The number of Americans who have a primary care doctor is shrinking -- with potential consequences for their health, researchers say.
Their new study found that in 2015, an estimated 75% of Americans had a primary care provider -- down from 77% in 2002. The declines were most pronounced among people under 60: For Americans in their 30s, for example, the figure dropped from 71% to 64%.
The study, published Dec. 16 in JAMA Internal Medicine, could not dig into the reasons.
But the new "convenience culture" could be one driver of the trend, said lead researcher Dr. David Levine, a physician at Brigham and Women's Hospital in Boston.
Especially for people who are younger and in better health, walk-in clinics -- promising fast service at nontraditional hours -- may be more appealing than an old-style primary care appointment.
"There has been something of a convenience revolution in primary care," Levine said. "And that's likely one of the things going on in younger populations."
If that is the case, is it necessarily a bad thing?
"Continuity of care -- having a provider who knows you, and knows your history -- is very important," Levine said.
In a study published earlier this year, he and his colleagues found that Americans with a primary care doctor were more likely to receive "high-value" types of care.
That, Levine said, includes things like flu shots, counseling on weight loss and smoking cessation, blood pressure checks and standard cancer screening.
There are, however, other culprits in Americans' gradual departure from primary care.
"Everywhere else in the world," Levine said, "'primary care first' is the health care model."
But in the United States, people often see specialists -- who, in the medical world, reign in pay and prestige, Levine noted. And that draws many new doctors into specialties, and away from primary care.
It's known, Levine said, that the nation is facing a shortfall in primary care providers, particularly in rural areas. That's on top of the perennial issue of health insurance, or lack thereof.
"There are definitely intense access issues," Levine said.
The new findings are based on an ongoing federal survey that tracks Americans' health care use.
The number of Americans with a primary care provider fell 2 percentage points between 2002 and 2015.
"Two percentage points might not seem like a big difference," Levine said, "but it translates into millions of Americans."
And some groups -- including the uninsured, younger adults, racial minorities and people in the South -- were more likely than others to lack a primary care doctor. Men were also staying away: By 2015, a full 30% had no provider, compared to 20% of women.
Dr. Ranjit Singh directs the Primary Care Research Center at the University at Buffalo in New York.
He said that access issues, cultural attitudes and the trend toward retail medical clinics could all be contributors.
There might also be some role for "Dr. Google," according to Singh, who was not involved in the study. "Do some people feel they can research their health problem and be their own primary care provider?" he said.
Whatever the reasons, Singh said, "many Americans are missing out on an important opportunity to maintain their health."
Even if you think you're healthy as a horse, he noted, routine primary care visits can catch major conditions that have no symptoms -- like high blood pressure, high cholesterol and type 2 diabetes.
Levine pointed to some potential ways to address the issue.
"We could create incentives for doctors to go into primary care, especially in rural areas," he said. New doctors could, for instance, have their medical school paid for if they agreed to go into primary care in an underserved area for a given number of years.
The field of primary care could also help itself by facing the "convenience factor," Levine said. That could mean offering appointments at nontraditional hours, for example, or using technology to communicate with patients.
The U.S. National Library of Medicine has advice on choosing a primary care provider.