Scrotal heat stress causes sperm chromatin damage and cysteinyl aspartate-spicific proteinases 3 changes in fertile men.
Plain-language summary
This study set out to see what sustained scrotal heating does to semen and to the sperm's genetic material in fertile men. Nineteen healthy volunteers wore a warming belt at 40 to 43 degrees Celsius (104 to 109 degrees Fahrenheit) for 40 minutes a day, two days a week, for three months. Semen was analyzed before, during and after, along with the activity of Caspase-3, an enzyme the body switches on when a cell is being dismantled, so a rise in it means more sperm are being taken apart and lower is the healthier direction. Sperm concentration, movement and normal shape all fell during the heating, sperm DNA fragmentation (breaks in the genetic material inside sperm, where more breaks mean a lower chance of conception) rose, the packing of the sperm's genetic material was disturbed and Caspase-3 activity rose. Three months after the heating stopped, the measures had returned to their starting levels. This comes from the same laboratory and the same warming protocol as another study in this library, on nitric oxide and MIF, so the two are one line of evidence rather than two.
Key findings
- Sperm concentration, movement and normal shape all fell during the three months of heating at 40 to 43 degrees Celsius (104 to 109 degrees Fahrenheit).
- Sperm DNA fragmentation (breaks in the genetic material inside sperm, where more breaks mean a lower chance of conception) rose during heating, and the sperm's chromatin packing was disturbed.
- Caspase-3 activity, a marker of cells being dismantled, rose during heating.
- Three months after the heating stopped, the measures had recovered to their pre-heating levels.
- White blood cell counts in semen rose and fell together with Caspase-3 activity.
How to analyze the study yourself
- Study type
- This design tracks changes in the same group over time, showing how heat exposure affects sperm, but it cannot prove heat alone caused the changes without a control group.
- Population
- Healthy, fertile male volunteers.
- Funding
- Not reported
- Takeaway
- This study found that heating the scrotum to 40 to 43 degrees Celsius (104 to 109 degrees Fahrenheit) for 40 minutes twice a week lowered sperm count, movement and normal shape and damaged the sperm's DNA, in men who were fertile to begin with, and that the measures had recovered three months after the heating stopped. If you are trying to conceive, it is worth getting regular heat sources off your testicles about three months ahead, which is what this study measured rather than a rule of thumb.