UK scientists have discovered that DNA damage in the sperm of diabetic men is higher than in the sperm of men who do not have diabetes. They suggest this may make diabetic men less fertile.

You can read about the study in the journal Human Reproduction.

The researchers, led by Dr Ishola Agbaje, a research fellow in the Reproductive Medicine Research Group at Queen's University, Belfast, compared the quality of the sperm from diabetic men with non-diabetic men by examining nuclear and mitochondrial DNA (MtDNA) .

The participants were 27 diabetic men whose average age was 34 and 29 non-diabetic men whose average age was 33.

The results showed that:

-- Semen volume was lower in diabetic men compared with non-diabetic men (2.6 and 3.3 ml respectively).
-- But sperm concentration was not significantly different between the two groups.
-- Total sperm output, form, structure and "motility" (ability to move) were also largely the same in the diabetic and non-diabetic men.
-- The nuclear DNA in diabetic men's sperm cells was more fragmented than that of the non-diabetic men (52 per cent versus 32 per cent).
-- There were more deletions in the mitochondrial DNA of diabetic men's sperm cells than those of the non-diabetic men.
-- The mitochondrial DNA deletions in the diabetic men's sperm cells ranged from 3 to 6 and averaged 4, while for the non-diabetic men it ranged from 1 to 4 and averaged 3.

The study concluded that:

"Diabetes is associated with increased sperm nuclear and mtDNA damage that may impair the reproductive capability of these men."

Deletions and fragmentation of DNA results in loss of genetic material which, in the case of nuclear DNA, causes infertility as the sperm is not able to deliver its full complement of genetic codes in fusion with the egg to create a viable embryo.

Mitochondrial DNA (MtDNA) is found in mitochondria -- tiny "power-stations" inside cells that make energy to fuel cell activity.

In humans and many other organisms, sperm cell mitochondria are destroyed when the sperm's nuclear DNA combines with the egg's nuclear DNA and only the egg's mitochondria go on to survive in the new individual.

A number of studies have suggested that high levels of mtDNA deletions in sperm cells is linked to lower fertility in men.

Dr Agbaje said:

"As far as we know, this is the first report of the quality of DNA in the nucleus and mitochondria of sperm in diabetes. Our study identifies important evidence of increased DNA fragmentation of nuclear DNA and mitochondrial DNA deletions in sperm from diabetic men. "

"These findings cause concern, as they may have implications for fertility," he added.

Type 1 and Type 2 diabetes are on the increase throughout the world, with the latter increasingly being described as a "modern disease" caused by lifestyle, diet and obesity. Type 1 diabetes is usually diagnosed in younger people and is also increasing at the rate of 3 per cent a year in European youngsters.

The reason for the increase in Type 1 diabetes is not known, but some scientists are suggesting that genetic factors could be involved, or that viruses could trigger the onset of the disease.

Dr Agbaje suggested that:

"If the increasing trend in the incidence of type I diabetes continues, this will result in a 50% increase over the next ten years. As a consequence, diabetes will affect many more men prior to and during their reproductive years."

"Infertility is already a major health problem in both the developed and developing world, with up to one in six couples requiring specialist investigation or treatment in order to conceive," he added.

The researchers point out that semen quality has been declining over the last 50 years and poor sperm is thought to cause infertility in 40 to 50 per cent of infertile couples.

"The increasing incidence of systemic diseases such as diabetes may further exacerbate this decline in male fertility. However, it is not clear to what extent clinics consider information about the diabetic status of their patients when investigating fertility problems," said Dr Agbaje.

Scientific director of the Reproductive Medicine Research Group and study co-author, Professor Sheena Lewis, said:

"Our study shows increased levels of sperm DNA damage in diabetic men. From a clinical perspective this is important, particularly given the overwhelming evidence that sperm DNA damage impairs male fertility and reproductive health."

"Other studies have already shown that, while the female egg has a limited ability to repair damaged sperm DNA, fragmentation beyond this threshold may result in increased rates of embryonic failure and pregnancy loss. In the context of spontaneous conception, sperm DNA quality has been found to be poorer in couples with a history of miscarriages," she explained.

However, Prof Lewis pointed out the limitations of a small study like this one, which can only highlight a possible concern and point the way to further research.

And she concluded that this study strongly suggests there is a need to monitor the situation:

"Given the global rise in the prevalence of diabetes, it is also vital to examine the reproductive outcomes of pregnancies fathered by diabetic men, and the prevalence of diabetes amongst men attending for infertility treatment."