This paper provides a concise but comprehensive review of research on religion/spirituality (R/S) and both mental health and physical health. It is based on a systematic review of original data-based quantitative research published in peer-reviewed journals between 1872 and 2010, including a few seminal articles published since 2010. First, I provide a brief historical background to set the stage. Then I review research on R/S and mental health, examining relationships with both positive and negative mental health outcomes, where positive outcomes include well-being, happiness, hope, optimism, and gratefulness, and negative outcomes involve depression, suicide, anxiety, psychosis, substance abuse, delinquency/crime, marital instability, and personality traits (positive and negative). I then explain how and why R/S might influence mental health. Next, I review research on R/S and health behaviors such as physical activity, cigarette smoking, diet, and sexual practices, followed by a review of relationships between R/S and heart disease, hypertension, cerebrovascular disease, Alzheimer's disease and dementia, immune functions, endocrine functions, cancer, overall mortality, physical disability, pain, and somatic symptoms. I then present a theoretical model explaining how R/S might influence physical health. Finally, I discuss what health professionals should do in light of these research findings and make recommendations in this regard.

Religious and spiritual factors are increasingly being examined in psychiatric research. Religious beliefs and practices have long been linked to hysteria, neurosis, and psychotic delusions. However, recent studies have identified another side of religion that may serve as a psychological and social resource for coping with stress. After defining the terms religion and spirituality, this paper reviews research on the relation between religion and (or) spirituality, and mental health, focusing on depression, suicide, anxiety, psychosis, and substance abuse. The results of an earlier systematic review are discussed, and more recent studies in the United States, Canada, Europe, and other countries are described. While religious beliefs and practices can represent powerful sources of comfort, hope, and meaning, they are often intricately entangled with neurotic and psychotic disorders, sometimes making it difficult to determine whether they are a resource or a liability.

There is need for a brief measure of religiosity that can be included in epidemiological surveys to examine relationships between religion and health outcomes. The Duke University Religion Index (DUREL) is a five-item measure of religious involvement, and was developed for use in large cross-sectional and longitudinal observational studies. The instrument assesses the three major dimensions of religiosity that were identified during a consensus meeting sponsored by the National Institute on Aging. Those three dimensions are organizational religious activity, non-organizational religious activity, and intrinsic religiosity (or subjective religiosity). The DUREL measures each of these dimensions by a separate “subscale”, and correlations with health outcomes should be analyzed by subscale in separate models. The overall scale has high test-retest reliability (intra-class correlation = 0.91), high internal consistence (Cronbach’s alpha’s = 0.78–0.91), high convergent validity with other measures of religiosity (r’s = 0.71–0.86), and the factor structure of the DUREL has now been demonstrated and confirmed in separate samples by other independent investigative teams. The DUREL has been used in over 100 published studies conducted throughout the world and is available in 10 languages.

Spirituality is increasingly being examined as a construct related to mental and physical health. The definition of spirituality, however, has been changing. Traditionally, spirituality was used to describe the deeply religious person, but it has now expanded to include the superficially religious person, the religious seeker, the seeker of well-being and happiness, and the completely secular person. Instruments used to measure spirituality reflect this trend. These measures are heavily contaminated with questions assessing positive character traits or mental health: optimism, forgiveness, gratitude, meaning and purpose in life, peacefulness, harmony, and general well-being. Spirituality, measured by indicators of good mental health, is found to be correlated with good mental health. This research has been reported in some of the world's top medical journals. Such associations are meaningless and tautological. Either spirituality should be defined and measured in traditional terms as a unique, uncontaminated construct, or it should be eliminated from use in academic research.