Frequent sexual activity improves the genetic quality of sperm and may help some couples conceive, fertility specialists have found.

A study of men attending a fertility clinic revealed that genetic defects in their sperm fell substantially after going on a programme that required them to engage in sexual activity daily for a week. Fertility doctors commonly advise men trying for a baby to abstain from sexual activity for two to three days, because it boosts the number of sperm they produce. The latest finding suggests that men who have healthy sperm counts but poor quality sperm can improve the genetic material in the cells by engaging in sex more often.

Genetic damage can reduce the chances of a sperm fertilising an egg, or can lead to the formation of an embryo that fails to implant properly or is miscarried.

David Greening, a fertility doctor at Sydney IVF, studied 42 men whose sperm had high levels of genetic damage. All of the men were from couples who had a history of recurrent miscarriage or failed IVF treatment. After three days of sexual abstinence tests revealed 30.8% genetic damage in the men's sperm. The men were tested again after being told to engage in sexual activity daily for a week. Tests showed that while their sperm counts fell by nearly one third, genetic damage also fell, on average by 12.8%, in 37 of the men. Tests on the remaining five men showed their sperm had slightly increased genetic damage. Around a fifth of men have sperm with significant DNA damage.

Dr Greening, who spoke at the American Society for Reproductive Medicine meeting in Washington yesterday, said: "I'm convinced that ejaculating more frequently, ie daily, improves sperm DNA damage in most men by a decent amount." He believes that the longer sperm are held in the tube that leads from the testicles the more genetic damage they accumulate from free radicals circulating in the body.

Allan Pacey, senior andrologist at Sheffield University and secretary of the British Fertility Society, said: "If you ejaculate every day then you're preventing the sperm being in the reproductive tract for too long, so it makes sense that they're less exposed to damage and it's fresher."

In 2003 another team of Australian fertility researchers reported that men could reduce their risk of developing prostate cancer by masturbating frequently. The team, at the Cancer Council Victoria in Melbourne, believed that ejaculating prevented the buildup of cancer-causing chemicals in the prostate.