A case study of three active-duty service members who saw Navy doctors found their heavy use of pornography to be connected to erectile dysfunction and other sexual problems within their romantic relationships -- a finding the Navy is watching without comment, for now.

The independent study, undertaken by four San Diego-based naval health professionals, seeks to explain "sharp increases" in sexual difficulties among men under 40 in recent years and correlation with the prevalence of internet porn available for streaming, a technology that dates to 2006.

Published in the journal "Behavioral Sciences" in August, the study suggested health care providers need to more thoroughly take internet pornography use into account when diagnosing sexual problems, noting that some problems can be reversed simply by having a patient stop using pornography.

According to the report, diagnoses of erectile dysfunction in active-duty male service members more than doubled between 2004 and 2013.

"Future researchers will need to take into account the unique properties and impact of today's streaming Internet delivery of pornography," the study's authors wrote. "In addition, Internet pornography consumption during early adolescence, or before, may be a key variable."

One of the study's authors, Dr. Andrew Doan, head of the Addictions and Resilience Research department at Naval Medical Center San Diego, said in a statement that the study did not reflect the views of the center or of the Navy and declined to discuss the research more in-depth.

"Research on this topic is still underway by the authors," he said. "Therefore, it is too early to discuss this topic in open forum."

While multiple studies and reports have described the connection between pornography use and sexual and relationship problems, this may be the first to study active-duty service members on the topic. Doan said the study did not explore the effects of deployments, or other issues specific to the military, on the problem.

But his comments about the study's most significant finding suggest this is an issue that may be tied to mission readiness.

"Emotional health is linked to sexual health, directly affecting human resilience and service members' abilities to perform at their best," Doan said.

The three service members described in the case studies had previously seen doctors, two for problems including erectile dysfunction, low sexual desire and sexual difficulties with their partners, and one for mental health reasons. All three reported a trend of increasing internet pornography use, and two reported escalation to more extreme genres of internet porn.

In the first case, a 20-year-old enlisted service member, whose service branch was not identified, reported erectile dysfunction and inability to climax beginning during a six-month overseas deployment. When he returned, these persistent sexual issues began to cause problems in his relationship with his fiancee. When he cut back significantly on his internet porn use and stopped using a sex toy he had brought during his deployment, relations with his fiancee improved, and so did the relationship.

The second report described a 40-year-old service member with 17 years of service who had increased his use of internet pornography after his youngest child left for college and had begun to find his wife less stimulating than the online images. Care providers recommended he cut back on pornography use, but he found he couldn't. While he was referred to sex behavioral therapy, he declined to make an appointment, preferring to work the issues out on his own, according to the report.

In the third case, a 24-year-old junior enlisted sailor saw a doctor after attempting suicide by overdose. When his medical history was taken, he revealed he had spent more than five hours a day viewing online pornography over the last six months, and had noticed diminished interest in his wife during this time.

"When he became aware of his excessive use of pornography, he stopped viewing it completely, telling his interviewer he was afraid that if he viewed it to any extent he would find himself overusing it again," researchers wrote. "He reported that after he ceased using pornography his erectile dysfunction disappeared."

More study is needed, the authors wrote, to prove causation between internet pornography use and sexual difficulties by removing the variable of pornography and observing how study subjects respond.

Doan declined to comment on plans for future research, citing policy.

-- Hope Hodge Seck can be reached at hope.seck@military.com. Follow her on Twitter at@HopeSeck.