Does sticking with the same doctor lead to a longer life?

About 21 percent of Americans do not have a personal doctor.

About 21 percent of Americans do not have a personal doctor, according to the 2016 analysis by the Kaiser Family Foundation, with Alaska topping out at 32.2 percent.

However, a new systematic review suggests that when a person sees the same doctor over time that it can lead to a lower chance of an early death.

The review, a collaboration between the U.K. University of Exeter Medical School and St. Leonard’s Practice in Exeter, analyzed 22 smaller studies from nine different countries. Each of these studies looked at the association between “continuity of care” and death. The U.K. researchers defined "continuity of care" as "repeated contact between an individual patient and a doctor."

About 81 percent of the studies they looked at showed statistically significant reductions in mortality associated with people who were able to see the same doctor over a long period of time.

“We were pleasantly surprised at the results,” Phil Evans, associate professor of general practice and primary care at the University of Exeter Medical School and one of the study authors, told ABC News.

However, the biggest limitation of the study was that the researchers were unable to compile all of the study findings together in what is known as a “meta-analysis,” which would have told them how much the risk decreased. A meta-analysis can’t use studies that are too different from one another, where comparisons can’t be fair. There were different definitions of "continuity of care" and different follow-up periods from study to study. The study authors believe their findings would also apply to America, despite its unique private insurance-based healthcare system.

“We appreciate that the American family practice model is different from the U.K., however, we did include several major U.S.-based studies in our analysis,” Evans told ABC News.

It’s unclear what factors are really behind this trend in lower mortality. It could be that the close contact between patient and physician for an extended period of time means the patient may be more likely to stick with evidence-based preventative medicine like vaccines, and more likely to follow treatment recommendations made by a doctor they’ve gotten to know over the years.

“We can hypothesize why there is an association,” Evans told ABC News. “There is evidence that as patients are more satisfied with their doctor they are more likely to take their advice on screening for instance, such as pap smears for women, or with treatment like taking statins if they are recommended.”

Dr. Ronald Epstein, professor of family medicine, psychiatry, oncology, and medicine at the University of Rochester School of Medicine and Dentistry, who was not involved in the study, noted to ABC News the benefits of keeping the same medical team for both doctors and patients.

Dr. Amitha Kalaichandran is a pediatrics resident doctor working in the ABC News Medical Unit in New York.