Increased life expectancy is leading to people "putting off" becoming involved in religion, UK researchers have said.
Their International Journal of Social Economics paper suggests decisions about "religiosity" depend on perceived social and spiritual benefits.
As people live longer, younger people are less concerned about what happens after death.
The researchers say religion must do more to emphasise the social benefits to the young in order to attract them.
Church attendance in the UK has been dwindling during the past 50 years.
And while 26% of over-65s attend church, only 11% of those aged between 16 and 44 do so.
However, in countries including many in sub-Saharan African and Latin American nations, religious adherence remains strong.
The study, by University of East Anglia and University of St Andrews researchers, analyses religiosity using a cost-benefit economic model.
It had previously been thought that the different patterns of "religiosity" seen around the world were due to economic factors - with poorer communities attending more, and government attitudes to religion.
The paper considers religion as a whole, but it says the Church of England is the prime example of the problem.
But Dr Elissaios Papyrakis, of the University of East Anglia, said the analysis suggested life expectancy was key to people's views.
He said that in poorer countries where life expectancy remains low, a larger share of the population, both young and old, was concerned about what happens after death, naturally encouraging religious participation.
"Many religions and societies link to some degree the cumulative amount of religious effort to benefits in the afterlife," he said.
"We show that higher life expectancy discounts expected benefits in the afterlife and is therefore likely to lead to postponement of religiosity, without necessarily jeopardising benefits in the afterlife.
He added: "The findings have important policy implications for what churches want to do and how they attract members.
Dr Papyrakis said religious organisations should be prepared to accept and attract a "greying church", with membership skewed towards the older generation, particularly in countries like the UK where life expectancy is high.
Because of this, he suggested more immediate benefits should be promoted by religions.
"It is important to emphasise socio-economic and spiritual benefits that can be enjoyed during one's lifetime on Earth, for example expanding a person's social circle, communal activities, spiritual fulfilment, support and guidance, rather than uncertain rewards in the afterlife.
"These benefits can counterbalance the negative impact of life expectancy on religiosity - which in effect reduces concern about life after death - and therefore encourage religious involvement."
However, a spokesman for the Church of England disputed the idea that people became part of an organised religion after assessing potential "benefits".
"People go to church because they believe in something and wish to join in with a community of people who think they same way."
He added: "The theory doesn't fit with the US, which has the highest church-going figures in the world.