Dr. Con Mallidis of Queen's University, in Belfast, Northern Ireland, said the increase in the numbers of diabetics diagnosed at a young age has coincided with worldwide concerns over male fertility.

"This is not simply a coincidence," Mallidis told the 24th annual conference of the European Society of Human Reproduction and Embryology in Barcelona, Spain. "We have shown for the first time that diabetes adversely influences male fertility at a molecular level."

The scientists studied semen samples from men with diabetes who had been receiving insulin therapy. On initial routine microscopic examination the semen samples appeared normal, apart from a slight decrease in volume.

"But when we looked for DNA damage, we saw a very different picture," Mallidis said. "Sperm RNA was significantly altered, and many of the changes we observed are in RNA transcripts involved in DNA repair. And comparison with a database of men of proven fertility confirmed our findings."

Diabetics have a significant decrease in their ability to repair sperm DNA, and once this is damaged it cannot be restored, Mallidis said.