The researchers suggest that ejaculating may prevent carcinogens accumulating in the prostate gland.

The prostate provides a fluid into semen during ejaculation that activates sperm and prevents them sticking together.

The fluid has high concentrations of substances including potassium, zinc, fructose and citric acid, which are drawn from the bloodstream.

But animal studies have shown carcinogens such as 3-methylchloranthrene, found in cigarette smoke, are also concentrated in the prostate.

"It's a prostatic stagnation hypothesis. The more you flush the ducts out, the less there is to hang around and damage the cells that line them."

Dr Giles said fewer ejaculations may mean the carcinogens build up.