Dr. Narendra P. Singh, Unversity of Washington

"One of the best markers we have of the male biological clock is an increase in DNA-damaged sperm. At age 25, only 5 percent of a man's sperm has DNA damage; by age 35, that percentage has grown to 20 percent. That's a fourfold increase in just ten years. As the percentage of damaged sperm increases, the odds of fertilization decrease." — Narendra Singh, associate professor in the Department of Bioengineering at the University of Washington, Seattle

In a study examing the sperm of 66 men aged 22-80. Dr.Narendra P Singh, Dr. Charles Mueller, and Dr. Richard Berger found....

The researchers found that men over age 35 had sperm with lower motility and more highly damaged DNA in the form of DNA double-strand breaks. The older group also had fewer apoptotic cells -- an important discovery, Singh said.

"A really key factor that differentiates sperm from other cells in the body is that they do not repair their DNA damage," he said. "Most other cells do."

As a result, the only way to avoid passing sperm DNA damage to a child is for the damaged cells to undergo apoptosis, a process that the study indicates declines with age.

"So in older men, the sperm are accumulating more damage, and those severely damaged sperm are not being eliminated," Singh said. "That means some of that damage could be transmitted to the baby." More research is needed to determine just what the risks are......