Twenty-plus hours per week? Who has so much free time they can devote such a fat chunk of their lives to clicker-clutching couch vegging? Apparently, many of us, said Jorge Chavarro, senior author of the study and assistant professor of nutrition and epidemiology at Harvard.

“It’s not difficult to imagine. That’s about three hours a day,” Chavarro said. “Let’s say somebody comes home from work at 7 and turns on the TV; they only need to watch TV until the evening news and they’ve watched three hours.”

Starting in the 1990s, studies have suggested a reduction in sperm counts among men in various cities, including in Europe and the United States. It’s become more clear in the past six years.

“Most people have speculated these are due to higher use of environmental chemicals,” Chavarro said.

“One of the things that has been overlooked during same six-year period: there also have been vast changes in how people live their lives, including how people eat, watch television, move around – whether they are active or not. Relatively little attention has been paid to these factors (when it comes to sperm counts). We wanted to look at that.”

Researchers, whose report appeared in The American Journal of Clinical Nutrition, found that young Danish men who ate the most saturated fats had a 38 percent lower concentration of sperm, and 41 percent lower sperm counts in their semen, than those who ate the least fat.

“We cannot say that it has a causal effect, but I think other studies have shown that saturated fat intake has shown a connection to other problems and now also for sperm count,” said Tina Jensen, the study’s lead author from Rigshospitalet in Copenhagen, the Danish capital.

The research is not the first to connect diet and other lifestyle factors to sperm production and quality. In 2011, Brazilian researchers found that men who ate more fruit and grains suchs wheat, oats or barley had faster and more agile sperm, as well as more sperm overall.

But that study and most others looked at these associations using data on men seeking fertility treatments, which may not be representative of all men.