The research, led by David Greening of the fertility clinic, Sydney IVF, followed 118 men who had high sperm quality at the outset of the study. The team asked the men to ejaculate for seven days prior to follow−up testing, at which point they reanalyzed the quality of the men's sperm in a measure called a DNA fragmentation index. The men began the study, on average, with a fragmentation index of 34%, but at the end of the study it had fallen to 26%.
Men may actually do better to have plenty of sex in order to improve the genetic quality of their sperm.
Greening says that from the results of the study it "seems safe to conclude that couples with relatively normal semen parameters should have sex daily for up to a week before the ovulation date." While doing so may decrease the volume of sperm, this generally isn't an issue for most men, since the body produces such vast numbers of sperm on a daily basis.
Why does frequent ejaculating improve sperm's DNA? Greening suggests that it's because it restricts the amount of time the sperm sit around in the testicular ducts, where they are subject to DNA damage from reactive oxygen species like free radicals. Though these particles are a normal presence in the body, they can bring about significant damage to DNA over time.
Greening adds that "[i]n the context of assisted reproduction, this simple treatment may assist in improving sperm quality and ultimately achieving a pregnancy." Whether or not the results will hold for men who start out with below−average sperm quality will remain to be seen.