New Delhi, Aug. 5 -- CINCINNATI - Procter & Gamble announced Monday it had agreed to acquire Thorne, a science-backed supplement brand with a devoted following among healthcare practitioners, for $3.8 billion, the company's most significant health care expansion in years and one its newly appointed chairman disclosed personally to CNBC.

The announcement arrived less than a week after P&G named Shailesh Jejurikar its board chairman, a promotion that concentrated leadership authority at the top of a company now signaling explicitly that health care is not a peripheral portfolio but a primary growth directive. That the chairman chose to deliver the news in a televised interview, rather than through a prepared statement, conveyed how much P&...