Healthy young men who watch TV for more than 20 hours a week have almost half the sperm count of men who watch very little TV, indicates a study published online in the British Journal of Sports Medicine.
Conversely, men who do 15 or more hours of moderate to vigorous exercise every week have sperm counts that are 73% higher than those who exercise little, the findings show.
Semen quality seems to have deteriorated over the past few decades, although it's not clear why, say the authors.