Writing in the American Journal of Epidemiology, scientists reported on possible links between caffeine and cola intake on the one hand and low fertility on the other.
The researchers used data on fertility and soft drink consumption among 2,554 young Danish men recruited when they were examined to determine their fitness for military service in 2001–2005.
The results of the survey suggested that moderate caffeine and cola intake is not associated with reduced semen quality but that there may be a link at high consumption levels.
Cola consumption of more than 14 half-litre bottles a week and/or caffeine intake over 800mg a day was associated with reduced sperm concentration and a lower total sperm count.
However, the results were only significant for cola. The scientists observed an apparent threshold of around one litre a day above which cola consumption began to be associated with a reduction in semen quality.
Because the caffeine content of cola is not high, the scientists concluded that poor semen quality may be attributed to constituents in cola other than caffeine.
Summing up their findings, they said: “We cannot exclude the possibility of a threshold above which cola (and possibly caffeine) negatively affects semen quality.
“Alternatively, a less healthy lifestyle among these men may explain the findings. Since cola consumption is high and has been increasing among young Danes, our findings, if confirmed, may be of public health concern.”
Source: American Journal of Epidemiology
Published online ahead of print: doi:10.1093/aje/kwq007
Caffeine Intake and Semen Quality in a Population of 2,554 Young Danish Men
Authors: T.K. Jensen, S. H. Swan, N. E. Skakkebæk, S. Rasmussen and N. Jørgensen