Gull Holdings and Unity Acquisition Corp. said Monday that they have boosted their offer to buy the outstanding shares of USANA Health Sciences Inc. to $28 per share.

The companies previously had offered $26 per share. They described the new offer as "the purchasers' best and final offer" and extended the offer to midnight July 14.

Through Gull and Unity, a group of investors led by USANA chairman and chief executive officer Myron Wentz wants to buy the outstanding shares in a move to take the company private. Wentz controls Gull, and Gull and its affiliates control about 68 percent of USANA common stock.

A special committee of the USANA board had urged a rejection of the offer, saying the $26-per-share offer was "inadequate and not in the best interests of USANA's shareholders." The offer also had spawned a pair of shareholder lawsuits seeking class-action status and nixing the transaction.

Salt Lake City-based USANA develops and manufactures nutritional, personal-care and weight-management products. Its stock rose 82 cents Monday to close at $26.87. During the past year, the price has ranged from $18.18 to $51.50.