UCLA Nobel Prize winner Louis Ignarro acknowledged last week that he should have disclosed to a scientific journal his financial interest in an Herbalife nutritional supplement when he co-authored research that it published on the health benefits of several of the product’s ingredients.

Ignarro, who shared the 1998 Nobel Prize for helping discover the role that nitric oxide plays in cardiovascular health, said that although he still believes he was not ethically required to make the disclosure, in retrospect it would have been better for him and UCLA had he done so.

“No one wants their credibility diminished, especially not a Nobel laureate,” said Ignarro in an interview. “I certainly have learned a lot from all of this.”

Ignarro made his comments after the Proceedings of the National Academy of Sciences published an erratum last month disclosing Ignarro helped develop and market Niteworks, an Herbalife International Inc. product that contains three of four amino acids and vitamins tested in the study, published in May 2004.

The erratum was printed after Bloomberg News distributed a story that revealed a consulting firm founded by Ignarro had received $1 million in royalties from the sale of Niteworks between June 2003 and September 2004.

That disclosure was made in papers filed by Los Angeles-based Herbalife with the Securities and Exchange Commission in preparation for the company’s $201 million initial public offering completed last month.

The study did not specifically test the Niteworks product, but it did conclude that the amino acid l-arginine, vitamin C and vitamin E three key ingredients in Niteworks reduce plaque formations in mice on high cholesterol diets in combination with moderate exercise. Niteworks, which also contains an amino acid called l-citrulline, is marketed to improve cardiovascular health in humans by similarly increasing the supply of nitric oxide. It has never been tested on humans.

Ignarro, who said he was traveling when the Bloomberg article was being prepared and was not interviewed for it, maintained that no conflict existed for several reasons.

He noted he was not the principal author of the study, nor was any of his research money or Herbalife money used to fund it. The principal author was a colleague at the University of Naples, and Ignarro said his role was to review and edit the work.

He added that the study was conceived, carried out and the data collected before he had established his financial relationship with Herbalife, although it was published after the relationship existed.

He said he has asked the editor of the journal, Nicholas Cozzarelli, for a retraction of the errata but his request was refused.

The journal’s managing editor, Bridget Coughlin, said the matter is closed.

A spokesman for Herbalife declined to comment, saying the company was still in a “quiet period” stemming from its December initial public offering.

At UCLA, where Ignarro is a distinguished professor of pharmacology, Vice Chancellor Robert Peccei has been conducting his own inquiry into the matter. Last week, Peccei said he was satisfied with Ignarro’s explanation, though he too said a disclosure should have been made.