Coffee may not simply wake up the brain cells - it could also boost male fertility, new research suggests.

Scientists have found that men who drink coffee have sperm that moves better than the sperm of those who lay off the caffeine. The study suggests that new coffee-based treatments should be developed for men with poor sperm movement - a defect that can cause fertility problems.

The findings will be presented later this week at the annual American Society for Reproductive Medicine conference in Texas.

Brazilian researchers tested the sperm motility - the strength and endurance of sperm as they swim towards the egg during fertilisation - of 750 men awaiting vasectomy operations. Doctor Fabio Pasqualotto, the lead researcher, said: 'Sperm motility was higher in patients who drink coffee compared to patients who do not drink coffee.'

The researchers also found that smoking had neither a beneficial nor an adverse effect on sperm motility compared with the caffeine effect.

Doctor Euan Paul, spokesman for the Coffee Science Information Centre, said: 'These findings are very exciting. There has been growing concern about sperm problems and about lack of fertility in particular.' Doctor Paul said that since caffeine acted as a stimulant on dopamine cells in the brain, helping people to concentrate, there was a possibility that sperm also experienced a boost when a man drank caffeine.

? New evidence that smoking cannabis can affect fertility, particularly in women, was also presented at the conference in San Antonio.

Scientists from New York University examined the sperm of 22 men who admitted smoking cannabis at least four times a week for the past five years. They found that the sperm may not be capable of the hyperactivity needed to fertilise the egg and also reduced the number and volume of sperm in men.

But women were found to be more seriously affected with toxins from the drug left in their reproductive tracts.

Doctor Simon Fischel, who heads the CARE fertility unit at Park Hospital in Notting-ham, said: '[Women] have a fixed egg production, which means any damage may be difficult to overcome.'

He added: 'With men, providing there isn't any damage to the stem cells responsible for sperm production, there may not be any lasting harm if they stop using the drug, because sperm is continually being made.'