OFFER TO PURCHASE FOR CASH
                     ALL OUTSTANDING SHARES OF COMMON STOCK
                                       OF
                              REXALL SUNDOWN, INC.
                                       AT
                              $24.00 NET PER SHARE
                                       BY
                           NUTRICIA INVESTMENT CORP.
                     AN INDIRECT WHOLLY OWNED SUBSIDIARY OF

                            KONINKLIJKE NUMICO N.V.
                                 (ROYAL NUMICO)

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          THE OFFER AND WITHDRAWAL RIGHTS WILL EXPIRE AT 12:00 MIDNIGHT,
    NEW YORK CITY TIME, ON FRIDAY, JUNE 2, 2000, UNLESS THE OFFER IS EXTENDED.

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To Our Clients:                                                      May 5, 2000

    Enclosed for your consideration is an Offer to Purchase dated May 5, 2000
(as amended or supplemented from time to time, the "Offer to Purchase"), and the
related Letter of Transmittal (the "Letter of Transmittal," which, together with
the Offer to Purchase, as each may be amended or supplemented from time to time,
collectively constitute the "Offer") relating to the Offer by Nutricia
Investment Corp., a Florida corporation (the "Purchaser") and an indirect wholly
owned subsidiary of Koninklijke Numico N.V., a corporation incorporated under
the laws of the Netherlands ("Numico"), to purchase all outstanding shares of
common stock, par value $0.01 per share (the "Shares"), of Rexall Sundown, Inc.,
a Florida corporation (the "Company"), at $24.00 per Share, net to the seller in
cash, without interest thereon, on the terms and subject to the conditions set
forth in the Offer.

    Also enclosed is the letter to the shareholders from the President and Chief
Executive Officer of the Company, accompanied by the Company's
Solicitation/Recommendation Statement on Schedule 14D-9.

    THIS MATERIAL IS BEING SENT TO YOU AS THE BENEFICIAL OWNER OF SHARES HELD BY
US FOR YOUR ACCOUNT BUT NOT REGISTERED IN YOUR NAME. WE ARE (OR OUR NOMINEE IS)
THE HOLDER OF RECORD OF SHARES HELD BY US FOR YOUR ACCOUNT. A TENDER OF SUCH
SHARES CAN BE MADE ONLY BY US AS THE HOLDER OF RECORD AND PURSUANT TO YOUR
INSTRUCTIONS. THE LETTER OF TRANSMITTAL IS FURNISHED TO YOU FOR YOUR INFORMATION
ONLY AND CANNOT BE USED TO TENDER SHARES HELD BY US FOR YOUR ACCOUNT.

    We request instructions as to whether you wish us to tender on your behalf
any or all the Shares held by us for your account, pursuant to the terms and
conditions set forth in the Offer.

    Your attention is directed to the following:

    1.  The Offer price is $24.00 per Share, net to the seller in cash, without
       interest thereon, upon the terms and subject to the conditions of the
       Offer.

    2.  The Offer is being made for all outstanding Shares.

    3.  The Offer is conditioned upon, among other things, (i) there being
       validly tendered and not withdrawn prior to the expiration of the Offer,
       a number of Shares equivalent to a majority of the total issued and
       outstanding Shares on a fully diluted basis as of the date such Shares
       are

       purchased pursuant to the Offer (the "Minimum Condition") and (ii) the
       expiration or termination of any applicable writing period under the
       Hart-Scott-Rodino Antitrust Improvements Act of 1976, as amended. The
       Offer is also subject to certain other conditions described in
       Section 12 of the Offer to Purchase.

    4.  The Offer is being made pursuant to an Agreement and Plan of Merger (the
       "Merger Agreement"), dated as of April 30, 2000, by and among the
       Company, Numico and the Purchaser. The Merger Agreement provides that,
       among other things, following the consummation of the Offer and the
       satisfaction or waiver of the other conditions set forth in the Merger
       Agreement, the Purchaser will be merged with and into the Company (the
       "Merger"). Pursuant to the Merger Agreement, each issued and outstanding
       Share (other than Shares owned by the Company, Numico or the Purchaser or
       Shares that are held by shareholders exercising dissenters' rights under
       Florida law) shall, by virtue of the Merger and without any action on the
       part of the holder thereof, be converted into and represent the right to
       receive an amount in cash, without interest thereon, equal to the price
       paid for each Share pursuant to the Offer.

    5.  The Board of Directors of the Company has unanimously determined that
       each of the Offer and the Merger are fair to, and in the best interests
       of, the shareholders of the Company, has approved the Merger Agreement
       and the transactions contemplated therein, including the Offer and the
       Merger, has declared that the Merger Agreement is advisable, and
       recommends that shareholders tender their shares pursuant to the Offer.

    6.  Any stock transfer taxes applicable to a sale of Shares to the Purchaser
       will be borne by the Purchaser, except as otherwise provided in
       Instruction 6 of the Letter of Transmittal.

    7.  Tendering shareholders will not be charged brokerage fees or commissions
       by the Dealer Manager, the Depositary, or the Information Agent or,
       except as set forth in Instruction 6 of the Letter of Transmittal,
       transfer taxes on the purchase of Shares by Purchaser pursuant to the
       Offer. However, federal income tax backup withholding at a rate of 31%
       may be required, unless an exemption is provided or unless the required
       taxpayer identification information is provided. See Instruction 9 of the
       Letter of Transmittal.

    Your instructions to us should be forwarded promptly to permit us to submit
a tender on your behalf prior to the Expiration Date.

    If you wish to have us tender on your behalf any or all of the Shares held
by us for your account, please so instruct us by completing, executing,
detaching and returning to us the instruction form contained in this letter. An
envelope in which to return your instructions to us is enclosed. If you
authorize tender of your Shares, all such Shares will be tendered unless
otherwise indicated in such instruction form. YOUR INSTRUCTIONS SHOULD BE
FORWARDED TO US IN AMPLE TIME TO PERMIT US TO SUBMIT A TENDER ON YOUR BEHALF
PRIOR TO THE EXPIRATION DATE.

    In all cases, payment for Shares accepted for payment pursuant to the Offer
will be made only after timely receipt by Wilmington Trust Company (the
"Depositary") of (a) certificates for (or a timely Book-Entry Confirmation (as
defined in the Offer to Purchase) with respect to) such Shares, (b) a Letter of
Transmittal (or a manually signed facsimile thereof), properly completed and
duly executed, with any required signature guarantees, or, in the case of a
book-entry transfer effected pursuant to the procedure set forth in Section 3 of
the Offer to Purchase, an Agent's Message, and (c) any other documents required
by the Letter of Transmittal. Accordingly, tendering shareholders may be paid at
different times depending upon when certificates for Shares or Book-Entry
Confirmations with respect to Shares are actually received by the Depositary.
UNDER NO CIRCUMSTANCES WILL INTEREST BE PAID ON THE PURCHASE PRICE FOR SHARES,
REGARDLESS OF ANY EXTENSION OF THE OFFER OR ANY DELAY IN MAKING PAYMENT PURSUANT
TO THE OFFER.

    The Offer is not being made to, nor will tenders be accepted from, or on
behalf of, holders of Shares in any jurisdiction in which the making or
acceptance of the Offer would not be in compliance with the laws of such
jurisdiction. In any jurisdiction where the securities or blue sky laws require
the Offer to be made by a licensed broker or dealer, the Offer will be deemed
made on behalf of the Purchaser by Salomon Smith Barney Inc., the Dealer Manager
for the Offer, or one or more registered brokers or dealers that are licensed
under the laws of such jurisdiction.

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          INSTRUCTIONS WITH RESPECT TO THE OFFER TO PURCHASE FOR CASH
                     ALL OUTSTANDING SHARES OF COMMON STOCK

                                       OF

                              REXALL SUNDOWN, INC.

    The undersigned acknowledge(s) receipt of your letter, the Offer to Purchase
dated May 5, 2000 (as amended or supplemented from time to time, the "Offer to
Purchase"), and the related Letter of Transmittal (the "Letter of Transmittal,"
which, together with the Offer to Purchase, as each may be amended or
supplemented from time to time, collectively constitute the "Offer") relating to
the Offer by Nutricia Investment Corp., a Florida corporation and an indirect
wholly owned subsidiary of Koninklijke Numico N.V., a company incorporated under
the laws of the Netherlands, to purchase for $24.00 per Share, net to the seller
in cash, without interest thereon, all outstanding shares of common stock, par
value $0.01 per share (the "Shares"), of Rexall Sundown, Inc., a Florida
corporation.

    This will instruct you to tender to the Purchaser the number of Shares
indicated below held by you for the account of the undersigned, on the terms and
subject to the conditions set forth in the Offer to Purchase and the related
Letter of Transmittal.


                                            
Number of Shares to be Tendered:*              SIGN HERE:

 Shares
Account Number:

Daytime Area Code and Tel. No.                 Signature(s)

Taxpayer Identification No. or Social
Security No.

Dated: , 2000
                                               (Please print name(s) and address(es))


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*   Unless otherwise indicated, it will be assumed that all your Shares held by
    us for your account are to be tendered.

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