It's not that doctors are terrible slackers. Average hours dropped from about 55 to 51 hours per week from 1996 to 2008, according to the analysis, appearing in Wednesday's Journal of the American Medical Association.
That's the equivalent of losing 36,000 doctors in a decade, according to the researchers. And it raises policy questions amid a looming primary care doctor shortage and Congress considering an expansion of health insurance coverage that would mean more patients.
The decline in hours "occurred among all groups of physicians young, old, men, women, residents and nonresidents and it didn't occur in other occupations," said lead author Douglas Staiger, an economics professor at Dartmouth College.
"Something has been discouraging physicians from working the long hours they used to work," he said.
Work-hour limits for residents, or doctors in training, were introduced in 2003 and brought down the average. But when researchers removed the resident doctors from the analysis, they still found a nearly 6 percent decline in work hours.
Growing numbers of women in the profession contributed to the decline in hours, but they weren't a big driver of the trend, Staiger said.
Payment issues may have played more of a role. The overall decrease in hours coincided with a 25 percent decline in pay for doctors' services, adjusted for inflation. And when the researchers looked closely at U.S. cities with the lowest and highest doctor fees, they found doctors working shorter hours in the low-fee cities and longer hours in the high-fee cities.
Greater competition and more managed care in the low-fee cities may provide a clue to why doctors are working fewer hours.
"It's not so much the fees as the hassle factor," said Dr. Robert Perlmuter, a Chicago internist, who works 60 hours a week. He told about a recent problem with a pharmacy benefit manager. A series of faxes and phone calls got conflicting answers about which of three types of insulin the patient's plan would cover. By the time it was sorted out, "the patient missed insulin for a day."
"There's so much oversight for what we do, so many people we have to answer to and so little of it improves care, it's just driving us all crazy," Perlmuter said.
Four years ago, Dr. David Ellington, a family doctor in Lexington, Va., cut back from 65 to 50 hours a week, improving his life "by a factor of about a zillion."
"It added five or six years onto my practice life and I love what I do," Ellington said. "I couldn't have continued to do what I was doing. I couldn't do it physically, emotionally and financially. It had become overwhelming."
The researchers based their analysis on data from U.S. Census Bureau household surveys. The data included self-reported hours from about 27,000 doctors. The study was supported by a grant from the National Institute on Aging.
"This really presents a problem for us as a country as we strive to maintain a sufficient primary care work force," said Dr. Ann O'Malley of the nonpartisan Center for Studying Health System Change, which has found declines over the past decade of about two hours per week in doctor work time.
The center's surveys add a piece to the puzzle. They've found overall work hours for primary care physicians and medical specialists declining, but hours worked by surgeons remaining stable, said O'Malley who wasn't involved in the new study.
On top of that, fewer medical students are choosing primary care and more are pursuing higher paying specialties. Paying primary care doctors for the time they spend coordinating care, such as talking to other doctors and avoiding duplicative tests, could help, she said.
Primary care doctors handle 2,300 patients on average, far too many for them to be able to realistically follow guidelines for managing their patients' chronic illnesses, let alone their acute care needs, said Dr. Thomas Bodenheimer of University of California, San Francisco. He wasn't involved in the new analysis but studies work force issues in primary care.
"It's just too many patients to take care of," Bodenheimer said. "And you don't make that much money for each visit. It's really exhausting. It's extremely hard work."