The Carlyle Group plans to acquire all of NBTY's outstanding shares for $55 per share, a 47% premium above the stock's closing price of $37.47.
NBTY, based in Ronkonkoma, N.Y., makes nutritional supplements and vitamins under the brands Nature's Bounty, Vitamin World and others.
In the fiscal second quarter, its net income doubled but fell short of expectations. Revenue rose 18 percent to $705.1 million. The company has a market capitalization – the total dollar market value of all of a company's shares – of about $2.38 billion.
Private-equity deals were scarce during the recession but have increased in 2010.
NBTY said its board of directors have approved the deal. NBTY is permitted to solicit other proposals for a certain period of time. The deal is expected to close by the end of the year.
"We will leverage Carlyle's global resources and consumer sector knowledge to further drive the Company's global growth," said NBTY chairman and CEO Scott Rudolph.