Vasectomies may be a safe choice for avoiding unplanned pregnancies, but new research shows the procedure could also lead to a 10 percent increase in the risk of developing a serious form of prostate cancer.

Researchers at the Harvard School of Public Health found that the risk was worse if men had the procedure done before the age of 38. These men incurred a 20 percent increased risk of developing prostate cancer.

Behind only lung cancer, prostate cancer is the second leading cause of cancer death in men in the United States. According to the American Cancer Society, nearly 30,000 men will die of prostate cancer during the year 2014. About 233,000 new cases will be diagnosed.

The researchers drew the study’s results from the medical records of nearly 50,000 men. One in four of these men had a vasectomy. Researchers aren’t sure why a vasectomy would increase the risk of prostate cancer. They guess the procedure changes the protein composition of semen, which is made in the prostate.

In a vasectomy, the vas deferens — the vessel leading from each testicle and eventually through the prostate gland — is cut, clamped or otherwise obstructed. It no longer carries sperm to be mixed with seminal fluid.

Because the most deadly forms of prostate cancer are rare, the increase in risk for lethal forms of the disease was small. But the researchers say more study is needed to determine what exactly underlies the increase in risk. They also said the procedure appeared to have no effect on developing less dangerous forms of prostate cancer.

More study is needed and the current findings don’t mean vasectomy is a bad option for men. But if you have concerns, talk to your urologist before scheduling the procedure.