Suicide rates for U.S. soldiers on active duty rose in America's “endless” wars in Vietnam, Iraq and Afghanistan, reversing historical trends that go as far back as the Civil War, a study published Friday found.

The study in JAMA Network Open also suggested there is no clear link between combat operations and military suicide.

Researchers from the University of Hawaii and the DOD analyzed military records as far back as the 1840s to develop what they say is the most extensive historical examinations of suicide among active-duty soldiers to date.

“Rising suicide rates during wartime seems to be a new trend that only appears in America’s modern so-called ‘endless’ wars in Vietnam, Iraq and Afghanistan,”Jeffrey Smith, the lead researcher on the study at the University of Hawaii, said. “Thus, history suggests that combat itself does not drive suicide rates up, but instead possibly serves to suppress suicide rates.”

“The paradigm has most definitely shifted,” he added.

Rates steadily increased from about five suicides per 100,000 soldiers during World War II to about 27 per 100,000 soldiers in the Afghanistan and Iraq wars. In between wars, the rate would usually stand at about 10 suicides per 100,000 soldiers, the study reported. At the beginning of each war they noticed a drop in suicide, but once the conflict dragged on, suicides began to rise, Smith said.

“The findings of this study suggest that factors away from the battlefield may be associated with the change in suicide rates during active combat and among personnel in the U.S. Army,” the study concluded.

Researchers for the study say one limitation was how the Army defined active-duty service members, for example, the definition likely included militia members in the 19th century and some reservists. “Nevertheless, the study focused on tracking suicide rates for active-duty service members in the U.S. Army, however the military chose to define them,” they wrote.

Retired Army Col. Carl Castro, who previously oversaw DOD-funded suicide research and has not yet seen the study, cautioned against comparing historical data to current data because of the possibility of documentation errors associated with the stigma around suicide.

He also questioned whether the nature of the wars in Afghanistan, Iraq and Vietnam — considering their length, geopolitical context, and target — had any unique impact.

“The repetitive nature of war just exacerbates everything but it doesn’t change the fundamental nature of war,” Castro said. “Suicide is an individual-level phenomenon.”

NBC News reached out to the U.S. Army for comment and a spokesperson pointed to the DOD’s annual report on suicide released in September. A summary of that report states that several studies have shown being deployed is “not associated with suicide risk among serivce members.” The report also showed that suicide rates among the active-duty component of the military has risen over the last five years, a trend they said was similar to that of the national population.

These findings come almost a week after The Washington Post reported that a trove of government documents appears to have purposely misled the public about the Afghanistan War.

The suicide rate among veterans has also continously grown since 2005, according to the Department of Veterans’ Affairs latest annual suicide prevention report.

“We still do not know what the chronic, long-term factors are as opposed to the short-term, acute ones that drive military suicide. We need to consider broader socioeconomic factors and trends,” Smith said. The next step for his team is taking is to examine these factors, which include psychological well-being, happiness, loneliness and level of income, among others.

“Access to additional historical and stratified medical data from all branches of the U.S. military could prove very helpful in identifying the different trends in suicide rates between the branches,” he added.

If you or someone you know is in crisis, call the National Suicide Prevention Lifeline at 800-273-8255, text HOME to 741741 or visit SpeakingOfSuicide.com/resources for additional resources.