Healthy young men who watch television for more than 20 hours a week have around half the sperm count of men who watch very little TV, say Harvard researchers in the British Journal of Sports Medicine.
Previous fertility studies suggest that semen quality has deteriorated over the past few decades, but no specific cause has been identified. To find out if a sedentary lifestyle might be a contributory factor, the Harvard team analyzed the semen quality of 189 American men between the ages of 18 and 22.
The men were asked about the quantity and intensity of weekly exercise they had had over the preceding three months, and how much time they spent watching television, DVDs, or videos over the same period. Factors that might affect sperm quality, including medical or reproductive health problems, diet, stress levels, and smoking, were also factored in.
Amongst the participants, the amount of moderate to vigorous physical activity taken every week ranged from 5 to 14 hours, while weekly TV screen time varied from 4 to 20 hours.
The analysis showed that those who were the most physically active – more than 15 hours a week – had a 73 percent higher sperm count than the least physically active.
Interestingly, the results showed that light physical exercise made no difference to the sperm count, no matter how frequent it was. But TV viewing had the opposite effect. Those who watched the most – 20 or more hours a week – had a sperm count that was 44 percent lower than those who watched the least.
“We know very little about how lifestyle may impact semen quality and male fertility in general so identifying two potentially modifiable factors that appear to have such a big impact on sperm counts is truly exciting,” said the study’s lead author, Audrey Gaskins (pictured).
Gaskins cautions that a reduced sperm count does not necessarily curb a man’s chances of being able to father a child, but the findings do suggest that a more physically active lifestyle may improve semen quality. She noted that other fertility indicators such as sperm motility, shape, and sample volume, were not affected by either TV viewing or exercise.
The type of exercise might also be important, Gaskins suggests. “Future studies should also evaluate the extent to which different exercise types affect semen quality as previous studies suggest that there might be opposing effects of different types of activity on semen characteristics.”