The age of your doctor may impact the quality of the care you receive—and even cut your chances of survival—researchers report in the British Medical Journal.

Harvard researchers looked over data on more than 700,000 hospital admissions of elderly patients cared for by nearly 19,000 physicians between 2011 and 2014. They found that mortality rates crept up in step with physician age.

Patients with doctors under the age of 40 had a 30-day mortality rate of 10.8 percent. With doctors aged 40 to 49, mortality rates inched up to 11.1 percent, then to 11.3 percent with doctors 50 to 59, and 12.1 percent with doctors aged 60 or above.

The stats are adjusted for a variety of variables, such as hospital mortality rates and severity of patients’ illnesses. All the patients were aged 65 or older and on Medicare.

Though the age-related mortality trend was significant overall, it broke down when researchers sorted doctors by caseloads. Older doctors who saw high volumes of patients didn’t see their patients' mortality rates increase.

The study is an observational one—it’s noting a correlation and can’t determine that age is the cause of the different mortality rates. To explain the connection, authors say several factors could be at play. For instance, doctors’ skills may deteriorate over time or simply become outdated. Older doctors may be more likely to rely on anecdotal rather than evidence-based practices. The flip-side is that younger doctors are freshly trained in the most effective practices.

The authors, led by public health expert Yusuke Tsugawa of Harvard, note that:

Hospital medicine is among the most rapidly evolving specialties within medicine, with dramatic changes in the training of recent cohorts of physicians who now work as hospitalists, including greater emphasis on multi-professional team based practice, adherence to clinical guidelines, training on patient handoffs, familiarity with shift work during residency training, and an improved hospital safety culture.

Older doctors who see a lot of patients may be forced to keep up with the most up-to-date methods. Conversely, they may get more patients because they keep up.

While the authors acknowledge that their study is “exploratory,” they stress that health outcomes, like mortality, should be a key driver in the evolution of medicine. The findings, they conclude, “suggest that continuing medical education of physicians could be important and that continual assessment of outcomes might be useful.”

BMJ, 2017. DOI: 10.1136/bmj.j1797 ( (About DOIs).