For decades, researchers have been exploring the possibility that vasectomy—a surgical method of birth control for men that blocks the tubes that carry sperm to the penis—may raise the odds for prostate cancer, the second leading cause of cancer death in American men.

Some studies have suggested a connection between vasectomy and prostate cancer, while others have not. This has led to conflicting media reports, confusion, and some lingering concerns.

However, two recent studies—both of them large—may offer some reassurance.  

If you've had this surgery, or are considering it, here's what you should know.

What the New Research Means

Both of the new studies found that men who have had a vasectomy are at no higher risk for prostate cancer.

One of the studies, conducted by the American Cancer Society and published in the Journal of Clinical Oncology, followed almost 364,000 men over age 40 for 30 years.

The study, the longest one conducted on the topic, found no increase in early stage prostate cancer in the approximately 42,000 men in the study who'd had a vasectomy.

It also found no heightened risk of aggressive prostate cancer or of dying from prostate cancer—a concern raised by some earlier research from the Harvard School of Public Health.

“While no single study is definitive, our research does provide some reassurance that a vasectomy is unlikely to meaningfully raise risk of developing or dying from prostate cancer,” says Eric Jacobs, Ph.D., strategic director of pharmacoepidemiology for the American Cancer Society, and lead author of the study.

A second study, which was published in BMJ, looked at health data on more than 326,000 Canadian men who had undergone a vasectomy, and the same number of men who hadn't had the surgery. 

This study also found no association between having a vasectomy and developing or dying from prostate cancer.

"These studies are both consistent, suggesting—as we all believe—that there is no relationship between vasectomy and prostate cancer risk or death from prostate cancer," says Stacy Loeb, M.D., assistant professor of urology and population health at NYU Langone Medical Center.

"It's a positive message and we should tell patients that this is not something that they should worry about."

Conflicting Research Over the Years

There have been more than 30 studies on vasectomy and prostate cancer conducted in the past 28 years, of differing sizes and quality.  

In 2012, after reviewing the research, the American Urological Association, or AUA, concluded that vasectomy likely didn’t increase prostate cancer risk—and that doctors didn't need to bring the issue up when discussing vasectomies with their patients.

But in 2014, a 24-year follow-up on 49,405 men from a Harvard School of Public Health study suggested otherwise. 

Its findings grabbed headlines because at the time, the study was the largest and longest of its kind.

The Harvard research found that men who'd undergone a vasectomy had a 22 percent higher risk for aggressive prostate cancer and a 19 percent higher risk for fatal prostate cancer.

The study did not, however, find a link between vasectomy and a higher risk of slow-growing prostate cancers or those that hadn't spread beyond the prostate.

Why some prior studies suggested an association between vasectomy and prostate cancer isn't clear.

But as Loeb points out, an association between two factors doesn't mean that one is the cause of the other.

What Now?

According to Marvin M. Lipman, M.D., Consumer Reports' chief medical adviser, a look at all the research that's been done on a possible link between vasectomy and prostate cancer "leaves us with the conclusion that the relationship between prostate cancer and vasectomy, is at most, tenuous, or more likely negligible."

And if concerns about an increased risk of prostate cancer have prompted you to decide against vasectomy, keep this in mind:

"Attempts at birth control in men by hormonal methods have all proved to be either impractical or unreliable," says Lipman. "The only sure method, and one that's devoid of effects on potency, has been and will likely continue to be, vasectomy."

"Meanwhile, if you're worried about your prostate cancer risk, focus on maintaining a healthy weight and, if you smoke, quit smoking,” he adds.