As Americans obsess over personal fitness, weight loss and healthy living, PetSmart is hoping they will do the same for their pets.

The Phoenix-based pet product retailer has entered a partnership with General Nutrition Centers Inc. to develop a line of vitamins and supplements aimed at all stages of a pet’s life.

The products will be manufactured by GNC and sold exclusively at PetSmart retailers beginning this fall, executives said.

Customers at both GNC and PetSmart had been requesting such products, according to Tom Dowd, executive vice president of GNC.

“The new pet vitamins represent a true consumer-driven innovation — we saw the need first-hand in our own stores,” Dowd said in a prepared statement. “With PetSmart’s expertise in pet care and excellent retail capabilities, we knew they were the ideal partner to join us in this venture.”

A PetSmart spokesperson declined to discuss details of the product line.

Pittsburgh-based GNC had $465 million in sales for the first quarter of 2010, an increase of almost 6 percent from first-quarter 2009 sales of $439 million.

PetSmart Inc. had sales of $5.3 billion last year, a 5.4 percent increase from 2008.