The study, which was led by researchers from the Harvard School of Public Health, also found a positive association between sperm concentrations and physical activity.
“Our findings suggest that a more physically active lifestyle may improve semen quality,” the study’s authors conclude.
There’s been much debate in recent years about whether sperm counts have been on the decline. As the authors of this current study point out in their paper’s background discussion, the findings on sperm count trends have been inconsistent, although most data support a decline in Western countries. The causes of this observed decline have also been intensely debated, but decreases in physical activity and increases in sedentary behavior are often pointed to as likely culprits.
The new study recruited 189 male students from the University of Rochester in upstate New York. They were aged 18 to 22 years, with a median age of 19.6 years. Most were white (81 percent), had a normal body mass index (58.4 percent) and were non-smokers (77.4 percent). The students filled out questionnaires about their TV and exercise habits over the previous three months and provided a semen specimen during a clinic visit.
The questionnaires revealed that the young men spent a median of 8.25 hours per week engaged in moderate-to-vigorous physical activity and a median of 14 hours per week watching television. Based on the questionnaires, the researchers divided the students into four groups for both TV viewing and physical activity. They then compared the students’ sperm concentrations to where the young men fell in those quartiles.
The analysis found that the students in the group that watched the most TV (20 or more hours per week) had sperm counts that were, on average, 44 percent lower than the students who reported spending no time in front of the TV.
It also found that the students who were the most physically active (14 or more hours of exercise per week) has sperm counts that were, on average, 73 percent higher than those who were the least physically active (less than 5 hours of exercise per week).
Overall, those students with both the highest TV watching and the lowest physical activity had the lowest sperm concentrations, on average.
It’s important to point out that none of the young men’s sperm count was what could be called sub-fertile, and that neither TV viewing nor physical activity had any effect on sperm motility (its ability to “swim”).
Reasons for findings unclear
The findings suggest that “lifestyle changes such as increases in physical activity may positively influence sperm count and concentration in reproductive-aged men,” according to the study’s authors.
But men shouldn’t overdo it. Other studies have found that too much exercise, especially bike riding and long-distance running, can lower sperm concentrations.
Why being a couch potato would be associated with a lower sperm count isn’t entirely clear. It may be that sitting for long periods causes the scrotom to get too warm. Higher scrotal temperatures have been found in other research to be associated with lower sperm production. But whether those higher temperatures are the cause or the consequence of poor sperm production is another area of intense debate.
The authors of this new study point out that their findings are preliminary. The study comes with several caveats: It had a relatively small number of participants; it relied on self-reporting of TV and exercise habits (self reports can be inaccurate); and it used only a single sperm sample from each student for its analysis.
In other words, stay tuned.