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21.04.2010

Cola bad for testes

Men who drink large amounts of cola produce fewer sperm, write Danish endocrinologists in the American Journal of Epidemiology. The Danes stumbled across the relationship by accident, while studying the effect of caffeine on male fertility.

Study
The researchers are part of a group of scientists who have been studying sperm production in men for many years. The group is headed by Shanna Swan and Niels Skakkebaek, who are also co-authors of this study. The theory that male fertility is in decline and that men are producing less and less testosterone is their brainchild. The researchers suspect that environmental pollution and hormones in meat [Hum Reprod. 2007 Jun;22(6):1497-502.] are the culprits, but they are also studying eating habits.

In this publication the Danes made use of data on 2554 young men who had applied to join the army, and had undergone a medical examination between 2001 and 2005. The researchers paid the men extra money for answering questions on their consumption of caffeine-containing drinks and producing a sperm sample.

Caffeine is an innocent stimulant, but many substances that interact with adrenergic receptors are not so good for the testes. Even a specific stimulant such as clenbuterol, which only interacts with the beta-2-adrenergic receptor, may cause deterioration in testes condition in animal studies. [Vet J. 2002 May;163(3):292-8.] That's why the Danes were interested to find out whether caffeine reduces men's fertility.

Results
The most important source of caffeine among these men was coffee. In second place came cola.

When the researchers counted the number of sperm cells in the samples, they saw that cola consumption reduced the sperm count. Heavy cola users, those who drank more than 7 litres of cola a week, produced 40-50 percent fewer sperm than men who drank no cola.

Cola did not have an effect on the sperm motility or quality.

Explanation
The researchers don't know how cola reduces sperm production. What they do know is that the negative effect is not caused by caffeine. Only in doses of more than 800 mg/day does caffeine have a negative effect on sperm quality. Cola doesn't actually contain much caffeine. So caffeine can't be the cause of the effect, the Danes reason.

It's possible that cola contains compounds that damage the testes, the Danes surmise, although they have no idea what these might be. Another possibility is that men who drink large amounts of cola lead less healthy lives.

Testosterone?
The Danes did not look at whether cola also reduces testosterone production.

Source:
Am J Epidemiol. 2010 Apr 15;171(8):883-91.

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