There's not much open at night in the quiet Adirondack town where Barnes lives with her husband, daughter, and son. At 1 A.M. on her birthday, Barnes and her daughter went to a 24-hour grocery store to pick up snacks. The only customers there, they treated the aisles like a playground. Barnes would yell loudly from two aisles away: "GENN, I FOUND THE CHIPS!" They ran down the freezer lanes since they're powered by motion lights; Genn stood on the front of the grocery cart with her arms in the air while they belted out the theme song from Titanic. "There are certain freedoms you have in a store at 2 A.M. when everyone else is at home sleeping," says Barnes. "It was the best birthday I've had in a while because someone was with me. I felt less alone in the world."

Barnes has been working the night shift for four years. Before that she was working the "second shift," which runs from around 3 P.M. to 11 P.M. She preferred getting off before midnight and going to sleep when it was dark outside, rather than driving home from work just as the crickets begin chirping. But she felt as if she barely saw her kids. Barnes was leaving for work at 2:30 P.M., just when they got home from school. When a position opened up on the graveyard shift, she jumped on it. The hours seemed perfect: She'd get home from work in time to see her kids off to school in the morning, sleep while they were gone, and wake up just as they got home. She knew it would be an adjustment, but the sacrifices seemed worth it; she wanted to be able to go to every soccer game and recital.

But her body didn't react well to the changes in her schedule. She lives in a constant state of jet lag. One day when she got home from work, her husband told her that there was a small leak in a pipe in the basement and she needed to call a plumber. Barnes nodded. Later, after she awoke, her husband asked when the plumber was coming, and she was dumbfounded. She didn't even remember having the conversation.

Everyone can relate to pushing through the day after a terrible night's sleep. But imagine working all night long and then trying to fall asleep in broad daylight, as lawn mowers are revved, dishwashers are unloaded, and your family putters through the house. When you work the night shift, you're not just losing sleep. "You're fighting against your body's natural circadian rhythms," says David Ballard, the director of the Center for Organizational Excellence and Psychologically Healthy Workplace Program at the American Psychological Association. The body gets confused, he says. Human beings are wired to rest at night and wake up energized. "Lack of sleep causes great in night shift workers," says Ballard. Less apparent but equally deleterious to well-being is the emotional toll of night shift work. "When you work at night, you're cut off from friends and family, you have little social support, your may not be as healthy. When day shift workers get home, we do things that relax us, like go out to eat or grab a drink with a friend. But when you're working the night shift, you lose that. You're facing additional stress, but you have fewer ways to cope with it."

According to the most recent data from the Bureau of Labor Statistics, nearly 15 million Americans work the night shift, and that number is expected to grow. In today's global economy, many of us live within driving distance of a 24-hour Wal-Mart or grocery store. Pilots, nurses and doctors, even janitors like Barnes, have long worked the night shift, but today, the Internet (particularly with the globalization of services) is creating a greater demand for nighttime work—everything from IT specialists monitoring a company's software to security officers keeping that IT office safe. All of this has translated to a demand for round-the-clock workers.

Workers agree to night shifts for a variety of reasons. "It was the only job I could get," says Tracy Jones, who has worked nights as a temp in factories in Milwaukee on and off for a year. "When you've got bills, you're not in a position to be choosy." She takes a 30-minute bus ride across town to work from 11 P.M. to 7 A.M. "After 4 A.M., I'm literally standing on my feet dead asleep, but a job is a job," she says. One nighttime trader on Wall Street said he worked nights for three years to get noticed in a big trading company: "I hated it—my life was upside down —but I knew I was learning a lot and interacting with important clients." Michelle Tam, an overnight pharmacist at a hospital in San Francisco, appreciates the autonomy of working nights. She works 7 P.M. to 7 A.M. for seven days, then she has seven days off.

The long-term physical health effects associated with working nights are well-documented. In 2007, shift work was listed by the World Health Organization's International Agency for Research on Cancer as a "probable carcinogen." Researchers from the Fred Hutchinson Cancer Research Center in Seattle found that women who work the night shift have a 49 percent increased risk of being diagnosed with early-stage ovarian cancer. While no one is sure of the cause, it's thought that suppressed levels of the hormone melatonin put workers at risk. Melatonin production usually occurs at night and is compromised under artificial light. Melatonin in turn regulates pituitary and ovarian including . Elevated levels of estrogen are linked to increased risk of reproductive cancers. Interestingly, shift workers in the study who described themselves as night owls had lower rates of ovarian cancer, suggesting that individuals who sync well with shift work are at lower risk of disease. A 2012 study in the American Journal of Epidemiology reported that men who work at night are three times as likely to develop prostate cancer as are day workers. The ongoing disruption of a person's natural circadian rhythms has also been linked to cardiovascular disease, , digestive problems, and diabetes. One study showed that night shift work contributed to higher rates of heart disease among police officers. Nighttime truck drivers had higher rates of hypertension as well as heart disease.

Physician Alon Avidan, director of the UCLA Sleep Center, says it's not uncommon for shift workers to develop conditions due to accumulated sleep debt. "Things get to a point where it begins to impact their social function and relationships. They might feel depressed or more . We'll see relationships break up or moms or dads not able to fulfill their obligations as parents," he says. Shift workers report that it's their day-to-day life that suffers most, especially since society is built around a 9-to-5 work schedule. You can't go to a medical checkup at nine at night or call an electrician at two in the morning when you're on break. You miss out on barbecues and christenings, school plays and lunch dates. If your boss works days, you may not see him for weeks. You're certainly not in a book club. "Night shift workers begin to feel like second-class citizens," says Carole Lieberman, a psychiatrist on the clinical faculty at UCLA's Neuropsychiatric Institute, who has treated shift workers. "They begin to feel invisible."

Avidan says that he often sees nighttime workers who are struggling to stay awake during their shift. Fatigue often leads to mistakes, and many of his patients are sent to him after getting hurt or putting others in danger. He's treated a nighttime bus driver who was having too many early morning accidents and hospital workers who missed critical steps while performing diagnostic tests. (Val Barnes recently backed into a car at the end of her shift—"I didn't even see it," she says.) Many night workers are diagnosed with Shift Work Disorder, a diagnosis given to anyone who cannot cope with the changes in their . They experience extreme sleepiness, and often and as well. According to Avidan, individuals with Shift Work Disorder are three times more likely to have an accident on the job than are employees who do not work a night shift. Even if they think they're sleeping enough during the day, they may not be getting the sleep they need. Many shift workers get off in the morning, take a one-hour nap to take the "edge" off, then wake up to make breakfast and drive the kids to school. "Maybe they go back to sleep at 10 or 11 A.M., but now their sleep is fragmented," says Avidan. "Sleep has to be taken in one chunk. It's like baking a cake. Instead of leaving it in for an hour, you leave it in for five minutes at a time. Well, then it's never going to bake. When shift workers take a nap and then go back to sleep later, they're not getting the restorative sleep they need to feel recovered." Actually, they may not feel recovered at all unless they stop working the night shift, which is what Avidan always suggests as the first step in treatment.

Accumulated sleep debt takes a toll on an individual's ability to make good decisions, let alone sharp, split-second ones required of nighttime workers in life-and-death situations. Major accidents like the Exxon Valdez oil spill, Three Mile Island, and the meltdown at Chernobyl took place during the night shift. But being on the night shift doesn't just influence reaction times—it changes how we react in challenging situations: One study found that police officers who work the night shift are angrier and more hostile to people they pull over than are daytime officers. "You think you're more competent than you actually are," says Michelle Tam. For this reason, she uses a checklist to double- and triple-check the prescriptions she fills. She'll underline important information —how many pills, the dosage —to make sure that she doesn't forget it minutes later.

Then there are jobs, like flying a jumbo jet or performing open heart surgery, that require the ability to multitask no matter how tired you are. "It's critical to be well-rested in the cockpit because things can change so quickly," says Linda*, an international pilot with FedEx. "If you're not at the top of your game all the time, things can go wrong." Linda, who pilots overnight flights everywhere from Beijing to Brussels, says she keeps a strict sleep schedule, sticking to her Eastern time zone. When abroad, she tries to sleep in four-hour increments whenever she would normally be sleeping at home. She says many pilots have an unspoken honor system: Speak up if you didn't get enough sleep before the flight, so that pilots can swap rest periods with one another if need be (there are four in the cockpit on international runs). Linda's body slows down between 3 A.M. and 5 A.M., when many of her flights land. "Imagine having your natural slowdown at the most important part of the flight," she says. "If you don't find a technique or strategy that works for you sleepwise, you're going into the landing with a deficit."

"Either you change your schedule," Laurie finally told him, "or we're done." Sutermeister worked out a new arrangement with his boss. Even though he still works at night, he's working fewer hours—an 8-hour shift versus a 12-hour shift—which gives him more time to catch up on sleep during the day. His wife says he's much less cranky.

The night shift takes a toll on marriages. Research shows that night shift workers' rates are higher and they report less marital satisfaction than other workers. With one spouse getting home just as the other leaves for work, husbands and wives are less physically and emotionally available to each other. On weekends, the spouse working the night shift tries to catch up on sleep rather than taking the kids to the movies or to the park. And forget chores. Night shift workers report putting off household duties, even those as simple as laundry, because they're fatigued. Often, one partner will begin to feel the division of labor is unequal, and resentment builds.

Cornwell has found that night workers have trouble syncing their schedules with society as well, which impacts their relationships with everyone around them. They're less likely to talk to a neighbor, or go to a restaurant, museum, or sporting event. "Getting a drink is something you do at the end of the day," says Cornwell. "There isn't a social framework that makes sense for people at the beginning of the day. Imagine going to a concert after breakfast?"

Yet everyone makes trade-offs, and many parents interviewed for this story reported that they work the night shift "for their kids." In some families, it seems to pay off. A 2008 study by Sara Raley, a professor of sociology at McDaniel College, found that parents who work the night shift have children "in their orbit" more often than parents who work days, since they tend to be home between 3 P.M. and 6 P.M., when kids return from school. Tam, the nighttime pharmacist, worked nights through two pregnancies. Several years later, she believes she's achieved some semblance of work/life balance even as she continues to work nights. For one, she makes sure that she, her husband, and their two boys eat dinner together before her shift. "I grew up in a family where we all sat down to dinner every night and talked about our day," she says. "We try to keep all of those normal routines, despite my work hours."

Still, the quality of that time is difficult to measure. In a 2013 study of the impact of night shift work on children's behavior, researchers found that when mothers worked the night shift, their kids had elevated levels of aggressive and anxious or depressed behavior. Rachel Dunifon, a professor in the department of policy analysis and at Cornell University who led the study, says she doesn't know why kids of night workers are more apt to struggle, but she's guessing that a lack of sleep is to blame. "If mothers are getting less sleep, they may struggle to effectively manage their child's schedules and routines," she says. "They might have a shorter fuse."

If one parent in a two-parent family works nights, child care is a cinch. But it can be especially challenging for a single mother—and 46 percent of single mothers of young children in one study reported doing shift work or working weekends. The Chambliss Center for Children in Chattanooga, Tennessee, which caters to lower-income families, has offered overnight childcare since the mid-1990s.

At around 6:30 P.M., kids arrive at a classroom to do their homework with staff members; they may also do crafts, read books, play, and watch TV. "We want them to feel comfortable, like they're at home, so we let them watch cartoons before bed," says Tracy Bryant, associate director of the Extended Child Care Center at Chambliss. "This should be their down time."

At 8 P.M., staffers roll cots into the classroom, give each child a blanket and a pillow, and sit with them as they drift off to sleep. Parents pick them up around 5:30 A.M. when their shift ends. "Parents need flexible child care options," says Bryant. "There's a higher demand for this kind of care than many people realize." Some nights, there will be a dozen kids in the overnight room, sometimes two or three.

Bryant says that one mother would pick her kids up at midnight, waking them up to get them home. "It was disrupting their sleep at the moment they needed it most," she says. Moms bring their kids to the overnight program as a last resort—they'd rather their kids sleep at the home of a family member.

One mother, who worked nights as an aide to an elderly woman, was anxious about leaving her daughter to sleep in a strange classroom. She called the staffers every couple of hours to check on her. But her daughter went to sleep easily and slept through the night. "Often, children are more than the parents," says Bryant. "Mom may feel guilty. We had one mom cry with joy after she was transferred to the day shift and could move her daughter back to daycare."

As for Barnes, she says she'll stay in her job as janitor for as long as it makes sense for her kids. It pays well, she says, and she gets great health benefits for her family. Still, she about working days. Says Barnes: "I just want a normal life again."

An Upside To Working Alone

There are quiet benefits to working at night, chief among them a deeper sense of introspection.

Some people enjoy working the night shift—their bodies transition to nights more easily than others', and after many years, their circadian rhythms begin to shift altogether. Even among those who wish for a daytime schedule, there are aspects of working at night that are appealing. For some, the silence is a source of comfort.

When Ramon Zayas, who has been baking every night for the last 40 years, went on vacation with his wife recently, he lay down with her to watch TV until she fell asleep. Then, he tiptoed out of bed and went out sightseeing—in the dark. He couldn't sleep if he tried—he hasn't slept at night in four decades. Plus, he likes how quiet places are at night, how much more you notice when no one else is around. He'll stop to stare at the wind blowing through the trees, watch a fox trot across the road, see the way the homeless settle in for the night. He always looks for bakeries, going around back and knocking on the door to say hello. Back home in Rochester, New York, Zayas says he lives in a "silent world" at night. Until his donut fryer arrives at 3 a.m., it's just him and maybe one other worker.

"I do a lot of sorting out my mind," he says.

Val Barnes says that working in isolation gives her time to decompress. Even as she struggles to stay awake, the silence is comforting, since the rest of the world is turned off. "You can hear almost everything," she says. "I know every groan of the building." She can sense when another janitor is nearby, even if she doesn't hear his footsteps. She can feel the air get cooler if someone opens a door on the other side of the building. "You just become more perceptive," she says. "You're so in tune to your surroundings, like a blind person developing super hearing." You begin to see what you're innately capable of, she believes, and what you're not. You hear your talking to you all night long. Says Barnes: "It brings you to a different level of knowing yourself."