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Sperm count link to exercise still uncertain

Lazy men who spend hours watching TV could be halving their sperm count, according to a number of newspapers.

While the reports are based on proper medical research, the link between exercise and sperm count is not definitively proven.

What’s more, a man’s ability to have children is not just based on his sperm count. Male infertility problems are often complex and in many cases may not be solved by simply changing lifestyle.

The story comes from a study which found that more physical activity and less TV viewing were associated with significantly higher sperm counts.

While the results sound like yet another good reason for male couch potatoes to get more active, it is possible, for example, that an underlying factor affects how much exercise men do and their sperm counts.

Where did the story come from?

The study was carried out by researchers from several US medical schools, the University of Murcia, Spain and the University of Copenhagen, Denmark. It was funded by the National Institutes for Health in the US and the European Union.

The study was published in the peer-reviewed British Journal of Sports Medicine.

The study was reported uncritically in the Metro. The BBC and the Guardian both gave fuller accounts, including comments from independent experts.

What kind of research was this?

This was a cross-sectional study that looked at the relationship between semen quality and men’s levels of physical activity and TV watching. Semen quality is assessed by looking at sperm concentration (this is the concentration of sperm in the ejaculate, also known as sperm count), shape, movement and total sperm count (the total numbers of sperm in an ejaculate).

However, the cross-sectional design of this study means it cannot prove that physical activity and TV viewing levels directly influence sperm quality. This type of study looks at all data at the same moment in time, so it cannot be used to conclude that one thing follows another.

The authors say that semen quality seems to have declined in the past decades, but the reasons for this are uncertain. One possible reason could be the decrease in physical activity and increase in sedentary behaviour that has occurred over the same period. They also point out that strenuous, high-intensity exercise has been linked to male infertility, but the association between moderate exercise and semen quality has yet to be evaluated. The researchers add there is little research into the effects of TV watching on semen quality.

What did the research involve?

Researchers recruited 222 men, aged 18 to 22 years, from a larger study that took place between 2009 and 2010. The men were asked in a questionnaire about both their physical activity and TV watching in the previous three months. Their semen quality was assessed by sperm concentration, movement, shape and total sperm count.

The men were asked to report the number of hours spent in a normal week doing vigorous, moderate or mild exercise. Researchers wanted to know in particular about the number of hours per week of moderate-to-vigorous physical activity, defined as any exercise which “made you somewhat to very winded or sweaty”.

TV viewing was assessed in the same questionnaire by asking men to select the category of TV watching time per workday or weekend day that corresponded to their average habits over the past three months. TV watching time was categorised as:

  • none/almost none
  • 1-3 hours daily
  • 4-6 hours daily
  • 7-9 hours daily
  • over 10 hours daily

From this, the researchers analysed the average amount of time spent watching TV each week.

Semen samples were collected by masturbation at a clinic, the men were asked to abstain from ejaculation for at least 48 hours beforehand. The samples were duplicated and analysed in the laboratory within 30 minutes of collection, using accepted criteria for sperm concentration, movement, shape, and total sperm count.

Each participant was also physically examined, including assessment of weight, height, size of testicles and whether they had any genital abnormalities. The men also completed questionnaires on their backgrounds, income, medical and reproductive history, psychological stress, use of medication, smoking habits, and calorie intake.

Researchers classified the men into four groups (quartiles) according to their average moderate-to-vigorous physical activity and their TV watching per week. The association between these two factors and semen quality was evaluated using standard statistical methods. The researchers adjusted their results to take account of potential confounders such as race, smoking habits, body mass index, and calorie intake.

What were the basic results?

Of the 222 men recruited, 189 completed the study. Researchers found that:

  • sperm concentration and total sperm count were directly related to physical activity (p-trend=0.01 and 0.04)
  • men in the highest quartile of moderate-to-vigorous activity (15 hours a week or more) had a 73% (95% confidence interval 15% to 160%) higher sperm concentration than men in the lowest quartile (less than five hours a week)
  • TV watching was associated with sperm concentration and total sperm count (p-trend=0.05 and 0.06)
  • men in the highest quartile of TV watching (more than 20 hours a week) had 44% (95% confidence interval 15 to 63%) lower sperm concentration than men in the lowest quartile (0 hours per week)
  • neither physical activity nor TV watching were associated with sperm movement or shape

How did the researchers interpret the results?

The researchers say their findings suggest a more physically active lifestyle may improve semen quality. They also say that, unlike the results of previous studies, they found no detrimental effects on semen of very high levels of physical activity such as cycling and long-distance running. However, these effects may be specific to certain exercises such as cycling and long-distance running, with most of the highly active men in this study more likely play football and other sports.

The researchers say the association between TV watching and sperm count needs further research. Previous studies have suggested an association between sperm quality, sedentary activity and temperature of the testicles. However, in this study it was difficult to disentangle the effects of obesity from that of inactivity.

Conclusion

As the authors point out, this small, cross-sectional study cannot prove that more exercise and less TV will improve sperm counts in men. All it provides is a snapshot of the semen quality and the levels of physical activity and TV watching in a small group of young men, at one point in time.

It’s possible that other risk factors (called confounders) may have affected the results, although researchers tried to adjust their results for several of these. Many other factors may be involved in semen quality, including weight, smoking habits, diet, and genetics.

Also, as the researchers point out, it is unclear if the differences in sperm counts translate into clinically relevant differences in fertility. Sperm count is only one analysis performed to measure male fertility.

This type of study relied on men self-reporting both exercise levels and TV watching, which could have affected the reliability of its results.

The authors also say that the small sample size means that the results could have been due to chance. It’s worth noting that the confidence levels given in the results are very wide, which indicates the results may not be reliable. For example, men in the highest quartile of moderate-to-vigorous activity had from 15% to 160% higher sperm concentration.

It would be nice to know if a more active lifestyle had the bonus effect of increasing sperm counts as well as being good for health overall, but this research alone does not provide a definitive answer and should be seen in the context of other studies.

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