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The comet effect.
Healthy DNA in male sperm nuclei resembles bright stars, while defective DNA looks more diffuse and appears to trail cometlike tails.

Sheena Lewis

Sugar and Sperm Don't Mix

Add infertility to the lengthy list of medical problems associated with diabetes. The first research to examine the relationship between the disease and reproductive health suggests that diabetic men carry a much higher percentage of sperm with damaged DNA than do their healthy counterparts.

The World Health Organization projects that the number of people with diabetes will nearly double by 2025, surpassing 300 million, due partly to an increasingly obese, inactive, and aging population. Type 1 diabetes typically manifests itself in childhood or young adulthood, while Type 2 usually strikes adults over 30. Both forms of diabetes can lead to heart and kidney disease, nerve damage, and blindness. They also can cause erectile and ejaculatory dysfunction and reduce semen quantities. But no one had investigated the disease's impact on sperm quality.

Researchers at Queen's University in Belfast, U.K., analyzed semen samples from two small groups of young men attending a local fertility clinic. The first group included 27 patients with Type 1 diabetes, and the second comprised 29 nondiabetics of similar age. In today's online issue of Human Reproduction, the team reports no significant difference in the sperm concentration, appearance, or mobility between the two groups. But when the researchers performed DNA analyses, they found that 52% of sperm from diabetic men contained fragmented DNA, which could prevent them from fertilizing an egg or lead to abnormalities in the offspring. Only 32% of sperm had defective DNA in the control group.

The problem could result from destructive free radicals, which surge in diabetics because of high blood-sugar levels. "We know that sperm is very susceptible to free radical damage," says reproductive biologist and co-author Sheena Lewis. Because the DNA in sperm has no repair mechanisms, she adds, the damage is permanent. Lewis says the team's unpublished results show the same effect in men with Type 2 diabetes. To confirm the findings, Lewis plans to look at the prevalence of diabetic men who are seeking treatment in fertility clinics. Researchers should also track whether birth defects are more prevalent in children of diabetic fathers, she says.

The study represents "a good start," but much more needs to be learned, says reproductive endocrinologist Pasquale Patrizio of the Yale Fertility Center in New Haven, Connecticut. In particular, he says, it's important to know how long the individual subjects have been afflicted with diabetes because that could impact the amount of damage to sperm DNA. Likewise, Patrizio says, the blood sugar of the diabetic men in the study was not controlled, so it raises the question of whether fertility could be improved by better disease management.

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