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Scientists publishing in Occupational & Environmental Medicine report that exposure to air pollution – in Taiwan – is associated with a lower level of normal shaped sperm and a higher level of sperm concentration.
Prof. Allan Pacey, Professor of Andrology, University of Sheffield, said:
“Overall this appears to be a well conducted study, which examines the relationship between fine particulate matter in the air and measurements of semen quality in men from Taiwan. The authors appear to have used robust methodology throughout their study and furthermore an advantage of their design is that they seem to have used data on air quality collected from satellites rather than conventional air monitoring stations at ground level. This makes their exposure data more precise and more specific to the men who provided semen samples.
“The main result of the paper appears to be that as the concentration of fine particulates increases, then so does the proportion of sperm which are abnormally shaped. At first glance, this may seem quite an interesting result. However, we know that the assessment of sperm size and shape (sperm morphology) is one of the most difficult tests to carry out on sperm (and therefore can be less accurate). Moreover, many doctors and scientists now believe that on its own poor sperm morphology is probably not as clinically relevant as we once thought it was. So, whilst the authors have found a potentially interesting biological result, I am not sure it is that clinically meaningful.
“Of further interest is their observation that as the concentration of fine particulates increases then so does the sperm concentration. This makes no sense to me and does not fit with any biological mechanism that I am aware of.
“However, from this and other studies, I remain of the opinion that air pollution probably does have the potential to negatively influence male reproductive health. But the jury is still out about quite how and to what extent this impacts on male fertility, rather than measurable and small interesting changes in semen quality.”
Prof. Kevin McConway, Emeritus Professor of Applied Statistics, The Open University, said:
“This is an interesting study, but it’s important to be aware of its limitations. If I were young enough to worry about my fertility, I wouldn’t put moving to an area with cleaner air at the top of my list of actions – though there are certainly many other health-related reasons to live in cleaner air.
“It’s good that the researchers used a measure of pollution by fine particulate matter on a fairly high-resolution scale (1 square kilometre), but it’s also important to think about what this means. The men involved were under 50 years old, and presumably most were in work. Many probably worked more than 1 kilometre from their home, and so spent a good proportion of their time in a place where the air pollution level might have been quite a lot different from where they lived. The researchers did not take into account other air pollutants, and many such pollutants tend to go together, so that if fine particulates are high, some other pollutants are likely to be high as well. So if there really is an effect on sperm characteristics, maybe it could be caused by different pollutants.
“This is an observational study, so in any case it can’t be clear on what might cause what. The media release rightly makes this explicit. The problem is that there might be factors that happen to be associated both with particulate pollution and with sperm abnormalities, and it may be these factors that are the cause of the sperm problems and not the particulate pollution at all. I’ve already mentioned that other pollutants may act in this way, but there are other possibilities. People who live in areas of high air pollution tend to be different from those in areas of low pollution in several ways. For instance, they may tend to work in different jobs, and there are several occupational factors that have been linked to fertility problems in previous studies. The researchers did take account, statistically, of several such factors, such as the men’s age, education, body mass index (which measures overweight) and whether they smoked or drank alcohol, but, for example, they had no information on where the men worked and only limited information on their exposure to possible harmful effects at work, so couldn’t take everything into account. So there has to remain doubt as to whether particulate pollution, or indeed any kind of air pollution, is a cause of semen abnormality.
“It’s also important to bear in mind that the data for this research came from men in Taiwan who volunteered for the study, and the research report makes it clear that they were not particularly representative of all Taiwanese men (for instance, they were better educated on average), let alone men on other countries. Also, the levels of fine particulate pollution in Taiwanese cities have, for several reasons, been higher than in British cities. London and other big British cities do have some air pollution ‘hotspots’, but overall the level tends to be considerably lower than in Taiwanese cities. Also, the size of the correlations between air pollution and sperm abnormality in the Taiwanese study are not enormous. The press release says the association is “strong”, but what they mean is that there is good statistical evidence that it exists, but not that it is causal, and not that the actual lowering of sperm quality when there is a given amount of extra pollution is large. The researchers are right to point out that health effects of air pollution can be important even if they are not large on an individual basis, because so many people can be affected, but they do rightly hedge their conclusions by using the words “if” and “may”.”
Prof. Sheena Lewis, Emeritus Professor of Reproductive Medicine, Queen’s University (QUB), said:
“The effects of air pollution on sperm shape are small despite the study being very large. Also, the authors’ suggestion that sperm numbers have increased to compensate for poor sperm shape has little scientific basis. Although these data may be unimportant as potential causes of male infertility they provide an important public health message on the dangers of pollution if we accept that sperm health is a strong indicator of our overall male health.”
* ‘Exposure to ambient fine particulate matter and semen quality in Taiwan’ by Lao et al. will be published in Occupational & Environmental Medicine on Tuesday 21 November.
Declared interests
Prof. Allan Pacey: “Chairman of the advisory committee of the UK National External Quality Assurance Schemes in Andrology, Editor in Chief of Human Fertility and Trustee of the Progress Educational Trust (all unpaid). Also, recent work for the World Health Organisation, British Broadcasting Corporation, Purple Orchid Pharma (paid consultancy with all monies going to University of Sheffield). Co-applicant on a research grant from the Medical Research Council (ref: MR/M010473/1).”
Prof. Kevin McConway: “Kevin McConway is the lead author of a chapter on Measurement and Communication of Health Risks from Pollution for a forthcoming Annual Report of the Chief Medical Officer. He is a member of the Science Media Centre’s Advisory Committee.”
Prof. Sheena Lewis: Sheena is CEO of SpermComet Ltd, a university spin-out company marketing a test for male infertility: www.spermcomet.com.