Those watching 20-plus hours of TV a week had sperm counts 44 percent lower than those who watched very little, the study found. That could be because the lack of activity was bad for health, or because being regularly stuck to the couch raised temperature in the scrotum, which can hurt semen production, said Chavarro.
The researchers didn't break down semen quantity by participation in different types of sports, though they may do so in future research.
The good news for TV watchers was the study found little correlation between amounts of exercise or TV viewing volume with sperm quality, meaning that their sperm weren't deformed and could move in the right way.
The study was funded by the National Institutes of Health and the European Union's Developmental Effects of Environment on Reproduction project.