From the blog post:

> Interestingly, those who felt the greatest boost in mood also experienced the biggest drop in heart rate variability.

A drop in HRV isn't generally good. So I check the paper, and found this:

> No significant changes were found in heart rate variability or resting heart rate over the course of the study in either of the groups (Figures 4C and 4D)

There was a reduction respiratory rate for those an increase in daily positive affect. Bottom line, unclear if this particular study points to a positive health outcome other than feeling happier.