Having a vasectomy doesn't increase a man's risk of developing prostate cancer or dying from it, a U.S. study suggests.
Previous research has been mixed about the risk of prostate cancer associated with vasectomy, a common form of long-term birth control that involves snipping or blocking tubes that transport sperm out of the testicles.
"Our study provides some reassurance that having a vasectomy is unlikely to meaningfully increase risk of developing any type of prostate cancer, including fatal prostate cancer," said lead study author Eric Jacobs, a researcher at the American Cancer Society in Atlanta.
Two things that do make prostate cancer more likely are smoking and obesity, Jacobs said by email.
"Men who want to lower their risk of fatal prostate cancer should focus on maintaining a healthy weight and, if they smoke, quitting smoking," Jacobs said.
Prostate cancer is the second most common type of malignancy among men in the U.S., behind melanoma.
While vasectomy isn't the primary form of birth control for most couples, about 5 percent of women of reproductive age in the U.S. say this is the method they use to prevent pregnancy, according to the Centers for Disease Control and Prevention.
Men who undergo this sterilization procedure often worry about whether it will negatively impact their sex life or fail to prevent pregnancy.
Concerns about a cancer risk spiked after a large 2014 study linked vasectomies to a 10 percent greater risk of developing prostate tumors, as well as a 20 percent higher risk of fatal prostate cancer, Jacobs and colleagues note in the Journal of Clinical Oncology.
But the overall risk of prostate cancer is still quite low, said Jennifer Rider, a public health researcher at Boston University and Harvard University who was an author on the 2014 study.
"Even a 20 percent increase in the risk of lethal disease - if that is in fact the true relative risk - is still quite small in absolute terms," Rider said by email. "Given that the benefits of vasectomy as an effective method of birth control are well established, vasectomy remains an important contraceptive option."
For the current study, researchers examined data on almost 364,000 men who were at least 40 years old when they joined a large cancer prevention study in 1982, including 42,000 men who'd had vasectomies.
Over 30 years of follow-up, 7,400 men died of prostate cancer.
Overall, men with a vasectomy had a 1 percent higher risk of dying from prostate cancer - a difference too small to rule out that it was due to chance.
When men did develop prostate cancer, those with vasectomy were 9 percent less likely to have lethal "high-grade" cancers, though this difference was also statistically insignificant.
One limitation of the study was that vasectomy status was reported by men's wives, potentially resulting in some under-reporting, the authors note. Researchers also lacked data on vasectomies performed after the start of the study.
In this study, as well as in the 2014 research, it's possible that men who had vasectomies were screened more often for prostate cancer or that they were different in some ways from their peers who didn't get the sterilization surgery, noted Siobhan Sutcliffe, a public health researcher at Washington University School of Medicine in St. Louis who wasn't involved in either study.
"Another possible explanation for the difference in study findings is chance," Sutcliffe said by email. "This is why we investigate associations in many different study populations so that we can ultimately draw conclusions from a large body of evidence rather than from one study."