Changes in Levels of Seminal Nitric Oxide Synthase, Macrophage Migration Inhibitory Factor, Sperm DNA Integrity and Caspase-3 in Fertile Men after Scrotal Heat Stress.
Plain-language summary
This study looked at what sustained scrotal heating does to semen and to the sperm's genetic material in already fertile men. Twenty-five 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, alongside three markers, on all three of which a rise here is the unwanted direction: nitric oxide (a gas cells release as a signal, which damages sperm membranes and DNA when it runs high in semen), MIF (macrophage migration inhibitory factor, an immune signal that holds inflammatory cells in place, so a rise means inflammation) and Caspase-3 (an enzyme a cell switches on to dismantle itself, so a rise means more sperm being taken apart). Sperm concentration, movement and normal shape all fell, the sperm's DNA and packaging were damaged, and all three markers rose. Three months after the heating stopped, everything had returned to starting levels. This comes from the same laboratory and the same warming protocol as another study in this library, on sperm chromatin damage and Caspase-3, 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.
- Sperm DNA fragmentation (breaks in the genetic material inside sperm, where more breaks mean a lower chance of conception) rose during heating.
- Nitric oxide and the enzyme that makes it, nitric oxide synthase, rose in the seminal fluid, as did MIF, and Caspase-3 activity rose inside the sperm themselves. All three rising is the unwanted direction on all three.
- 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 the inflammation and cell-death markers.
How to analyze the study yourself
- Study type
- This study used a controlled exposure design to track changes in sperm health over time, which helps show how heat affects sperm, but it cannot prove long-term effects beyond the study period.
- Population
- The study included 25 healthy adult men.
- 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, damaged the sperm's DNA and raised markers of inflammation, in men who were fertile to begin with. The measures had recovered three months after the heating stopped, which is the useful number here: the damage is not permanent, and it is also not gone the week you stop. If you are trying to conceive, it is worth getting regular heat off your testicles well ahead of time.