The study, published in the Annals of Family Medicine, found that 35 percent of physicians who described themselves as atheist, agnostic or none practiced among the poor compared to 31 percent of physicians who were measured to have "intrinsic religiosity" as well as frequent attendance at religious services.

"This came as both a surprise and a disappointment," study author Dr. Farr Curlin, of the University of Chicago, said in a statement. "The Christian, Jewish, Muslim, Hindu and Buddhist scriptures all urge physicians to care for the poor, and the great majority of religious physicians describe their practice of medicine as a calling. Yet we found that religious physicians were not more likely to report practice among the underserved than their secular colleagues."

Policy makers and medical educators hoping to increase the physician supply for underserved populations should take these results into account cautiously, according to the authors.

"No one knows how to select medical students in a way that would actually increase the number of physicians eager to serve the poor, but our findings suggest that admissions officials should ignore both the general religiousness of candidates and their professed sense of calling to medicine," said Curlin.