Fertility: underpants news is overblown

Men trying to improve their sperm count “can ditch the healthy living advice but should think carefully about their underwear”, said The Independent. Apparently the type of undies you wear has more influence over your sperm quality than smoking, drinking or an unhealthy diet.

Before dads-to-be ponder the boxers-vs-briefs debate over a beer, a cigarette and a burger, it should be noted that the research behind today’s attention-grabbing headlines does not suggest that unhealthy living is not detrimental to sperm quality. The news is based on research looking at the lifestyles and medical histories of only men with fertility problems, who had sperm with either normal or reduced motility (movement). As such, it was only in a specific group with fertility problems and tells us very little about the general population or the effects of these vices. Also, the study has not explored the reasons the men were experiencing fertility problems.

Researchers found no association between sperm motility and smoking, alcohol, recreational drug use or being overweight, although wearing tight underwear was associated with reduced motility. However, given the limited nature of the research and the mystery over the specific causes of participants’ fertility problems, little can be concretely concluded from this study.

The National Institute for Health and Clinical Excellence (NICE) is currently updating its guidelines on fertility. NICE’s current guideline advises doctors treating male fertility problems to consider several lifestyle factors, including alcohol intake, smoking, wearing tight underwear, having a BMI of over 29 and the use of recreational drugs.

Where did the story come from?

The study was carried out by researchers from the University of Manchester, the University of Sheffield and the University of Alberta in Canada. It was funded by the UK Health and Safety Executive, the UK Department of Environment, Transport and the Regions, the UK Department of Health and the European Chemical Industry Council. The study was published in the peer-reviewed journal, Human Reproduction.

The study was covered fairly in the press, although both The Independent and the Daily Mail said that lifestyle factors had not been found to harm “male fertility”. This is misleading as all men in this study – both the “cases” with low sperm motility (movement) and the “controls” without – were having fertility problems.

As the study has not explored the reasons the men were experiencing fertility problems we don’t know whether having sperm with low motility provided the whole answer to the problem in the cases, and we don’t know the reasons behind the fertility problems in the control group. Therefore we can make no assumptions from this study over whether any of the medical or lifestyle factors examined are related to fertility or indeed how they might be.

What kind of research was this?

The researchers pointed out that although men who wish to father a child are often advised to live a healthy lifestyle, they felt the research on this issue is contradictory and the strength of the evidence weak.

Their case-control study included men who were all attending a fertility clinic. The researchers looked at whether a number of lifestyle, health, social and other factors were more or less common in men who had low sperm motility (the “cases”) compared with those who did not have low sperm motility (the “controls”). This type of study can only tell us which factors are more or less common in men with low sperm motility who are experiencing fertility problems, compared with men who are experiencing fertility problems but have normal sperm motility. It can tell us little more than this and cannot establish any cause and effect relationships between these factors.

What did the research involve?

Cases and controls were recruited from 14 fertility clinics across the UK during a 37-month period starting in January 1999. They were identified at their first visit to a fertility clinic or to a laboratory for semen analysis. The men, aged 18 or over, were eligible to take part in the study if they had been attempting conception without success following at least 12 months of unprotected intercourse.

They also had to have no knowledge of the result of any semen analysis – knowing so could have potentially introduced bias when participants reported details such as lifestyle factors. Men with known medical problems which can cause fertility problems, or who had had treatment which can cause fertility problems, were excluded.

Recruits were asked to complete a brief questionnaire on job history, lifestyle and health factors. They were also asked to abstain from ejaculation for a period of three-to-five days before a clinic visit. At the clinic visit they were asked further questions about their lifestyle, fertility history and the type of clothing and underwear they wore. Recruits joining the study after December 1999 were also asked about their ethnic group, height and weight.

The researchers used semen samples which had been provided by the men as part of infertility investigations with their partner. The semen was analysed for its motility in quality-assessed UK laboratories according to accepted protocols. They based their definition of low motile sperm concentration on the World Health Organization’s recommendations on what constitutes “normal” sperm count and motility. However, they also found that motile sperm count (MSC) was strongly related to the period of abstinence from ejaculation, so took this into account in their analysis.

The men were then divided into the following two groups:

those who were found to have low sperm motility (780 cases)
those whose sperm motility was “normal” (1,469 controls)

The researchers analysed any association between low MSC and the information they had on lifestyle, health and other factors. They adjusted their results for a range of factors which might have affected the results.

What were the basic results?

The researchers found that compared with controls, cases with low MSC were more likely to:

have a history of testicular surgery (odds ratio [OR] 2.39, 95% confidence interval [CI] 1.75 to 3.28)
be in manual work (OR 1.28, 95% CI 1.07 to 1.53) or be out of work (OR 1.78, 95% CI 1.22 to 2.59)
be of black ethnicity (OR 1.99, 95% CI 1.10 to 3.63)

The researchers found that compared with controls, cases with low MSC were less likely to:

wear boxer shorts (OR 0.76, 95% CI 0.64 to 0.92)
have had a previous conception (OR 0.71, 95% CI 0.60 to 0.85)

No significant association was found with smoking and alcohol consumption, the use of recreational drugs, a high BMI or having a history of mumps or fever.

How did the researchers interpret the results?

Other than wearing loose underwear (avoiding tight ones) and avoiding exposure to certain chemicals in certain manual jobs, the researchers say their study identified “few modifiable risk factors” for low motility in sperm. They said their results suggested that “delaying assisted conception to make poorly evidenced changes to lifestyle is unlikely to enhance the chance of conception and may indeed be prejudicial in couples with little time to lose”.

Conclusion

The results of this study should be interpreted with caution and there are important limitations to bear in mind. All the men in this study – both those with low sperm motility and the comparison group without – were seeking fertility treatment. The study has not explored the reasons these men were experiencing fertility problems, and therefore we don’t know whether low sperm motility was the sole cause of the case participants’ infertility, and we don’t know the reasons behind the fertility problems in the control group. This means we can make no assumptions from this study on how, if at all, any of the medical or lifestyle factors examined are related to fertility.

We cannot even conclude that these factors are related to “sperm quality” as a complete measure: a range of different properties are used to assess the overall quality of a semen sample, but in this study researchers only looked at the concentration of sperm that were actively moving. For instance, they did not look at measures such as the size and shape of sperm, which are other important indicators of quality, nor the integrity of DNA in the sperm.

It is also worth noting that the researchers have examined a wide range of potential medical and lifestyle factors, which increases the possibility that associations will be found by chance. Also, this type of study is more likely to pick up something by chance given that it was not testing something specific – such as whether smoking is associated with low sperm count – which would have made the results more reliable. The study also relied on men self-reporting their lifestyle habits, which means the results may be less reliable.

Furthermore, as the researchers pointed out, of those men who met the criteria for the study, two-in-five weren’t recruited. It is possible that many men refused to take part because they had a lifestyle they did not want investigated.

Overall, this study tells us that among men attending a fertility clinic, certain medical and lifestyle factors were found to be more common in those who had fewer motile sperm, but little more can be concluded from this. For example, it can’t be concluded that these factors are a cause of male fertility problems.