Researchers at the Harvard School of Public Health examined the semen quality of 189 college men between the ages of 18 to 22 during 2009 and 2010. They also asked the men about their TV viewing habits, including questions about their exercise, diet, stress and smoking habits – factors that can impact sperm quality.
The study found that men who watched more than 20 hours of TV shows weekly had a 44 percent lower sperm count versus those who rarely to never watched television.
The study also found lower sperm counts in men who don't exercise regularly, which may alleviate the concerns of active men who may have previously heard that exercise could decrease sperm counts, says study co-author Jorge Chavarro, an assistant professor at the Harvard School of Public Health.
"Most of the previous research has focused on endurance athletes, such as marathon runners and professional cyclists," whose bodies may be under unusual stress, said Chavarro, adding that bikers are especially at risk because their scrotums can become injured or overheated during long rides on a bicycle seat.
However, for the average active male who isn't a professional athlete, the Harvard study found that the men who exercised the most (more than 15 hours a week) had sperm counts that were 73% higher than those who exercised the least (less than five hours a week).
Chavarro also said that 25 percent of the 189 men in the study reported watching more than 20 hours of TV per week.
Other studies have shown that obesity and high-fat diets also contribute to lower sperm counts, but even when weight and diet were factored into the new study, Chavarro says the links between TV, exercise and sperm counts held up. He and his co-authors suggest that metabolic changes related to inactivity, and heating of the scrotum caused by prolonged sitting in front of the TV, might also contribute to lower sperm counts.