EX-(a)(3)
                             LETTER TO SHAREHOLDERS

[LOGO]                                                               MAY 5, 2000

                              REXALL SUNDOWN, INC.
                         6111 BROKEN SOUND PARKWAY, NW
                           BOCA RATON, FLORIDA 33487

To the Shareholders of Rexall Sundown, Inc.:

    I am pleased to report that on April 30, 2000, Rexall Sundown, Inc. (the
"Company") entered into an Agreement and Plan of Merger (the "Merger Agreement")
with Royal Numico N.V. ("Numico") and Nutricia Investment Corp., a Florida
corporation (the "Purchaser"). The Merger Agreement provides for the acquisition
of all outstanding shares of Common Stock, par value $0.01 per share, of the
Company (the "Common Stock") by the Purchaser at a price of $24.00 per share,
net to the seller in cash, without interest. Under the terms of the proposed
transaction, the Purchaser has commenced a tender offer (the "Offer") for all of
the outstanding shares of Common Stock at $24.00 per share, net to the seller in
cash, without interest. The Offer is currently scheduled to expire at 12:00
Midnight, New York City time, on Friday, June 2, 2000, unless otherwise
extended.

    Following the successful completion of the Offer and upon approval by a
shareholder vote, if required, the Purchaser will be merged with and into the
Company (the "Merger") and all shares of Common Stock not purchased in the Offer
will be converted into the right to receive, without interest, an amount in cash
equal to $24.00.

    YOUR BOARD OF DIRECTORS HAS UNANIMOUSLY APPROVED THE MERGER AGREEMENT, THE
OFFER AND THE MERGER, DETERMINED THAT THE OFFER AND THE MERGER ARE FAIR TO, AND
IN THE BEST INTERESTS OF, THE HOLDERS OF SHARES OF COMMON STOCK AND RECOMMENDS
THAT ALL HOLDERS OF SHARES OF COMMON STOCK TENDER THEIR SHARES OF COMMON STOCK
PURSUANT TO THE OFFER.

    Accompanying this letter is a copy of the Company's
Solicitation/Recommendation Statement on Schedule 14D-9 and the Company's
Information Statement pursuant to Section 14(f) of the Securities Exchange Act
of 1934, as amended, each filed by the Company with the Securities and Exchange
Commission. The Board of Directors of the Company has received an opinion, dated
April 28, 2000, of Morgan Stanley & Co. Incorporated, financial advisor to the
Company, that the $24.00 per share cash consideration to be paid in the Offer
and the Merger to the holders of shares of Common Stock is fair, from a
financial point of view, to such holders. A copy of this opinion is attached to
the Schedule 14D-9.

    Also accompanying this letter is a copy of the Offer to Purchase and related
materials of the Purchaser, including a Letter of Transmittal for use in
tendering your shares of Common Stock. These documents set forth the terms and
conditions of the Offer and provide instructions for tendering your shares of
Common Stock.

    WE URGE YOU TO READ EACH OF THE ENCLOSED MATERIALS CAREFULLY.

    The management and directors of the Company thank you for the support you
have given the Company.

                                          Sincerely,

                                          /s/ Damon DeSantis

                                          Damon DeSantis
                                          PRESIDENT AND CHIEF EXECUTIVE OFFICER