Men with a certain type of infertility have a much higher risk of premature death, a sobering new study reveals.
Those who have no sperm in their semen - about 15 percent of male infertility cases - have an average death of 48.8 years old, according to data on more than 50,000 Danish men from 2006 to 2015.
Up until a few years ago, male fertility issues were lumped into one category, until research showed that there are three broad categories.
Lead researcher Dr Clara Helene Glazer said her team was stunned that this one category, known as azoospermia, carried such high mortality risks while the other categories didn't.
While there is nothing to show why this is the case, Dr Glazer said it may be due to underlying genetic factors.
'I was quite surprised that the azoospermic men had such a high risk,' Dr Glazer told DailyMail.com.
'The strongest hypothesis that the association between male infertility and mortality could be due to common underlying genetic factors.
'Certainly, more research is needed to identify interventions that could ultimately improve the health outcomes of these men.'
Dr Glazer, a medical doctor based in Copenhagen, started a PhD two years ago to find some answers about how male infertility influences, or is influenced by, general health.
Her first work showed male infertility was linked to higher risks of certain diseases, including heart disease and diabetes.
This study was to look further: what were the mortal impacts of that connection?
About one percent of men in the world are azoospermic, but among men with fertility issues it's not so uncommon - accounting for about one in six.
Azoospermia is characterized by a total lack of sperm in the man's semen.
The most common reason for this is a blockage in their anatomy that prevents sperm from entering the semen, known as obstructive azoospermia. Fewer have non-obstructive azoospermia, which is usually explained by genetic abnormalities with the testicles.
Oligospermia is a low sperm count which can be linked to various factors including restricted veins, sexually-transmitted infections, drug use, hormone imbalances, high BMI, exposure to chemicals - the list goes on.
Though the conditions are distinct, Dr Glazer said she presumed there would be a mortality risk for both men and women.