Weekly church attendance has waned among U.S. Catholics in the past decade, while it has remained steady among Protestants, a new survey from Gallup has shown.

From 2014 to 2017, an average of 39 percent of American Catholics reported attending church in the past seven days.

This is down from an average of 45 percent from 2005 to 2008 and represents a steep decline from 75 percent in 1955, said Gallup.

In 2009, Gallup had reported the steepest decline in church attendance among U.S. Catholics occurred between the 1950s and 1970s, when the percentage saying they had attended church in the past seven days fell by more than 20 percentage points.

Through the mid-1990s before stabilizing in the mid-2000s, it then fell an average of four points a decade.

"Since then, the downward trend has resumed, with the percentage attending in the past week falling another six points in the past decade," said Gallup.

Back in 1955, practicing Catholics of all age groups would largely observe their weekly mass obligation.

At that time, roughly three quarters of Catholics, regardless of their age, said they had attended church in the past week.

This had begun to change in the 1960s, however, as young Catholics became gradually less likely to attend.

The decline accelerated through the 1970s and has since continued at a slower pace.

In the 1950s U.S. Protestants' church attendance was not nearly as high as Catholics', but it has not diminished over time.

Protestants' church attendance dipped in the 1960s and 1970s among those aged 21 to 29, but it has since rebounded. Among those aged 60 and older, weekly attendance has grown by eight points since the 1950s.

PROTESTANTS' PIE SHRINKING FASTER THAN CATHOLICS'

While drawing parishioners to weekly services is essential for both Catholics and Protestants alike, so too is maintaining a large base of Americans identifying with each faith group.

Although the rate at which Protestants attend church has stayed consistent over the past six decades, the percentage of Americans identifying as Protestant has declined sharply.

It has fallen from 71 percent in 1955 to 47 percent in the mid-2010s.

Since 1999, Gallup's definition of Protestants has included those using the generic term "Christian" as well as those calling themselves Protestant or naming a specific Protestant faith.

By contrast, while the Catholic Church has suffered declining U.S. attendance., the overall percentage of Catholics has held firm, largely due to the growth of the U.S. Hispanic population.

Twenty-two percent of U.S. adults today identify as Catholic, compared with 24 percent in 1955.

Gallup notes, however, that a troubling sign for both Catholics and Protestants is that younger adults, particularly those aged 21 to 29, are less likely than older adults to identify as belonging to either confession.

"This is partly because more young people identify as 'other' or with other non-Christian religions, but mostly because of the large proportion – 33 percent -- identifying with no religion," says Gallup.