Drinking too much coffee can radically reduce a man’s ability to father children, a study has found.
Men who drank two or more cups of strong coffee a day had just a one in five chance of becoming fathers through IVF.
However, for those who drank less than a cup, the chance of having a child rose to nearly 52 per cent.
The researchers at Massachusetts General Hospital, Boston, believe that caffeine may harm sperm at a molecular level.
A shot of espresso contains around 100mg of caffeine. Those men who drank 265mg or more had the least chance of becoming fathers.
The study also showed that men who drink around a pint and a half a night could improve their fertility.
Current NHS advices suggests that men should not drink more than four units a day, the equivalent of around two pints of beer.
The research found that men who drank at least 22g of alcohol per day, or three units, were more than twice as likely to have children through IVF than those who abstained.
Health experts say that moderate amounts of alcohol may reduced stress levels and help conception.
The study looked at 105 men of an average age of 37 whose wives or girlfriends were undergoing IVF at Massachusetts General Hospital between 2007 and 2013.
“High male caffeine consumption appears to reduce couples’ chance of achieving a clinical pregnancy, while male alcohol consumption appears to enhance their changes, said lead author Dr Anatte Karmon, an obstetrician, Massachusetts General Hospital.
But she advised that men should keep their lifestyle as healthy as possible if they were hoping to become fathers.
”Anything that is good for your heart health is also good for your fertility,” said Dr Karmon.
“So do physical exercise and eat a well-balanced diet.”
The study found that neither caffeine nor alcohol affected the number of sperm, shape or how well they swum.
But she did find an effect when she compared caffeine and alcohol levels with the odds of having a baby.
Dr Allan Pacey, Senior Lecturer in Andrology at the University of Sheffield, said that alcohol may help because it reduces stress.
“There has been conflicting data about the benefit or harm or drinking alcohol when trying to conceive with the potential for different effects on men and women,” said Dr Pacey.
“However, I firmly believe that moderate social drinking within guidelines (3 to 4 units per day) can be of benefit for couples trying to conceive, either naturally or during assisted conception because it helps to reduce stress.
“I see no reason to advise couples attempting IVF to become teetotal, but they clearly need to drink alcohol sensibly and be advised that if the female partner falls pregnant she needs to stop at that point to ensure the development of the baby is not harmed.
“The fact that caffeine consumption in the male partner may reduce IVF outcome is intriguing and needs further exploration.”
The study was presented at the American Society for Reproductive Medicine annual conference in Hawaii.
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