Gratitude used to be merely an emotion, expressed spontaneously or in accordance with protocol by way of thank-you notes, and discussed in depth only on Thanksgiving, if at all.

Now, it’s also an industry.

Gratitude, commoditized, can be purchased in the iTunes store, where dozens of apps promise better living through gratitude. Oprah Winfrey long advocated keeping a gratitude journal, and now you can buy any number of notebooks designed for that very purpose. (One, by Philadelphia executive coach Shannon Cassidy, is a daunting five-year Grounded in Gratitude journal, marketed with the promise: “One line a day. That’s all it takes to gain the energy associated with gratitude.”) That’s not to mention the self-help section at bookstores, where gratitude is a prescribed path to happiness and health.

Gratitude communication now is also a field of study — one in which academics analyze the best ways to express thanks and the impact of people such as Douglas Conant, the former Campbell Soup Co. chief executive known for writing 30,000 thank-you notes to his employees. Gratitude gurus say deploying it consciously can improve your relationships, your workplace — and maybe even your quality of life.

“Expressing thanks can seem like the most obvious and easy thing in the world. On the other hand, it’s an art,” said Ross Brinkert, an associate professor of corporate communication at Pennsylvania State University’s Abington campus who studies gratitude communication.

advertisement | advertise on newsday

If Google searches are an indication, interest in gratitude has been growing slowly for years.

Psychologists have found correlations between gratitude and improved physical and mental health, empathy and even sleep quality.

Robert Emmons, a University of California, Berkeley, psychologist, has asked more than a thousand people to keep gratitude journals for his studies on the topic. The results of the practice, he reports, range from a stronger immune system and lower blood pressure to increased optimism and happiness.

It’s also, increasingly, seen as a core business practice, according to Brinkert.

Conant, who now runs a Philadelphia leadership consultancy, said expressing gratitude was a key to turning around Campbell Soup, which was struggling when he took the reins of the company in 2001.

@Newsday

He said managers tend to focus on fixing what’s broken and forget to celebrate successes. So he started writing thank-you notes — 10 or 20 of them each day, by hand, during his train ride home — to company staffers.

“I wanted them to know it was from me, that I was personally paying attention,” he said. “What I found is, the more I say, ‘Thank you for a job well done,’ the more engaged the people I work with become; the more they celebrate the contributions of their peers.”

In other words: Gratitude can be contagious.

His No. 1 pro tip: When you say thank you, mean it. “People can tell when you don’t,” he said.

And, as much as gratitude is a management tool, he said, “You’ve got to be one with the message. I don’t think you can compartmentalize.”

advertisement | advertise on newsday

That means living in gratitude not just on holiday and not just during the workday, but all the time.

For Conant, that extends to his personal life. “I don’t think a day goes by where I’m not expressing gratitude to the people I live with in some kind of personal way,” he said. He writes his children letters each Christmas, recapping the past year and celebrating their lives.

If that sounds daunting, start small. Cassidy, the executive coach, tells her clients to try substituting the phrase “get to” for “have to” when going about their lives.

“Instead of, ‘I have to go pick up my kids,’ it’s ‘I get to go pick up my kids,’ ” she said. “That one word changes the whole experience. It’s not like it’s all joyful — sometimes it’s hard — but you can still be grateful for it.”

That’s why she made the one-line-a-day gratitude journals for her clients at Bridge Between, her leadership consulting firm: to get them to set aside a few minutes each day to consider all that’s going right in their lives. The book was so popular she made more of them to sell online.

advertisement | advertise on newsday

For Cassidy, gratitude is the antidote to ruminating on regrets and wrongs.

“It’s the ticket to a more resourceful way of approaching your life and your work,” she said.