As we launch into Thanksgiving week, consider this: Research shows that feeling grateful doesn't just make you feel good. It also helps — literally helps — the heart.

A positive mental attitude is good for your heart. It fends off depression, stress and anxiety, which can increase the risk of heart disease, says Paul Mills, a professor of family medicine and public health at the University of California San Diego School of Medicine. Mills specializes in disease processes and has been researching behavior and heart health for decades. He wondered if the very specific feeling of gratitude made a difference, too.

So he did a study. He recruited 186 men and women, average age 66, who already had some damage to their heart, either through years of sustained high blood pressure or as a result of heart attack or even an infection of the heart itself. They each filled out a standard questionnaire to rate how grateful they felt for the people, places or things in their lives.

It turned out the more grateful people were, the healthier they were. "They had less depressed mood, slept better and had more energy," says Mills.

And when Mills did blood tests to measure inflammation, the body's natural response to injury, or plaque buildup in the arteries, he found lower levels among those who were grateful — an indication of better heart health.

So Mills did a small follow-up study to look even more closely at gratitude. He tested 40 patients for heart disease and noted biological indications of heart disease such as inflammation and heart rhythm. Then he asked half of the patients to keep a journal most days of the week, and write about two or three things they were grateful for. People wrote about everything, from appreciating children to being grateful for spouses, friends, pets, travel, jobs and even good food.

After two months, Mills retested all 40 patients and found health benefits for the patients who wrote in their journals. Inflammation levels were reduced, and heart rhythm improved. And when he compared their heart disease risk before and after journal writing, there was a decrease in risk after two months of writing in their journals. Those results have been submitted to a journal, but aren't yet published.

Mills isn't sure exactly how gratitude helps the heart, but he thinks it's because it reduces stress, a huge factor in heart disease.

"Taking the time to focus on what you are thankful for," he says, "letting that sense of gratitude wash over you — this helps us manage and cope."

And helps keep our hearts healthy.

Over this past year, lifestyle blogger Aileen Xu has kept a monthly gratitude list.

Sometimes it was the big stuff: "I'm grateful that my family is so understanding. I'm grateful so many people care."

And sometimes it was life's little blessings: "July 2018: I'm grateful for good hair after I shower."

Xu started making such lists when she was in college, "at a point when I was just not in a very good place in my life." Now, the 28-year-old lifestyle blogger and YouTuber recommends the practice to her nearly 750,000 subscribers.

It wasn't a hard sell.

"I think just over the last few years there's been more of a trend to focus on gratitude," says psychologist Laurie Santos, who teaches a course on the science of well-being and happiness at Yale.

Gratitude is being endorsed by wellness blogs and magazines. You can buy different kinds of specific gratitude journals, or download apps that remind you to jot down your blessings.

"Those types of products can remind us to take time to be grateful," Santos says. "But it's also important to remember that gratitude is free."

And noting your gratitude seems to pay off: There's a growing body of research on the benefits of gratitude. Studies have found that giving thanks and counting blessings can help people sleep better, lower stress and improve interpersonal relationships. Earlier this year, a study found that keeping a gratitude journal decreased materialism and bolstered generosity among adolescents.

In another study from August, high school students who were asked to keep gratitude journals also reported healthier eating. There's also some evidence it could lower your risk of heart disease and lower symptoms of depression for some people.

That's why gratitude features heavily in Santos' happiness class. "It's one of the practices that really wins out from the field of positive psychology," she says, because it takes very little time, and "the benefits are so powerful."

Making gratitude lists is one way of accessing those benefits. You could thank God or the universe. You could keep your gratitude private or share it with others. The best way of accessing and expressing gratitude may be different for each person.

Santos' students, in addition to keeping gratitude journals, are asked to write a thank you letter and then read it out loud to the recipient. "I can show measurable improvements in well-being even a month after you've done this," Santos says.

What works for some people may not work for others. To find your best method, "[r]eally think about what feels right and what feels natural or meaningful to you," says Sonja Lyubomirsky, a professor of psychology at the University of California, Riverside, who studies happiness and gratitude.

Some may find that a daily dose of gratitude in the morning can be transformative. "It helps me feel awake and abundantly joyful," says Sam Khazai, a 38-year-old actor based in New York, who uses a journal that prompts him to list three things he's grateful for each day.

"I know it sounds kind of meta," he says. "But practicing gratitude, it brings me so much gratitude in and of itself."

There have been times, however, when he has skipped a day or even several days when he's felt especially down. "Or if I don't skip those days, I've straight up lied to my own gratitude journal ... I've filled it with things I hoped to be grateful for," he says — but he didn't feel grateful, and forcing it felt bad.

"Gratitude is a very rich emotion, but it's also kind of a complicated one," notes Lyubomirsky. "Sometimes when you express gratitude, you could also feel humbled or indebted or embarrassed. So it doesn't always feel pleasant."

In one study Lyubomirsky and her colleagues found that counting blessings once a week boosted happiness, but doing so three times a week didn't. "That suggests that for most people, at least on average, three times a week was too much," she says. "And too much gratitude can sort of backfire."

There's also a lack of research on how gratitude exercises affect people with clinical depression, anxiety or suicidal tendencies, Lyubomirsky says. "If you're depressed, and you're asked to express gratitude ... you might have trouble thinking of what you're grateful for, or you may feel really guilty you haven't paid back that person you're grateful for."

Indeed, for all the research on the broad benefits of expressing gratitude, there's also evidence that it isn't for everyone. And it isn't a panacea — it can't make injustice, loss, or pain disappear.

What gratitude can do is give us hope. "The research shows that focusing on the positive, in addition to the negative, can boost our mood more than we expect," says Santos.

In Oakland, Calif., 31-year-old mental health counselor Zeyda Garcia agrees. During really tough times, like when she'd lost a job and was sleeping on her friend's mom's couch — she felt like she was reaching for reasons to be grateful.

But she still tried to find some. "Even if it's just — I'm grateful for the sun that's shining or being able to wake up," she says. It felt hokey, and "kind of fake, a little bit."

But ultimately, it helped. "It allowed me to ground myself," she says. "It allowed me to remember what was going well, in a world full of chaos."