The last week has seen a handful of discoveries about sperm. Coffee speeds up sperm, cannabis makes them speed up and burn out quickly, and overweight men suffer from sperm DNA fragmentation. Researchers from Brazil found that men who drink coffee have higher sperm motility compared to non coffee drinkers, which means that in the future caffeine could be used as the basis of an infertility treatment for men. Cannabis contains an active compound called tertahydrocannabinol or THC, which can acts on receptors found in human sperm. Previous studies have shown that THC can stop sperm from binding to eggs and This new study from researchers in America, looked at sperm from 22 cannabis smoking men, revealed that they became prematurely hyperactive, which could lead to reduced fertilising capacity as the sperm can burn out too early before reaching the egg. Cannabis smoking could also reduce female fertility by raising levels of THC in their reproductive tract, which could then impact sperm. A third study showed that overweight men have reduced fertility due to DNA fragmentation in their sperm. A team from Atlanta Georgia, were the first to compare men's body mass index or BMI (which is weight in kgs, divided by the height in metres, then divided by the height again) with the integrity of a protein called chromatin, which is crucial for the structure of DNA. And they found that as BMI goes up so does the rate of DNA fragmentation. Other factors that are thought to increase sperm DNA fragmentation are being over 50 years old, smoking and being exposed to air pollution.