Any reader knows the unique delight of settling down with a good book.

But over the past two decades, there has been a steady decline in Americans who read for fun, according to a study published on Wednesday.

Researchers from University College London and the University of Florida examined national data from 2003 to 2023 and found that the share of people who reported reading for pleasure on a given day fell to 16 percent in 2023 from a peak of 28 percent in 2004 — a drop of about 40 percent. It declined around 3 percent each year over those two decades.

There is evidence that reading for pleasure has been declining since the 1940s, the researchers said, but they called the size of the latest decrease “surprising,” given that the study defined reading broadly, encompassing books, magazines and newspapers in print, electronic or audio form.

Many previous studies’ results could be questioned because they didn’t explicitly account for e-books and audiobooks, said Daisy Fancourt, a co-author of the study and a professor of psychobiology and epidemiology at University College London.

The study did not answer the question of why Americans were reading less. But the authors suggested some possible explanations, including increased use of social media and other technology, or more time spent at work because of economic pressure. Further research would be needed to confirm those theories.

The decline in reading could have implications for Americans’ learning, relationships and overall well-being, the researchers said.