How does religious service attendance and spirituality affect health outcomes? On August 26, 2016 Tyler VanderWeele, professor of epidemiology at Harvard T.H. Chan School of Public Health, answered questions about the topic during a Reddit “AMA (Ask Me Anything).” Vanderweele recently led a study that found that women who attended religious services more than once per week were more than 30% less likely to die during a 16-year-follow-up than women who never attended. He also co-authored a second study that found that women attending church services at least weekly were at five-fold lower risk for suicide, with an even larger effect for Catholics. Below are some highlights from the AMA:

Are there any alternatives to religion that you believe would result in similar effects, for example other types of community involvement or activities such as meditation?

That is a good question: To what extent would this hold for other forms of social participation? There is certainly evidence that suggests that other forms of community involvement has an effect on health as well, though the size of the effect tends to be somewhat smaller than it is for service attendance. When we looked at religious service attendance itself, our analyses indicated that social support explains only about a quarter of the effect on longevity. Other mechanisms such as decreasing smoking, increasing optimism, and decreasing depression seemed important also. Meaning and purpose in life, and self-control, have also been suggested as other mechanisms but we did not have data on those in our data. Social support is thus important but it is not everything.

My speculation, though we do not yet have data on this, would be that groups that not only have social gatherings, but also have a shared sense of meaning, healthy behavioral norms, and a common vision for life would have a larger effect on mortality in follow-up than, say, merely showing up for a regular card game. Religious service attendance likely affects health not simply because of social support, but also because it potentially shapes so much of one’s outlook, behavior, beliefs, and one’s sense of life’s meaning and purpose.

I am less familiar with the literature on meditation. I know some of the research suggests an effect at least on positive psychological outcomes. I would be interested in studying this further.

With regard to social participation though, when we compared religious service attendance to other social measures, religious service attendance was the strongest predictor of subsequent mortality in follow-up. The protective association with mortality was fairly similar to being married and considerably stronger than the number of close friends, number of close relatives, having seen close relatives at least monthly, having seen close friends at least monthly, and number of hours spent in social group participation. Other forms of social participation certainly do matter and are beneficial but again the association with religious service attendance seems somewhat stronger.

How do you conclude causality? Would not people with chronic diseases, or who engage in activities such as smoking and heavy drinking be less likely to attend social circles disapproving of this, and thus resulting in a self-selected group giving the same statistical results for different reasons?

With data of this sort one generally cannot definitively demonstrate a cause-effect relationship, but one can provide evidence for it. We controlled for baseline behaviors like smoking and heavy drinking since it is indeed the case that those smoke or drink heavily are less likely to attend. But even controlling for the baseline behaviors, those who smoke or drink heavily and do still attend are more likely to subsequently cease smoking and drinking. The fact that we were able to control for so many of the potential common causes of service attendance and mortality helps strengthen the evidence.

Another difficult issue in addressing questions of causality is what is sometimes referred to as the possibility of “reverse causation,” i.e. the possibility that only those who are healthy can attend services, so that attendance isn’t necessarily influencing health. Some prior studies on the topic were criticized for this possibility. We tried to address these concerns. The only way to sort through these issues is to measure repeatedly, over time, both religious service attendance, health behaviors, and health itself and see which changes precede which others. That we had data on both service attendance and health repeatedly over time helps provide evidence about the direction of causality. Even when controlling for all of that, the analyses found that those who attended religious services regularly were about 30% less likely to become depressed, about 5-fold less likely to commit suicide, and about 30% less likely to die in the 16-year follow-up. We cannot be certain about causality, but we can provide evidence, and here the evidence seems quite strong.

What got you originally interested in these types of studies?

I have worked in public health and epidemiology for some time. The focus of much of my research is on the development of new statistical methods for assessing causation and for distinguishing association from causation. I also do a lot of work on assessing mechanisms with empirical data and statistical methods and have even written a book on the topic.

Religious faith has always been an important part of my life. Some years ago, I began to wonder if there was any literature on the intersection between my work in public health and topics of religion or faith. Much to my surprise there were hundreds of studies published on the topic. The associations between religious participation and health seemed to be pretty well established but two big open questions in the literature were: (i) is the relationship causal? and (ii) if so, what are the mechanisms? So it turned out that the open questions coincided exactly with the focus of my methodological work and I started looking for good datasets to carry out more rigorous analyses.

During my third year on faculty at Harvard a colleague pointed me to the Nurses Health Study data. He said he thought that there was a question on religious service attendance that no one had ever really used. Sure enough, it was there and it was measured repeatedly every four years. The perfect dataset was essentially waiting for me right here. The papers were the result of that work. We were able to provide pretty strong evidence for causality (again, one can generally not definitively prove causality with observational data, only provide varying strengths of evidence, as per my reply to wolfdoc) and we were also able to identify some of the important mechanisms such as social support, smoking, depression, and optimism. We will be looking at meaning and purpose in life and self-control as potential mechanisms using other data (as these were not in the Nurses’ Health Study dataset). So it ended up being a wonderful confluence of my interests, expertise, and the data that was available.

Check out the full AMA here.