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By Maggie Fox, NBC News

Men who fail to produce sperm have a much higher risk of cancer than other men the same age – even other infertile men, researchers reported Thursday.

But all infertile men in the study had a somewhat higher risk of cancer than the general population, a finding that suggests the same genetic defects that cause infertility may also raise the risk of cancer, the researchers report in the journal Fertility and Sterility.

“There is evidence that infertility may be a barometer for men’s overall health,” says Dr. Michael Eisenberg, a urologist at Stanford Hospital & Clinics in California who led the study.

About 15 percent of U.S. men aged 15-45 are infertile, or a total of about 4 million men, the researchers say. And about 600,000 are azoospermic, meaning they do not make sperm, although they may produce semen, the fluid that carries sperm.

“An azoospermic man’s risk for developing cancer is similar to that for a typical man 10 years older,” Eisenberg said in a statement.

His team looked at the records of 2,238 Texas men who went into one infertility clinic between 1989 and 2009. About 450 of the men had azoospermia.

The researchers checked their medical records to see who later turned up in the Texas cancer registry, where most cases of cancer in the state are recorded.

Over an average of six years, 29 of the 2,238 infertile men developed cancer. That compares to 16.7 in an average Texas population of men the same age.

That gives the infertile men a 1.7 higher risk of cancer than the population as a whole.

When Eisenberg’s team looked at the men who had azoospermia, they found the rate was higher. They had nearly triple the risk of cancer compared to the general population. And those men diagnosed with azoospermia before age 30 were eight times as likely as other men the same age to get a cancer diagnosis over the next six years.

The men developed a wide range of cancer types, from brain tumors to stomach cancer, melanoma and prostate cancer. Luckily, the absolute risk of cancer was low. And as the men got older, the cancer risk grew lower.

The findings point to something genetic that causes both cancer and infertility, the researchers say. For example, defects in genes that repair damaged DNA can affect other functions of cells.

“Indeed, as up to 25 percent of the male genome is involved in reproduction, it is likely that other nonprocreative processes may also be affected by aberrations in fertility,” they wrote.

The researchers noted that the study is not perfect – it’s possible men who go to infertility clinics have better health care in general and were more likely to have cancer diagnosed early.They recommend doing more studies in larger groups of men.