The sheer number, and the severity, of these other conditions appears to decrease patients' ability to manage their diabetes. The type of co-existing condition also matters, as diabetes self-care lags most among patients with conditions that they think aren't related to their diabetes.

The new findings make it more important than ever, the researchers say, for doctors to "treat the whole person" by helping diabetes patients learn how to deal with their other conditions in ways that will also allow them to control their diabetes.

The study, published online ahead of print in the December issue of the Journal of General Internal Medicine, uses data from a nationally representative sample of 1,901 adults with diabetes who were age 55 or older in 2002.

The researchers, from the University of Michigan Health System and the VA Ann Arbor Healthcare System, looked at the influence that a range of medical conditions had on the participants' ability to manage their diabetes, whether or not those conditions were physically linked to diabetes. For one condition, heart failure, they also assessed how the severity of another condition affected diabetes management.

The data were drawn from the Health and Retirement Study, a major study of older Americans based at the U-M Institute for Social Research and funded by the National Institutes of Health. The current research was funded by VA and NIH.

"Patients are dealing with these issues day to day, and they're affecting the way people prioritize and manage their own self-care," says first author Eve Kerr, M.D., MPH, of the VA and UMHS. "Meanwhile, we physicians talk to patients about their diabetes, but not about how their heart failure or their hypertension is affecting how they manage their diabetes. These results show that we need to be treating the whole patient, but we don't yet have systems designed to do that."

The competing demands of simultaneous chronic diseases may lead people to neglect the self-care steps that will have the biggest impact over the long run, Kerr says. For instance, if a person with diabetes also has arthritis pain, or shortness of breath from heart failure, and these aren't fully addressed, the person may refrain from physical activity. And that in turn means they'll struggle to control their blood sugar or blood pressure - which is important to prevent future issues such as stroke.

In general, the more diseases a person had along with their diabetes, the more likely they were to report they were putting priority on conditions other than their diabetes, and the worse they reported they were doing at managing their diabetes through five key self-care steps. Severity also mattered: For the one condition for which the researchers had severity data -- heart failure -- diabetes self-care was not diminished among patients in the early, less symptomatic stages, but it was among those in later stages.

Also important, the study found, is whether patients perceive that their other conditions are related to their diabetes. For instance, many people with diabetes still don't realize that their disease puts them at much higher risk of heart disease and stroke. That lack of awareness may mean that they don't put as much emphasis on their blood pressure or cholesterol, when in fact controlling those risk factors can greatly influence the health of a person with diabetes. And indeed, in the current study, diabetes self-care was worse among people who had both diabetes and heart disease.

That's why a whole-person approach to care is so important, says Kerr, who is an associate professor of internal medicine at the U-M Medical School and associate director of the VA Health Services Research & Development's Center for Clinical Management Research. So much is known about how to prevent long-term diabetes complications, and how to detect them early when they can still be treated, that the "return on investment" for good diabetes self-care is high.