Tina Kold Jensen, Professor at the University Department of Growth and Reproduction at the Rigshospitalet, Copenhagen and the leading author of the study, said that previous studies did not give a clear answer on whether caffeine affects male fertility. The new research included 2,554 men from Denmark, who were enrolled in the study between 2001 to 2005. The participants had to fill in a survey about their diet and lifestyle, including their consumption of caffeine from different sources. Scientists also examined sperm quality, using the participant's semen samples.
The results of the study showed that men with high intake of caffeine and cola, which is more than 800 mg a day or more than 14 liter bottles of cola a week, had low sperm count and concentration. Men, who drank caffeine moderately, had normal sperm count and concentration.
The study did not reveal if caffeine in coffee or tea affects sperm count. Scientists say that it can be the ingredients in soft drinks, including cola or unhealthy lifestyle of men, who drink soft drinks in excess that led to low sperm count.
The findings of the study are published in the American Journal of Epidemiology.