of research at the Henry Ford Sleep Research Center and a professor of psychiatry and behavioral neurosciences at Wayne State University's School of Medicine in Detroit. “Relative to the day-working population, there might be increased pain, exacerbation of other medical disorders or presentation of various medical disorders."

A study published in 2012 in Sleep Medicine Reviews links disruption of the human circadian time organization to an array of jet-lag-like symptoms "and in the long run it may contribute to weight gain/obesity, metabolic syndrome/type II diabetes and cardiovascular disease."

"Epidemiologic studies also suggest increased cancer risk, especially for breast cancer, in night and rotating female shift workers," the study continued. 

Such findings have Buck concerned.

"I've seen all these studies about how it affects your life and it's not as good for you, but when you're young you think you will live forever," she said. "Now I keep reading all this stuff and wondering, 'Am I really shortening my life?' "

The fight for sleep among shift workers tends to worsen with age, experts say.

Buck reports that her younger colleagues find it easy to get shut-eye after an overnight shift, while she finds it difficult to decompress after arriving at home at 9 a.m. On weekdays, she barely has enough time to sleep because her next shift starts at 5 p.m. On weekends, her shift begins three hours later. 

Working more than scheduled can lead to burnout and mistakes, Buck acknowledged. She's permitted to sleep on the job when she can, but it throws off her sleep cycle during the day. 

While there are ways to cope with shift work, there is no permanent fix for those who continually are deficient in sleep, Roehrs said.  

The prevalence of tired workers could be on an upswing in the veterinary profession.

Dr. Gary Stamp, executive director of the Veterinary Emergency Critical Care Society, said he can't pinpoint how many veterinarians and veterinary staff work at night. However, the group's membership numbers have surged, and most emergency veterinary facilities are overnight operations.

"Over the last 10 years our membership has doubled from 2,000 to 4,000,” Stamp said. “About 800 of those are technicians. Attendance has doubled at our national meeting."

Stamp notes that although 24-hour and overnight emergency practices are the norm, some day practices exist, making it impossible to estimate how many shift workers are in the veterinary profession based on the group's membership.

What's more, veterinarians do not have to work in emergency practices to face sleep issues. Dr. Jean Feldman is a solo practitioner in large animal medicine near Buffalo, N.Y., and she's no stranger to pulling all-nighters.

Feldman, 57, gets called out in the middle of the night less often than in previous years because she has trained her clients not to call unless a case is life-threatening. Still, she estimates that she went out on 30 or 40 nighttime emergencies last year.

After wrapping up a colic case at 11 p.m., she might tell the client to phone her at 6 a.m. with an update on her patient's condition.

"If the horse is good, fine. If not, you get up and put on your clothes, and go and do what those people expect," she said.

As a younger veterinarian, Feldman often worked overnight shifts in an emergency practice and then went straight to work in a small animal clinic. Her lack of sleep wouldn't take its toll until the next afternoon.

"I would say that was the point at which I saw that my ability tended to tank," she said. "What I would do is I would be willing to do an all-nighter, and then go to the small animal clinic, and make sure I didn't have call so I could sleep in." 

Feldman still can stay up all night, but she doesn't like it. At the same time, she's unconcerned about the potential long-term impacts tied to sleeplessness.

“I'm sure there might be some health risks involved,” Feldman said, “but hell, I don't see anybody stopping drinking and smoking, and those are much bigger health risks.”