Berkshire Hathaway's $1.6 billion stake in UnitedHealth Group is helping to lift the Dow Jones Industrial Average to a new record as investors pile into healthcare sector funds.

Shares of UnitedHealth Group surged nearly 14% on Friday after billionaire Warren Buffett's Berkshire Hathaway bought 5 million shares of the company, providing a shot in the arm for investors who think the health conglomerate will turn around under its new CEO.

Berkshire Hathaway revealed four new investments Thursday in steelmaker Nucor, insurer UnitedHealth and two of the nation's biggest homebuilders — Lennar and DR Horton — but it's not clear if the investments are big enough to ensure that legendary investor Warren Buffett handled them.