Spirituality has always been associated with the quest for health. Camberwell in south London, I recently learned, derives its name from a healing well frequented by those who were "cambered", or physically disabled. But it is only a scientific age that would seek to distil causal links between a spiritual practice and its physical effects, and perhaps also be concerned to exorcise any metaphysical excess.

The discussion of the benefits of practices traditionally associated with religions is firmly on the secular agenda. The new edition of the Handbook of Religion and Health lists more than 3,000 published studies. Research on forgiveness and gratitude alone has increased by an order of magnitude since the turn of the millennium.

Robert Emmons, professor of psychology at University of California, Davis, has gathered evidence to show that gratitude has psychological benefits, sustains physical wellbeing and feeds human relationships. He also believes there is an important spiritual side to the virtue, as gratitude cultivates a sense of fulfilment in life by nurturing the sense of dependency on others and God.

Or consider forgiveness. A significant cultural reassessment of this virtue seems under way: it is now taken less as a sign of weakness and more of inner strength. "Genuine forgiveness is important in transforming relations, just as confession, apology and repentance are. Forgiveness is connected to other virtues, like empathy and justice," adds Charlotte vanOyen-Witvliet, professor of psychology at Hope College, Michigan. She is also keen to stress that forgiveness is not about forgetting the damage of the offence, but is interested in the wellbeing of the offender.

Researchers emphasise that the links between spirituality and wellbeing need much further study. "Do we really know what it is about what sort of religion, spirituality or belief that enhances health?" asks Stephen Post, author of The Hidden Gifts of Helping and moderator of a recent conference that addressed these issues, Spiritual Progress and Human Flourishing. His answer is no, but "progress is being made".

Teaching spirituality and health is also being promoted. In August, Oxford University Press published a textbook for public health professionals, The Oxford Textbook of Spirituality in Healthcare. Christina Puchalski of the George Washington Institute for Spirituality and Health, and one of the book's editors, argues that healthcare improvements have been driven by technology. "What is unfortunately missing is a relationship-centred compassionate approach," she argues, "and that's the foundation of spirituality in healthcare."

And the burgeoning interest raises theological questions too. Another book, published in September by the Templeton Press, asks whether healthcare risks turning faith into a medical commodity. Healing To All Their Flesh: Jewish and Christian Perspectives on Spirituality, Theology, and Health, worries that, while research on religion and health is now acceptable, it may be distorting. As Jeff Levin, one of the book's editors, writes in the prologue: "Religion is just more grist for the mill of structural-equation models, survival analyses, logistic regressions and the like."

In other words, there is a lack of theoretical and theological reflection in the field and that matters for two reasons. One is scientific. Levin continues: "A medical researcher would never conduct a study of the health impact of, say, environmental toxins or nutritional status or social support without first consulting an environmental toxicologist or a nutritionist or a sociologist who could expertly identify what questions to ask, what hypotheses to frame, and, once data were collected, how to analyse the data and then how to interpret findings. Yet, in studies of religion and health, this is done all the time; it is probably the norm. This is foolish, irresponsible and self-defeating."

Second, it matters at a human level. Could there be something cruel in "prescribing" a spiritual practice as if it were a pill because of the implications for the patient when the supposed "remedy" fails to work? What is not being asked is what religious traditions actually teach about the link between faith and health – a question that might then lead to others, like how the status of the spirit matters for the functioning of the body?

After all, it seems likely that the wellbeing gained from religious practices would be indirect. The believer who says grace at the start of a meal does not do so to be happy but to thank God. Alternatively, and reflecting on Julian Baggini's interesting article on atheists fasting, celebrating a newfound control of the appetites could confuse the means with the end: spiritually speaking, fasting is about expanding an individual's range of interests so that they can move beyond material concerns.

Spirituality and health are both great goods. But confusing the two brings risks. It might load individuals already anxious about their lifestyles with yet more burdens. And it could stymie the spiritual transformation of the person.