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,

UnitedHealth’s stock cuts the Dow’s price by more than 400 points, as care activity accelerates and Medicare costs remain higher than expected.

UnitedHealth Group said its Chief Executive Andrew Witty resigned as of Tuesday, and the company suspended its annual forecast due to surging medical costs, sending shares plunging nearly 18% to a four-year low.