Solitary confinement, even for just a few days, may significantly increase inmates’ risk of death after serving their sentences, new Cornell research shows.

The analysis of the Danish prison system found that 4.5% of former inmates who had spent time in solitary confinement – most for less than a week – died within five years of being released. That was 60% more than those who were not placed in solitary.

“That’s a significant increase in the risk of mortality,” said Christopher Wildeman, professor of policy analysis and management in the College of Human Ecology, and associate vice provost for the social sciences. “We think it’s a pretty substantial effect.”

Wildeman and co-author Lars Andersen – both researchers at the Rockwool Foundation Research Unit in Copenhagen, which funded the study – published their findings Feb. 4 in The Lancet Public Health.

Most research on solitary confinement has focused on placements of months or even years at prisons holding the most serious offenders, Wildeman said. The new study tracked everyone – nearly 14,000 people – who began and ended sentences in Danish prisons or jails over a five-year period between 2006 and 2011.

Of the nearly 1,700 inmates who experienced solitary confinement, the average total stay was nearly nine days, but half spent fewer than five days and two-thirds less than a week.

Understanding the effects of such short exposures is important, Wildeman said, because they are often avoidable.

“For somebody who is in disciplinary segregation for 72 hours because of a specific infraction, there’s almost always an alternative that a warden or guard could use that wouldn’t involve putting someone in solitary,” he said.

Alternatives might include a fine, loss of privileges or short increase in sentence length, Wildeman said.

The researchers had access to a wealth of data about the former inmates from Danish government registers – not only age, gender, race, ethnicity and education levels, but also information about their family backgrounds, employment and housing histories and prior contacts with the criminal justice system.

That allowed the study to account for many factors that might have made someone more likely to end up in solitary confinement or to die after being released, while acknowledging some gaps in data concerning potential mental health or addiction issues.

“We were able to adjust for a vast array of characteristics across a number of domains,” Wildeman said, “to make us feel like this is a potentially causal relationship.”

Government registers also confirmed dates and causes of death within five years of release. The study determined that the higher death rates for those who had experienced solitary confinement – generally younger inmates serving longer sentences – was driven primarily by non-natural causes such as accidents, suicides and violence.

Research has shown that the extreme isolation imposed by solitary confinement has “often devastating psychological consequences,” the article notes. In addition, Wildeman said, disciplinary segregation may disrupt job training or educational programming, and lead inmates to be branded as problems, potentially influencing their behavior.

The finding that just a day or two in solitary confinement appears linked to a higher risk of death after release is somewhat surprising, Wildeman said. More research is needed to understand exactly what amount of exposure elevates mortality, he said.

While not saying definitively how the findings from Denmark translate to other countries, the researchers noted previous studies suggest that incarceration there and in other European nations “has much the same consequences” as in the United States.

The use of solitary confinement, the authors assert, should be viewed not only as an ethical issue but as a public health concern. Former inmates who have logged time in solitary confinement represent “a vulnerable population in need of interventions,” they concluded, highlighting the need for careful evaluation of the costs and benefits of even short placements in solitary.

“The core intervention that you would want the correctional system to try first,” Wildeman said, “is any sanction other than solitary confinement.”