Interest in the connection between faith and health has led to a relatively large number of studies investigating the link. Some religious groups, including some actively involved in alternative medicine, claim to offer complete health to their adherents. Evaluating the health of believers in those religions would provide important evidence about the truth or falsity of those religions (as has been done for the First Church of Christ, Scientist, or Christian Scientists). For this reason, it is important to answer the question as to whether the Bible teaches that God promises to heal Christians. Does it?
More Information:
Scientific studies seem to support the idea that religion and faith are important factors in health. Numerous studies show a positive correlation between involvement in religious practices and  people’s health.
A large proportion of the published studies suggest that religious commitment may play a beneficial role in preventing mental and physical illness, improving how  people cope with mental and physical illness, and facilitating recovery from illness.
The foreword to a recent book summarizing the results of hundreds of these studies put it this way: “As those of us who have labored in this field for many years have long suspected, the relationship between religion and health, on average and at the population level, is overwhelmingly positive. Now we can say, finally, that we know this to be true.”
This conclusion is not held by all researchers.
Much still remains to be investigated with improved studies specially designed to investigate the connection between religious involvement and health status.
However, a better picture of the situation has emerged over the last several years. As would be expected, things are complicated. One review, which used only high-quality studies, arrived at some general conclusions.

• Frequent church attendance is strongly connected to increased life expectancy (by up to 25 percent).
• Viewing oneself as religious seems to be connected with having less heart disease, although not all studies confirmed this.
• Prayer improves recovery from some acute diseases, though again, only some of the evidence supports this claim.
• People who value religion consistently showed no benefit in recovering from acute diseases and in some cases were found to have slower recovery. Researchers have suggested that this may be due to patients’ struggling over why God had “abandoned them” in their illness, an issue I address in the next section.
• Religiosity failed to protect people against cancer, disability, or death.
• Benefits are greatest when religious faith is an important part of who that person is.
• Strong faith not only influences a person’s understanding of the meaning of life but also serves as a guide for living, motivating  people to avoid risky or unhealthy behavior.

A 2005 study provides a good example of the complexities of this research.
Chronic stress puts  people at higher risk for several diseases, including diabetes, heart disease, and cognitive disorders. A person’s long-term risk correlates well with measurements of blood pressure and of a hormone called “cortisol.” Higher levels of both correlate well with a higher level of chronic stress and a higher risk of disease.
When these levels were measured in university students, some interesting patterns were seen between the results and the students’ levels of religiosity and spirituality.
Students reporting themselves as religious to any extent had lower cortisol levels after receiving stressful stimuli compared to those who said they were “not at all religious.”
Closer examination of the students’ religiosity revealed that those with better cortisol scores prayed more frequently and rated themselves high in ability to forgive.
No significant correlations were found for attendance at religious ser vices, frequency of meditation, or use of religion to deal with stressful situations.
Blood pressure measurements actually revealed conflicting results. Men who were more religious had lower blood pressure, while more religious women had higher blood pressure. This finding differs from other studies in which, in general, higher religiosity correlates with lower blood pressure.
Other studies of the impact of religion on health also have not been uniformly positive. A small number of researchers found no correlation between faith and health, and in some cases they found a negative effect.
From a scientific perspective, some of these studies have significant limitations. Some were poorly designed and sometimes did not take into account the difficulty in measuring such factors as  people’s religiosity or spirituality.
Many used simple questions such as, “Do you attend church?” to measure  people’s religiosity.
In spite of these limitations, the studies seem to indicate that those who rarely attend religious services, or have little personal faith, are at higher risk for disease and illness, especially those connected with stress.
The general health benefits of faith are real — and the deeper and more internalized the faith, the greater the benefits.
Scientific research has demonstrated that much, even if it hasn’t (and probably can’t) prove why  people benefit from religious faith.
That also is a matter of faith.
Christians are Told to Expect Suffering

Although faith can improve our health, we should not assume that our lives can or will be trouble-free.
In fact, the Bible tells Christians to expect suffering and not to be surprised by suffering. “For it has been granted to you on behalf of Christ not only to believe on him, but also to suffer for him” (Philippians 1:29; see also 1 Thessalonians 3:4; 1 Peter 4:12).
We are to comfort one another and encourage one another with the knowledge that our destiny is secure in the arms of the Lord, even in the face of suffering and death (1 Thessalonians 4:13 – 5:11).
Some claim illness and suffering reflect weakness in an individual’s faith, but this is not borne out by the biblical record.
The New Testament mentions by name a number of early church leaders, people we can assume had strong faith, who got sick. All died.
Every faith healer in recorded history has gotten sick and died — some at a young age.
==================
You can read more on this topic in my book, Alternative Medicine: The Christian Handbook.
Also, citations to all of the studies quoted in this blog are found in the book.
==================
Additional Blogs on Faith-Based Health and Healing:

• Part 1 – What does the Bible say about health?
• Part 2 – What Value Should We Place on Our Health?
• Part 3 – Devout Faith Helps but Does Not Guarantee Good Health
• Part 4 – Can Faith be Unhealthy?
• Part 5 – What Causes Sickness?
• Part 6 – Why God’s Response Isn’t Always to Heal
• Part 7 – Not All Healing is From God
• Part 8 – Illegitimate Spiritual Practices
• Part 9 – Life Energy and Medical Magic
• Part 10 – Medical Characters Condemned for Pursuing Certain Forms of Healing
• Part 11 – Look to the Bible, Not Inner Voices, for Guidance
• Part 12 – Biblical Principles on Which to Base Medical Decisions and The Power of Faith