A study of over 2,500 Danish 18-year old men suggests that heavy cola drinking may lower sperm production.
Men who drank a liter or more of cola daily had a sperm count of about 3,500 per milliliter, compared with 5,000 per liter for those who didn't drink cola. While both of these sperm counts fall within the normal range, men with lower sperm counts have a higher risk of being infertile.
This effect doesn't seem to be due to caffeine, since it wasn't seen in heavy drinkers of coffee or tea.
The cola drinkers showed many differences from the rest of the men in the study. Notably, they ate a lot more fast food and a lot less fruits and vegetables.
The study was performed between 2001 and 2006. All men in Denmark are required to undergo a compulsory physical examination when they turn 18, to determine their fitness for military service. At this time, the study subjects also completed a detailed questionnaire about lifestyle factors, including diet.
The study was originally undertaken to test the effect of caffeine on sperm quality and quantity. The researchers were also interested in cola consumption because it has been on the increase, particularly among the young, in recent years. The study did find that high caffeine consumption was related to a small decrease in sperm count, but the decrease was statistically insignificant.
The research was published in the April 15, 2010 issue of the American Journal of Epidemiology.