Consuming large volumes of soft drinks may lower mens' sperm count, suggest the results of a new Danish study. Professor Tina Kold Jensen and colleagues, at the University Department of Growth and Reproduction at the Rigshospitalet in Copenhagen, found that men who consumed 'high levels' of cola and/or caffeine had reduced sperm concentration and a lower total sperm count, although only the result for cola intake was 'significant'.

Additionally, the cola drinkers tended to eat more fast foods and less fruit and vegetables, so the researchers were careful to point out that the findings could also be attributed to a less healthy lifestyle or poorer overall diet in general among these men. 'It's important to note that the men who drank a lot of cola were also different in many other ways', Professor Kold Jensen told Reuters Health.

To investigate the association between caffeine intake and semen quality, the authors collected semen samples from 2,554 young Danish men between 2001 and 2005, while they were undergoing fitness examinations prior to military service. The participants were asked to complete a questionnaire about lifestyle and dietary habits, which included information about the amount of caffeine consumed from various sources.

While low to moderate caffeine or cola intake was not found to be associated with semen quality, those who consumed more than 14 half- litre bottles of cola per week had almost 30 per cent fewer sperm than the non-cola drinkers. The reduction was unlikely to be due to caffeine, however, as the effect of tea or coffee consumption was less pronounced, despite these having a higher caffeine content. The findings were published in the American Journal of Epidemiology.

It is not clear whether the other ingredients in cola, the unhealthy lifestyle, or a combination of factors is to blame, but the authors said they could not 'exclude the possibility of a threshold above which cola, and possibly caffeine, negatively affects semen quality'.

Until now, studies examining the effect of caffeine on male reproductive health have produced unclear and conflicting results. Professor Kold Jensen explained that the selection of previous participants was usually based on whether they were infertile or about to undergo a vasectomy. Although the low sperm levels found in the current study were still within the World Health Organisation's reported normal limits, reduced sperm quality could potentially lead to infertility.