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%.
The researchers at Massachusetts General Hospital, Boston, told a conference in Hawaii 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 of beer a night could improve their fertility.
Current NHS advice 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 reduce stress levels and help conception.
‘Anything that is good for your heart health is also good for your fertility’
The study looked at 105 men of an average age of 37 whose wives or girlfriends were undergoing IVF at the Massachusetts 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 chances,” said lead author Dr. Anatte Karmon, an obstetrician who works at 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 Karmon. “So do physical exercise and eat a well-balanced diet.”
The study found that neither caffeine nor alcohol affected the number of sperm, their shape or how well they swum. But there was an effect when caffeine and alcohol levels were compared with the odds of having a baby.
Dr. Allan Pacey, a senior lecturer in andrology at the University of Sheffield, said: “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.