U.S. nutritional supplements maker NBTY Inc said it agreed to be bought by private-equity firm Carlyle Group for $3.8 billion.

The PE firm's $55.00 a share cash offer represents a 47 percent premium to NBTY's Wednesday close.

NBTY, known for supplements such as Nature's Bounty, Osteo Bi Flex, Ester C and Pure Protein, expects the deal to close by the end of this year.

The Ronkonkoma, New York-based company's board unanimously approved the deal.

The company, which has a market value of about $2.3 billion, posted a quarterly profit in April that missed market expectations by a wide margin, hurt by increased spending on television advertising.

BofA Merrill Lynch and Centerview Partners LLC are acting as financial advisers to NBTY, while Barclays Capital and Credit Suisse will offer financial advice to Carlyle.

NBTY's shares closed at $37.47 Wednesday on the New York Stock Exchange.

(Reporting by Shradhha Sharma in Bangalore; Editing by Vinu Pilakkott)

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