The study looked at formal laughter therapy in postpartum women and found that those who engaged in the laughter therapy had significantly different levels of sIgA levels in breast milk. The authors conclude that laughter therapy can be applied as a complementary and alternative medicine intervention.
Comment: This study has a control group, but not a control treatment, so the Hawthorne Effect cannot be excluded as a cause for the differences found. However, the Hawthorne Effect is somewhat less likely in patients with a measurable change in sIgA. So, this study is hypothesis generating but not very good evidence that laughter therapy affects sIgA. It could be that simply socializing caused the difference in sIgA, or just getting out of the house; we just cannot conclude that the laughter therapy was the causative factor.
J Altern Complement Med. 2015 Dec;21(12):781-8