TOO much alcohol can affect a man's performance in the bedroom - but the occasional pint of beer or glass of wine could actually improve male fertility and sexual function, according to a new study.
By contrast, drinking coffee and other caffeinated beverages makes men less likely to conceive with their partner, researchers found.
And another study showed that eating meat increases sperm density, compared to consuming a vegetarian or vegan diet.
Researchers presenting at the 70th Annual Meeting of the American Society for Reproductive Medicine in Honolulu, Hawaii, revealed the impact of various lifestyle factors on men's ability to conceive.
A group from the University of Rochester Medical Center in Rochester, New York, studied 753 men undergoing fertility treatment between 2003 and 2011, asking them about their drinking and smoking habits, as well as their sexual health and satisfaction. The average age of the men was 35.
Almost three-quarters (73 per cent) of those surveyed drank alcohol, while only 16 per cent used tobacco. The results showed that drinkers reported better sexual function than teetotallers, while those who didn't drink alcohol were more likely to report deficiencies in their erections and ability to complete intercourse.
By comparison, 8.4 per cent of the smokers had moderate to severe erectile dysfunction and were more likely to be unsatisfied with sex than non-smokers.
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However, not all beverages have a positive impact. Between 2007 and 2013 men who underwent IVF at Massachusetts General Hospital were asked about their pre-treatment diet, including their consumption of alcohol and caffeine.
Analysis of the data showed that couples where the male partner's caffeine consumption fell in the highest range - more than 265 milligrammes or about three eight ounce cups a day - were only half as likely to have a clinical pregnancy as couples where the man consumed less than 88 milligrammes of caffeine a day.
Meanwhile, researchers from Loma Linda University School of Medicine, in California, found that vegetarian men have significantly poorer sperm concentration and mobility than those who eat meat.
The study compared results from sperm analyses conducted between 2009 and 2013 on 26 vegetarians, 5 vegans, and 443 non-vegetarians. The vegetarians had an average sperm concentration of 51 million/millilitre compared to 70 million/millilitre for meat eaters, as well as lower average sperm mobility: 33 per cent compared to 58 per cent. Vegans' results were similar to vegetarians'.
However, the lower results were not classified in the infertile range, meaning that all the numbers fell in the normal range.
ASRM President Rebecca Z Sokol: "The human organism is complex and substances we inhale and imbibe have systemic effects beyond the stimulation the user is seeking.
"These studies provide new information that can help men make healthy choices for themselves, their partners, and their future children."