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.
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
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
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
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.
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
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.