Investigators have in recent weeks been interviewing healthcare industry representatives in sectors where UnitedHealth competes, including doctor groups, the report said. During their interviews, investigators have asked about issues including certain relationships between the company's UnitedHealthcare insurance unit and its Optum health services arm, which owns physician groups, among other assets. UnitedHealth's unit, Optum Health, offers a range of healthcare solutions, from pharmacy benefit management to financial consultation and mental health support.