The study written by Lubomira Tothova et al., but not reported in the news until now, was published in the December issue of the journal Food and Chemical Toxicology.
The scientists said their findings conflict with their own 2010 study (Celec & Behuliak) where rats drank as much Coke as they liked for three months; these results showed slight increases in testosterone and estradiol (another sex hormone) in plasma compared with rodents that drank water.
This time around 50 rats were divided into a water-drinking control group (10 animals) then equivalent groups drinking as much Coca-Cola, Coca-Cola Caffeine-Free, Coca-Cola Light and Coca-Cola Zero as they liked.
No negative effects on testicular tissue
The animals were killed after the experiment, and Tothova et al. measured the oxidative status of testicular tissue and plasma testosterone, finding no significant differences between groups.
“Consumption of different types of Coca-Cola beverages for six months instead of water did not induce any negative effects on rat testicular tissue in terms of increased oxidative and carbonyl stress or decreased anti-oxidative status,” Tothova et al. write.
“Similarly, neither plasma nor testicular testosterone concentrations were different, suggesting that drinking Coca-Cola beverages for six months does not alter the endocrine function of testes in adult rats.”
Future studies will examine if there is an effect on spermatogenesis and fertility, Tothova et al. write, before adding: “However, based on our results, we suggest there is none.”
Despite hypothesizing that glucose/fructose, caffeine and artificial sweeteners in Coca-Cola drinks would cause oxidative and carbonyl damage to rat testes, the team found this was not the case in the current study.
“However, it remains unclear whether a longer study with more animals per group would uncover a significant effect of Coca-Cola beverages on testosterone production,” Tothova et al. write.
“It could be hypothesized that at least the groups drinking caffeine-containing Coca-Cola beverages could have significantly altered testosterone concentrations,” they add.
Few studies on Coke's 'possible harmful effects' on male reproductive organs
Why is this study significant? Introducing their work, Tothova et al. say that only a few studies have examined the possible harmful effects of Coca-Cola branded beverages on male reproductive organs.
They cite “controversial studies” including Umpierre et al (1985), who observed reduced sperm movement after one minute’s incubation with different Coca-Cola drinks, with the effect mainly linked to a low pH.
“But since different formulations of Coca-Cola showed different action, the authors stated that the ‘secret formula’ could also play a role as a co-factor,” Tothova et al. write.
Rats prefer Red Coke, followed by Coke Zero...
Since the 1985 study and one other relevant study (Hong et al. 1987) were in vitro, the scientists set out to examine possible effects of Coca-Cola on the oxidative status of testicular tissue and its endocrine function, starting with their three-month in vivo study and moving on to the current research.
Interestingly, the rats in the standard Coca-Cola group drank far more on a daily basis (150ml+) than any other variety. Coke Zero, circa. 60ml/day was the closest rival, followed by water, Coca-Cola Light and Coca-Cola Caffeine Free respectively, which rats drank circa. 50ml/day of on average.
(Rat Photo: Jeffrey Goldsmith/Flickr)
Title: ‘No harmful effect of different Coca-Cola beverages after 6 months of intake on rat testes’
Authors: Tothova, L., Hodosy, J., Mettenburg, K., Fabryova, H., Wagnerova, A., Babickova, J., Okuliarova, M., Zeman, M., Celec, P.
Source: Food and Chemical Toxicology, Vol.62, December 2013, pp.343-348