Physical activity is strongly associated with men's sperm quality according to a study looking into the effects of TV viewing and exercise. However, as the study was small and only looked at one point in time, it cannot give a definitive answer as to whether physical activity can improve sperm quality.
'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 lead author Audrey Gaskins, a doctoral student at the Harvard School of Public Health.
The study included 189 college students aged 18-22 years old and found that both sperm concentration and total sperm count were related to the time spent watching TV. The men who watched the most TV (more than 20 hours a week) had 44 percent lower sperm concentrations compared to men who didn't watch any TV. Although TV watching hadn't been studied before, another large study has found similar effects of sedentary work on sperm concentration
Exercise had an opposite effect: men who exercised 15 hours a week or more had 73 percent higher sperm concentrations compared to men who exercised less than five hours a week. Meanwhile, the largest study to date – including 2,261 men – found no association between self-reported physical activity and semen quality.
The researchers tried to explain this difference by pointing out that their study included a lot of men who didn't exercise at all. 'We were able to examine a range of physical activity that is more relevant to men in the general population', said Dr Jorge Chavarro, senior author of the study and assistant professor of nutrition and epidemiology at the Harvard School of Public Health.
'The majority of the previous studies on physical activity and semen quality had focused on professional marathon runners and cyclists', said Dr Chavarro. 'These professionals reach physical activity levels that most people in the world cannot match'.
However, as the study was cross-sectional – only studying one point in time – it can't answer the question whether getting off the sofa and onto the treadmill will improve sperm counts. Moreover, sperm count and concentration are only two of the many complex aspects that influence male infertility. Although the study found that physical activity had a statistically significant association with sperm quality, it's not sure whether this translates to a clinically relevant effect.
Writing in the Guardian, Professor Lord Robert Winston said he was not convinced by the findings. 'I doubt that television is the source of the problem, otherwise my own kids, who work day and night in the media, would be sterile', he wrote.
'Nor is it likely to be due to sitting long hours through the evenings on leather couches, otherwise our 92 hereditary peers would surely have died out', he added.