Is there a link between faith and health? There have been over 1200 studies addressing this problem and 400 reviews. 81% of the papers showed a health benefit and 4% harm. For example an American study followed 21,204 Americans over 9 years, correlating various sociological data with death rates. Strangely, income and education were not independent prognostic factors, but those who attended church regularly had a life expectancy 7 years longer than those who did not. For black Americans the difference was 14 years (Hummer at al, Demography 1999; 36:273-85.)
Of course there are good reasons why church going might be conducive to longevity: fewer divorces, less alcohol and drug abuse, less cigarette smoking, less likely to be involved in violence and so on. But is there more than this?
Religion is often seen as a refuge for the weak-minded, but on the contrary churchgoers are more likely to cope well with mental illness. Religious involvement is correlated with well-being, happiness and life satisfaction; hope and optimism; purpose and meaning in life; higher self esteem; better adaptation to bereavement; greater social support and less loneliness; lower rates of depression and faster recovery from depression; lower rates of suicide and fewer positive attitudes towards suicide; less anxiety; less psychosis and fewer psychotic tendencies; lower rates of alcohol and drug abuse; less delinquency and criminal activity and greater marital stability and satisfaction. (Koenig et al. Handbook of Religion and Health. OUP 2001)
There have been reports of harm, particularly relating to extreme sects failing to take advantage of modern medicine, such as the Amish refusing vaccination or Jehovah's Witnesses refusing blood transfusion or Christian Scientists avoiding medical care, but these are rare.
Christians should not promote health benefits as the primary reason for coming to faith in Christ. Jesus came into the world to work a far deeper transformation of human lives than merely curing disease. Early Christians had a very high mortality, in fact, and Christians in many atheistic and Muslim countries experience the same today.