"Men who wear kilts are more fertile – because their sperm are cooler," is the claim on the Mail Online website.
This claim is based on an unusual study that seems to be an exploration of the joys of kilt wearing rather than a serious scientific paper.
That is not to say that the theory presented by the author of the study – who happens to be Dutch not Scottish – is implausible. There is some evidence that heat may have a negative effect on sperm quality and keeping your testicles moderately, but not uncomfortably, cool can help increase sperm production.
The problem with the study of kilt wearing is that the author has provided no scientific evidence to support his theory.
Men worried about their sperm production who are on a tight budget are advised to invest in a few pairs of loose-fitting boxer shorts rather than a kilt.
Read more on how to improve your chances of becoming a father.
The study was carried out by a researcher from Erasmus MC University in the Netherlands. No conflicts of interest were declared.
The study was published in the peer-reviewed Scottish Medical Journal.
The Mail Online’s reporting of the study was very poor. It failed to mention the fact that the author provided no scientific evidence to support his theory.
It also carried a number of quotes from the author that were not subject to any scrutiny, including “A kilt will get you noticed no matter where you are”, “Men wearing a kilt experience a strong sense of freedom and masculinity” and “Many women are attracted to men in kilts”.
This was an opinion piece offering theories relating to scrotal temperature, sperm development and male fertility. In particular, the researcher looked for evidence on the possible benefits of kilt wearing for sperm quality. He found none.
As this was an opinion piece and review, no systematic search of the scientific literature was conducted. In this type of review, studies may be identified on their availability or on author selection, so they are frequently open to bias. If no studies are identified, it is hard to say whether there was no evidence at all on the effects of kilts on male fertility, or none that suited the findings the author was looking for. This unscientific approach serves better for a magazine feature or blog post than a peer-reviewed medical journal article.
The author says that there are anecdotal reports that men who wear Scottish kilts have better sperm quality and better fertility. He also says recent studies have shown a global fall in sperm counts over the past 50 years, with a decline in fertility rates observed in the western world.
Sperm motility (how quickly a sperm can swim towards an egg) and sperm count are the best predictors of male fertility. Both of these factors seem to be affected by an increased scrotal temperature, and clothing has been implicated in increasing scrotal temperature to a level that may negatively affect sperm development.
There may be a case, the researcher argues, that men should wear skirts and avoid trousers, at least while they are trying to conceive children. As many men will have an aversion to wearing skirts, a kilt may be a more suitable alternative, the researcher suggests. He says that men “experience a strong sense of freedom and masculinity and that many women are attracted to men in kilts”.
Traditionally, Scots “go regimental” (meaning they do not wear anything underneath their kilts). This leaves the testicles uncovered, potentially lowering their temperature, and thereby, theoretically, improving sperm quality.
The author suggests that the fact that the sperm quality of Scottish men has declined in recent years could be explained by the decline in kilt wearing since the 1950s.
The author looked for and quoted some literature on scrotal temperature, sperm development and fertility. He also conducted a search of two online research libraries using the terms “kilt”, “sperm” and “fertility” to try to identify studies linking kilts with fertility or sperm quality.
The author says he found no trials of “therapeutic kilt wearing” in relation to sperm quality. He says there are some old anecdotal publications that mention the benefits and disadvantages of wearing a kilt.
Despite the lack of scientific evidence supporting his hypothesis, the author maintains that wearing a Scottish kilt in the traditional “regimental” way may have health-related benefits. He says kilt wearing is likely to produce an “ideal physiological scrotal environment” which is known to be beneficial for good sperm quality, although he says further research is needed.
This paper was not a systematic review of the evidence on kilts and male fertility. It seems to be heavily influenced by the author’s apparent fondness for kilts. The author did look for evidence linking kilts and male fertility, but found no direct, high quality evidence to support the theory of a causal link.
That said, men are usually advised to wear loose-fitting boxer shorts rather than tight-fitting Y-fronts or shorts, to help keep the testicles cooler and produce good quality sperm. Perhaps the author of this study should have thoroughly established the evidence for this first, before moving on to the optimum type of clothing for male fertility.
A final and worrying point, not related to male fertility, is the fact that the results of this entirely unsupported study were reported so uncritically by a major UK news website.