352 People, Three Months, One Quiet Question

The question the researchers were asking was simple, but I had not heard it asked this way before.

If your mind keeps circling the same dark groove, can a small daily habit on your phone help you find a different one?

That is the study, in one sentence (Kalon et al., 2025).

Who Was in the Study

The research team, led by Lina Kalon at Leuphana University in Germany, recruited 352 adults from the general population. Not a clinical sample. Not people in therapy. Regular adults who agreed to be in a study about a phone-based gratitude practice.

About a third of them — 35 percent — screened positive for depression at the start. So the sample was a mix. Some people were doing fine. Some were not. That mix turned out to matter.

Half the group got the gratitude app right away. Half were put on a waitlist and would get it later. Both groups could keep doing whatever else they were doing for their mental health — therapy, medication, anything. The question was just whether adding a small gratitude practice on top made a difference.

What People Actually Did

The app was simple. People were asked to collect moments of gratitude. Sometimes a written note. Sometimes a photo of something that caught their eye. The team called these moments — small, captured pieces of a regular day. The thing your friend said. The light through the window. The walk that helped.

People could share these with one person they chose, if they wanted. Most just kept them.

That is the whole intervention. Not a workbook. Not a therapy course. A small phone-based habit, kept for a few weeks.

This was not the first study to try this kind of approach. An earlier 2019 trial by the same lab had tested a longer five-week internet and app-based gratitude program (Heckendorf et al., 2019). That study found people in the gratitude group reported less of the looping thinking afterward, with effects that were still visible six months later. A follow-up trial in 2024 tested a multicomponent gratitude program with 200 adults and found similar quieting of the loops, holding up at six-month follow-up (Heckendorf et al., 2024).

So the new 2025 study was building on a foundation that already existed.

What They Measured

The main thing the team measured was the loop. Specifically, repetitive negative thinking — the same thinking pattern from chapter one, measured with a careful questionnaire. They measured it before the study, after four weeks, and again at three months.

Symptoms of depression were measured as a secondary outcome.

What They Found

The numbers, in plain words: people who used the gratitude app reported quieter loops than people on the waitlist. The effect was modest in size. It would not look impressive on a graph in a wellness ad. But it was real and it held up at the three-month follow-up.

Then the researchers looked closer.

When they split the group by who had been in worse shape at the start, the picture changed. The people who had screened positive for depression at the start of the study showed a bigger benefit than the people who had not. About half of an effect size for the depressed subgroup. About a third of an effect size for everyone else. The same pattern showed up for depression symptoms — people who started off heavier got more relief from the practice than people who started off lighter (Kalon et al., 2025).

Put another way. The gratitude app did the most good for the people who were carrying the most.

The Bridge

This is the finding I keep returning to. It is the opposite of how gratitude practices are usually pitched. The next chapter is about why I think it makes sense — and what it suggests gratitude actually is.

References

Heckendorf, H., Lehr, D., Ebert, D. D., & Freund, H. (2019). Efficacy of an internet and app-based gratitude intervention in reducing repetitive negative thinking and mechanisms of change in the intervention's effect on anxiety and depression: Results from a randomized controlled trial. Behaviour Research and Therapy, 119, 103415.

Heckendorf, H., Lehr, D., & Freund, H. (2024). Effectiveness of a guided multicomponent internet and mobile gratitude training program — A pragmatic randomized controlled trial. Internet Interventions, 38, 100780.

Kalon, L. S., Freund, H., Rinn, A., Watkins, P. C., Zarski, A. C., & Lehr, D. (2025). Effectiveness of a gratitude app at reducing repetitive negative thinking as a transdiagnostic risk factor in the general population: Results from a pragmatic randomized controlled trial. Journal of Affective Disorders, 389, 119664.