Dhaka, May 13 -- UnitedHealth CEO Andrew Witty is stepping down for personal reasons and the nation's largest health insurer suspended its full-year financial outlook due to higher-than-expected medical costs.

Chairman Stephen Hemsley will become CEO, effective immediately, the Minnesota company said.

Hemsley was UnitedHealth Group CEO from 2006 to 2017. He will remain chairman of the company's board. Witty will serve as a senior adviser to Hemsley, AP reports.

"Leading the people of UnitedHealth Group has been a tremendous honor as they work every day to improve the health system, and they will continue to inspire me," Witty said.

Witty joined the company in 2018 after serving about nine years as CEO of the British drugmaker GlaxoSmi...