Over the past couple of weeks we've been hit with news reports about cannabis being bad for sperm (but tobacco and alcohol not having much effect - see BioNews 757) and mobile phones also being potentially damaging (see BioNews 758).
Here, I want to look at the strengths, weaknesses and implications of the papers behind the headlines.
Summary and strengths
The paper that produced the headlines about cannabis (1) is another interesting, if rather belated, set of results from the CHAPS-UK study that was performed in 1999-2002. CHAPS-UK was a multi-centre, case-control study designed to provide adequate power to identify the impact of a range of lifestyle and occupational risk factors on semen quality.
The final data was from 318 cases and 1,652 controls, from 11 fertility clinics around the UK, making it one of the largest studies on the subject. In a small subset of 162 men, the use of cannabis in the three months prior to the study was associated with a greater likelihood of having less than ten percent of sperm being of normal appearance (morphology).
The overall summary was that common lifestyle choices make little contribution to the risk of poor sperm morphology. The authors also concluded that 'delaying assisted conception to make changes to lifestyle was unlikely to enhance conception'.
In the study, less than half of the men met the eligibility criteria and of those who did, two-fifths declined to participate, reducing the numbers significantly. This meant that the study had less cases that in the original design and probably not enough cases to draw definite conclusions.
Furthermore, no tests were performed to detect actual levels of drugs, tobacco or alcohol in the bloodstream. All the data was self-reported. Lifestyle studies require honesty and it is always hard to gauge how accurate such data is. For example, our centre in Belfast was heavily involved in the study and our experience was that men needed to be interviewed alone, since answers given with partners present were rather more conservative. Even in a major study like this, if risk factors are under-reported, then to conclude that few of these factors matter is an unsafe message to give the public.
I agree that, in this study, lifestyle had little impact on sperm morphology. However, I do not accept the quantum leap to the statement that 'delaying assisted conception to make changes to one's lifestyle is unlikely to enhance conception'.
There is an underlying assumption that sperm morphology has a major impact on conception. This is based on a paucity of supporting studies as the authors themselves admit. In the latest British Fertility Society guidelines for andrology (2), morphology is seen as the least valuable parameter in a semen analysis.
In an attempt to strengthen the importance of sperm morphology, the authors state in their introduction that poor morphology is thought to be associated with increased DNA fragmentation citing data from the World Health Organisation (WHO). This association is not well supported in current literature. If it were, there would be no need for the burgeoning interest in sperm DNA damage testing.
The other issue I have with this study is much broader. In my opinion, when scientists speak to the public we need to base our results in context of what we know from other relevant studies which the public will not be familiar with. In the case of the cannabis data, comments from authors to the press that men would be 'back to normal' fertility-wise after three months post-use seem unwarranted.
Our group published a study in 2012 (3) based on giving given rats a drug which acts on the same receptors as cannabis. The study was designed to imitate daily moderate use of cannabis over a couple of years. We found that sperm counts were markedly depleted.
Of even more concern, the Sertoli cells were also reduced. These cells each nurture a finite number of sperm and are irreplaceable post-puberty. With this data in mind, a 'return to normal', is unlikely to occur. Also, to propagate the notion that cannabis is a harmless pleasure seems unwise, given what we know about the health consequences of cannabis. This month a review in the New England Journal of Medicine (4) outlines the adverse effects of cannabis on brain development, academic achievement and even mentions the increased risk of traffic accidents.
Summary and strengths
The 'mobile phone study' was in fact a systematic review and meta-analysis (5) of ten studies that had measured exposure to electromagnetic radiation from mobile phones and had tested nearly 1,500 semen samples obtained from men attending fertility clinics and research centres.
This is a very important area of research, given the ubiquitous use of mobile phones. Effects on sperm count were inconsistent. Overall viability and motility were reduced by around eight percent. Is this clinically relevant? Given that the WHO defines clinical motility and viability problems as starting at 40 percent and 58 percent reductions from normal, respectively, there's clearly some room for manoeuvre with these measurements.
Systematic reviews often have problems because the individual studies they draw on can vary in their design. So, here, there's variation in the level of irradiation, the exposure duration and the way in which it was administered. On some occasions the semen had been exposed to irradiation in a petri dish in the lab rather than via a mobile phone to the ear! Data were, again, self-reported leading to possible inaccuracy. Men had been recruited from fertility clinics so already had fertility issues. No consideration was taken of their other lifestyle habits.
The headlines seemed to become gradually more hysterical throughout the day. From 'Can cell phones make you sterile?' to 'Your cellphone is killing your sperm' and, finally, 'Mobile phones damage chance of fatherhood'.
The 24-hour news cycle, which flashes complex scientific studies in front of our eyes before whisking them away again, can bewilder its public. As one of the Science Media Centre's pool of experts, I am often asked to comment on the validity of andrology studies. I believe, as scientists, our response should usually be one of caution and that we should steer clear of absolutes; if we can we should try and stop Chinese whispers before they gain serious traction.