Men who watch television for 20 hours per week have almost half the sperm count of those who watch very little television or none at all, a new study has found.
US researchers recruited 189 young men aged between 18 to 22, questioned them about their exercise, diet and TV habits and asked them to provide a sperm sample.
Men in the top quarter of TV-watchers — those who watched for 20 hours or more — had a 44-per cent lower sperm count than those who watched least, meaning they said they watched "none or almost none."
Another big factor was exercise, according to the study, published online in the British Journal of Sports Medicine.
Men who exercised for 15 or more hours weekly at a "moderate to vigorous" rate had a 73-per cent higher sperm count than those who exercised less than five hours per week.
None of the sperm levels was so low that the man would have been unable to father a child.
Semen quality appears to have declined over several decades, according to studies conducted in several countries.
It is unclear why this has happened but scientists suspect that sedentary lifestyles may warm the scrotum and affect semen concentrations. Physical inactivity has also been linked to increased levels of oxidative stress, in which rogue oxygen compounds degrade cells.
Previous studies into physical activity and semen quality have focused on elite athletes, such as professional marathon runners and cyclists.
"We were able to examine a range of physical activity that is more relevant to men in the general population," study co-author Jorge Charravo, assistant professor of nutrition and epidemiology at Harvard School of Public Health in Boston tells AFP.
The study was limited by the relatively small number of volunteers and the fact that only a single sperm sample was provided, the authors acknowledge.
Merits of moderate exercise
While the study was small, it was well designed and attempted to control for variables such as diet, body mass index and smoking that might differ between the two groups of me, says Dr. Allan Pacey, senior lecturer in andrology at the University of Sheffield.
"I would agree that there is evidence to suggest that moderate exercise could change men's physiology sufficiently to improve testicular health," says Pacey, who was not involved in the study.
"However, it remains to be seen if coaxing a TV watching couch potato into doing some regular exercise could actually improve his sperm count. Or whether there exists an unknown fundamental difference between men who like exercise and those who do not," he says.
But before worried men grab their sportsbag, he urges caution.
"It's important to note that other research suggests that doing too much exercise can be harmful to sperm production and this study did not examine the type and intensity of exercise their participants were undertaking.
"My advice would be everything in moderation — and that includes time in the gym as well as watching TV (or perhaps both at the same time!)"
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