This NY Times article, Religion and Health: New Research Revives an Old Debate, does a decent job of presenting the pros and cons. This stood out for me:
Stronger evidence exists to suggest that religion is beneficial to mental health, he said. Because mental health is connected to physical health, he said, it stands to reason that religion would also be associated with physical health.
But what’s missing from the discussion is a differentiation between religious and spiritual activities. I’ve not given a lot of thought to this, but I tend to think of activities like volunteering at a soup kitchen, visiting the sick, and teaching Sunday School as religious activities when they’re done as part of one’s faith. Saying the rosary and walking a labyrinth are spiritual activities. Seems like the researchers should differentiate between the two.