Scientists discover that between June and August men have double the risk of misshapen or slow sperm, making it harder for couples to conceive.

The balmy nights of summer might seem like the perfect setting for romance but if you're trying for a baby, it may not be the best time to begin.

Scientists at the Universities of Sheffield and Manchester have discovered that between June and August, men have double the risk of misshapen or slow sperm, making it harder for couples to conceive.

Although they did not look into what might cause the effect, they speculate that a lack of daylight and vitamin D may be responsible, as sperm that is present in summer has actually formed in the spring.

But while the research identified seasonal differences in the quality of men's sperm, experts found that drinking and smoking do not have any impact, meaning potential fathers may not have to abandon their vices while trying to start a family.

Poor sperm quality

The discovery of poorer quality summer sperm is roughly reflected in birth rates in the UK, where the majority of babies are born around April and May, suggesting they have been conceived after August.

Lead author Allan Pacey, senior lecturer in Andrology at the University of Sheffield, said: "The most obvious explanation is that it is to do with higher temperatures but they we looked at the impact of tight underwear, which also causes a rise in temperature, and that had no impact on sperm shape.

"If a man ejaculates in August his sperm is made three months before.

"We could speculate that it may be things like daylight or a lack of vitamin D but we don't know.

"But people shouldn't stop trying during the summer months because the most important thing for people trying to conceive is having a lot of sex." The shape of the sperm is important for conception, because sperm with misshapen heads struggle to get through the cervix.

Laboratory studies also suggest that poorly shaped sperm also swim less well because their abnormal shape makes them less efficient.

However, the study also found that unhealthy lifestyles such as smoking and drinking were unlikely to have any impact on sperm health.

But the academics found that smoking cannabis doubled the chance of sperm being misshapen and swimming more slowly.

"Our knowledge of factors that influence sperm size and shape is very limited, yet faced with a diagnosis of poor sperm morphology, many men are concerned to try and identify any factors in their lifestyle that could be causing this," Pacey added.

"It is therefore reassuring to find that there are very few identifiable risks, although our data suggests that cannabis users might be advised to stop using the drug if they are planning to try and start a family."

Lifestyles

The study, published in the medical journal Human Reproduction, recruited 2,249 men from 14 fertility clinics around the UK and asked them to fill out detailed questionnaires about their medical history and lifestyles.

They found that men who had fewer than 4 percent normal sperm were twice as likely to have produced a sample in the summer.

Andrew Povey, from the University of Manchester's Institute of Population Health, said: "This research builds on our study of two years ago which looked at the risk factors associated with the number of swimming sperm in men's ejaculates.

"This previous study also found that there were relatively few risk factors that men could change in order to improve their fertility.

"We therefore have to conclude again that there is little evidence that delaying fertility treatment to make adjustments to a man's lifestyle will improve their chances of a conception."

A previous study by the same teams found tight underwear lowered the number of sperm produced, but the new research found it did not impact on the shape of the head movement.

(China Daily 08/02/2014 page23)