A study of 2,554 young Danish men found that young men who drink lots of cola have lower sperm quality and have a large decrease in sperm concentration.
According to the American Journal of Epidemiology, however, these results are still quite difficult to interpret clearly.
A team of researchers in Copenhagen focused on the effects of daily caffeine consumption on male fertility.
Between 2001 and 2006, more than 2,000 18-year old young men were questioned about their habits and lifestyle, in addition to providing a semen sample and a blood test.
It was found that moderate consumption of cola has no effect on sperm quality. But if young people drink more than one litre per day, sperm concentration is less.
Researchers do not believe that this is only due to the effects of caffeine in cola; other factors such as stress or physical activity may play a role in this phenomenon.
They also found that these young cola lovers drank less milk and ate less fruit, vegetables and fish. They also drank more alcohol and smoked more. This could also influence the results.