This question can be asked in two different ways. One can ask whether religious people live longer than their non religious compatriots, or one can ask whether people living in religious countries enjoy longer lives than people in secular countries. Oddly, the answers to these questions are very different.
Countries with very low life expectancy are mostly very religious. The nations of sub-Saharan Africa are a good example. Plagues of malaria, parasites, dengue fever, cholera, diarrheal diseases, HIV/AIDS, etc., lop decades off life expectancy that is below 60 years for most of these countries. The presence of many serious chronic illnesses, and the expectation of an early death, predicts universal belief in God and the importance of religion (1).
With economic development, health improves, but religion declines (1). This means that developed countries are both healthier and more secular. Developed countries reap the benefits of improved healthcare, sanitation, and public health programs such as vaccination for measles and smallpox. As a result, average life expectancy has literally doubled from what it was a century ago.
So secular populations definitely live much longer than residents of highly religious countries. Examples include Sweden (life expectancy of 81 years) and Japan (life expectancy of 82 years) where residents outlive more religious Americans (78.5 years). Now, what happens if one compares religious and secular people in the same country?
Comparing religious and non religious in the same country
That depends on which country one studies. Much of the relevant research was conducted in the U.S. where larger advantages in longevity were reported for religious people in some studies, but little or no advantage was found in others. It is difficult to make sense of these discrepancies but it seems likely that religiously observant people in the U.S. live longer than those who stay away from church.
Religious Americans are reported to have more robust immune systems, lower blood pressure, and better recovery times from operations, (although these claims have been disputed) (2, 3). Attending church provides many potential health advantages including promotion of a healthier lifestyle, improved stress management, and better social support (4). Such benefits could explain why religious Americans live longer according to some studies.
Yet, the apparent health benefits of religion are not found in some other developed countries. In states like Denmark and the Netherlands, where religiously active individuals are in the minority, any health advantages of religion shrink to vanishing point as illustrated by research on clinical depression (5). (Depression is strongly related to heart disease and hence to mortality.)
What does it all mean?
When we compare people living in the same country, religious people enjoy a health advantage if they are part of a large majority, as is true of the U.S. That advantage disappears if religious people are in the minority.
Why? One plausible reason that non religious people in the U.S. have worse health is that they are largely excluded from participation in politics, and find that they have less of a role to play in their local communities because religious people consider them unworthy. One key reason for this is that churches play a central role in organizing charities and civic organizations.
In predominantly secular countries, community involvement is very high (6) so that atheists are much more active in their communities than they would be in a comparatively religious country such as the U.S. Instead of feeling like second class citizens, the non religious are fully integrated in their communities with all of the health advantages this brings. So what had looked like advantages of religion could be simply an advantage of being in the mainstream.
In the U.S. some health researchers are fond of giving religion the credit for boosting life expectancy. Yet despite being a nation with a large religious majority, Americans have much lower life expectancy than is enjoyed by secular countries at a similar level of economic development such as Japan and Sweden. Evidently, the lower quality of life here both provides a market for religion and reduces life expectancy.
From that perspective, it seems bizarre that health researchers would be so keen to tout the alleged health advantages of religion (2). If religion really promoted longevity, how could people have such short life expectancy in sub-Saharan Africa where virtually everyone is deeply religious?
1. Barber, N. (2012). Why atheism will replace religion: The triumph of earthly pleasures over pie in the sky. E-book, available at: http://www.amazon.com/Atheism-Will-Replace-Religion-ebook/dp/B008...
2. Koenig, H. G. (2008). Medicine, religion and health: Where science and spirituality meet. West Conshohocken, PA: Templeton Foundation Press.
3. Sloan, R. P., and Bagiella, E. (2002). Claims about religious involvement and health outcomes. Annals of Behavioral Medicine, 24, 14-21.
4. Paul-Labrador, M. D. et al. (2006). Effects of a randomized controlled trial of transcendental meditation on components of the metabolic syndrome in subjects with coronary heart disease. Archives of Internal Medicine, 166: 1218-1224.
5. Snoep, L. (2008). Religiousness and happiness in three nations. Journal of Happiness Studies, 9, 207-211.
6. Zuckerman, P. (2008). Society without God: What the least religious nations can tell us about contentment. New York: New York University Press.