rationalskepticism.org

In addition, it should again be emphasized: The finding is not the religious belief predicts greater longetivity. The finding is only that church attendance, specifically, does so. If you follow a religion but don't go to church regularly, there is no benefit. Obviously, this could be correlated with any number of confounding factors that might explain the association. The investigators did a pretty good job of trying to control for these, as far as I can tell (eg. they ensured that it wasn't simply that people who are in good health are more likely to get out of the house frequently). But it's impossible to control for everything. The major missing factor is trying to identify a secular equivalent to church that could serve as a comparison.

Another thing: The health benefits of a secular society may well affect all citizens alike, even the religious ones. So there is no reason that church attendance, or even religious belief, could not simultaneously have an independent effect on longetivity at an individual level.