With Medicine, Religion, and Health (Templeton Foundation Press, 2008), Harold Koenig makes a valuable contribution to understanding the relationship between religion, spirituality, and health for both practitioners and the general public. Koenig is a physician currently on the faculty at Duke University Medical Center and also the co-director of Duke’s Center for Spirituality, Theology, and Health. This field of religion, spirituality, and health, he informs us early on, is new and controversial. This direct statement lets the reader know from the start that the work is situated in an emerging field where findings are contested and conclusions tentative.

Koenig’s stated purpose is “to explore and make sense of some of the recent research on religion, spirituality and health” (7).  But the book is not just a survey.  It has a clear agenda, and it is infused with a sense of crisis and mission.  Two realities fuel the passion that drives Koenig’s argument.  First, the medical profession does not address patients’ spiritual and religious needs, even though studies demonstrate that spiritual support is one of the strongest factors influencing quality of life.  Second, an aging population, greater longevity, and projected $43 trillion debt in Medicare costs by the year 2040 forecast an impending health care crisis.  Having raised the reader’s anxiety and alarm, Koenig argues that religion and spirituality affects health positively according to research, and integrating religious and spiritual needs into medical care can contribute to addressing the coming crisis.

Koenig offers a nuanced approach to defining religion and spirituality that takes into account the reality that research and clinical contexts warrant different uses.  He defines religion as “a system of beliefs and practices observed by a community, supported by rituals that acknowledge, worship, communicate with, or approach the Sacred, the Divine, God (in Western cultures), or Ultimate Truth, Reality, or nirvana (in Eastern cultures) (11).”  He does not give as concise a definition of spirituality.  He argues that for research purposes spirituality has to be defined as a personal relationship that is connected in some way with the supernatural and/or traditional and nontraditional religion (17).  Spirituality cannot be conflated with positive psychological states, such as sense of meaning and feelings of love and awe, which are consequences of lived spirituality.  Beliefs, practices, and experiences that lack a connection with the supernatural or religion should fall under the category of humanism.  Koenig asserts that these distinctions give the word spirituality the specificity and clarity needed for research, where the aim is “to identify exact causes of better health and medical outcomes” (20). For clinical purposes, the definition can be much broader to include religious and nonreligious types and patient self-description (20).  In the flow of the text, Koenig often uses the term ‘religion’ to include both religion and spirituality (The rest of this review will follow this practice).

After defining the terms, Koenig builds a two-tiered model for positing a causal connection between religion and physical health.  First, he draws on research studies to show how emotions, social support, and behavior significantly affect physical health.  For example, chronic stress and anxiety can increase blood protein levels that weaken the immune system.  Second, he follows by examining how religious involvement impacts these factors and physical health through them.  For instance, he cites studies of how religious involvement is related to positive relationships that provide patients with greater life satisfaction.  In another example, he examines how religious involvement decreases the likelihood of heavy alcohol use and sexual promiscuity, both of which have demonstrated health consequences.  The causal connection between religion and health is mediated through these “pathways that are psychological, social, and behavioral” (37).  Accordingly, Koenig’s model highlights the way religion functions as a personal coping strategy, source of social support, and method of behavioral control (54).

Subsequent chapters in the book examine studies on various areas of health such as mental health; immune and endocrine systems; cardiovascular systems; diseases related to stress and behavior; longevity; and physical disability.  The numerous research findings presented are compelling.  Religious involvement, including service attendance and prayer, has strong correlations with decreased rates of major depression, less cardiovascular disease, and faster remission from certain conditions.  The challenge for those who want to take these findings as proof that religion causes good health is that they are mostly from epidemiological studies.

Here Koenig faces the most serious objection to his line of argument.  Observational studies, specifically cross-sectional studies, can demonstrate that identified factors are associated with a disease or rate of remission and they provide a weak basis for inferring causation.   As Koenig makes clear, there is always the possibility in such studies that characteristics not measured and controlled for could explain the relationship between religion and medical conditions (73).  Such factors are called ‘confounders’, because they create a false impression of association between religion and health outcomes (130).  An example would be unmeasured genetic factors that could influence rates of depression, or personality factors that make religious people more socially connected.  Koenig also cites the criticism that only randomized controlled trials (RCTs) can prove causation.  In RCTs, “subjects are randomized either to a religious intervention or a control group, and social support, mental health, and health behavior outcomes are measured over time” (132).  Through this method, RCTs can isolate and identify the exact characteristic that determines the outcome.

Koenig acknowledges the limitations of the cross-sectional studies, but makes three counter points.  First, he distinguishes confounding from explanatory variables.  Explanatory variables are the psychological, social, and behavioral factors through which religion influences physical health.  They help explain how religion affects health (131).  If the relationship between religious behavior and targeted health outcomes persist after confounders are controlled for, one can establish an actual relationship between them.  Koenig contends that critics make the mistake of conflating the two types of variables and fail to measure explanatory ones.  Second, he asserts that the amount of epidemiological evidence for religion’s role in increased future social support, faster recovery from depression, and reduction in harmful behavior “come very close to establishing causation” (132).  In addition to cross-sectional studies, the evidence pool includes many longitudinal studies that offer stronger grounds for inferring causation.  Third, some RCTs that have been conducted, specifically on depression and anxiety, do demonstrate a positive relationship between religion and health.

The final chapter on “Clinical Application” lays out clearly why, how, and when to assess and address patients’ spiritual needs.  The proposals for screening patients’ spiritual history, praying with patients, and working with chaplains and faith communities balance professional boundaries and practical integration of religious needs in the clinical context.  Each proposal appears practically feasible and accessible to health professionals.

Another helpful feature of the book is the “Further Resources” section, which is an extensive annotated list of key research studies.  It also includes lists of research reviews and multimedia resources that will be useful for practitioners and interested readers.

Medicine, Religion, and Health is a fair and well-argued work.  It does, however, have some areas that need more clarification. First, as James Rusthoven has pointed out (Rusthoven 2009), Koenig could strengthen his argument by exercising greater rigor in explaining the criteria used for choosing the studies.  The book is not designed to be a survey (for that readers can read Handbook of Religion and Health, which Koenig co-authored), and Koenig’s criteria of selection remains implied.  On a related point, Koenig’s assessments of the quality of the studies are more ad hoc than systematic, although he is very fair in pointing out weaknesses in the studies.

Second, it is not clear how closely his definition of spirituality and religion matches the definitions used in the research studies.  The reader assumes that they are at least compatible, and in many cases he outlines the definitions employed by the researchers.  Making explicit how the definitions line up and pointing out any important differences would give his argument greater clarity.

Third, Koenig notes but does not discuss what difference the specific type of religious practice makes in affecting health outcomes.  The point deserves attention because some studies indicate a weak relationship between private religious practice and health outcomes, while others indicate a stronger one.  How important a variable is the specific content of religious practice, and should future studies examine this aspect more carefully?

The most problematic issues that remain for Koenig’s argument are that the relationship between religion and physical health is twice removed, mediated through other factors, and that observational studies cannot prove causation.  Furthermore, where Koenig addresses negative effects of religion on health, the examples are few and his analysis insubstantial.  Despite these weaknesses, Koenig finds support for his argument from an impressive number of research findings.  His honesty and fairness in engaging criticisms and admitting shortcomings further strengthen his work.  Overall, Koenig makes a convincing case for taking seriously religion’s positive effect on health.  But there is more to the appeal of his book.  Medicine, Religion, and Health is a call to action.  If Koenig is right about the state of the health care system and the difference that religion and spirituality can make, the stakes are high.  The scientific inquiry into religion, spirituality, and health takes on economic and moral urgency.  Although the nature of the relationship between health and religion remains fiercely contested, Koenig’s work gives an important perspective on the field and deserves to be read widely.