When psychology became important in medical treatment, doctors began to see connections between the mind and the body as causal. We are one organism: What affects the mind also affects the body. Now doctors are exploring the connections of the spirit to the mind and the body. Is it really true? We are one organism and what affects one part of us, may presently cause changes in another area.
It is easy enough to find out if certain beliefs cause a difference in a religious population rates of illness or mortality. Do fewer spiritual people get cancer from smoking than non-religious people? If so, the fact that many of them believe smoking to be a sin and refrain from it may explain how their religion protected them.
Another confounding factor may be definitions. Religious does not necessarily mean spiritual, at least, not to all people. A great many people are religious but do not seek inner peace or understanding--it is a difficult difference to explain. Who knows what happens in a person's spirit unless she can tell you; then it becomes a matter of mental ability to describe or understand.
I have found that spirituality goes beyond obedience to the commandments and supersedes sin--Spirituality is a plane of communication with God. I like to read some of the writing of Brother Lawrence. He talked about "practicing the presence of God." In the matter of illness, we have to consider that God may allow us to suffer pain due to the illness, but it doesn't mean he isn't beside or in us as we go through that experience.
When I am experiencing pain, I may look at my current activity. Is there something God is showing me about what I am doing? Is it something I should rest from? Not that the activity itself is wrong, but it's just that at that moment God will show me something else he wants me to see. I have lately begun to have pain in my neck when I sit in church. The pain seems to result from the fixed position. Maybe it's just that sometimes my neck hurts, and it's not spiritual. It's something to do with my neck. Maybe I just need to address it with the doctor. Maybe God will bless that, too.