Does writing down what you're grateful for actually make you happier?

Yes, a little. The biggest review so far pooled 145 studies with nearly 25,000 people in 28 countries and found that gratitude exercises, like keeping a gratitude journal or writing thank-you letters, lead to small increases in well-being. Not life-changing on their own, but real, and the result held up when the researchers checked for the usual suspect: studies with disappointing results never getting published.

The early studies sounded more dramatic. In one, people tried six different happiness exercises. The biggest short-term boost came from a gratitude visit: writing a letter of thanks to someone in your life and delivering it. Happiness scores rose by 10 percent and depression scores fell, for up to a month. The longest-lasting effect came from writing down three things you were grateful for each day. Participants were only asked to do it for a week, but many kept their journals long after the study ended.

The new review adds two twists. First, the effect varied a lot from country to country, so a practice that helps in one culture may do little in another. Second, combining several kinds of gratitude exercise worked better than doing just one. And while grateful people do tend to be happier and less stressed, that link alone doesn't prove the journal caused it. A small effect isn't nothing, though: many researchers argue that small effects can add up over time.