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In the largest-ever study of its kind, researchers looked at secondhand” exposure to handguns among 9.5 million Californians over a 12-year period

Women who do not own guns but live with adults who do are significantly more likely to die by suicide compared with their female neighbors in gun-free homes, new research led by scientists at Northeastern and Stanford Universities shows.

The study, published in JAMA Psychiatry, is among the largest ever to explore the risk of a gun in the home. Smaller previous studies clearly show that a gun in the home increases the risk of suicide for people who live there, but haven’t isolated the risks for non-gun owners. In this study, the researchers were able to sort gun-owners from non-gun owners and estimate what happens to the risk of dying by suicide for a woman in that situation. 

It’s analogous to tobacco, in the way we think about secondhand risks from smoking differently than the risks smokers themselves face by choosing to smoke,” said the lead author of the study Matthew Miller, MD, ScD, a professor of epidemiology at Northeastern University. The question we tried to address is what happens to a woman’s suicide risk when someone she lives with brings a handgun into their gun-free home for the first time. The answer: her chances of dying by suicide increase by more than 40%.”

One previous study quantified the risks faced by individuals who do not own guns but live with others who do — but it was conducted 25 years ago and examined too few deaths to reach clear conclusions.

Despite widespread perceptions that a gun in the home makes its inhabitants safer, rigorous studies have been nearly unanimous in finding that people who live in homes with guns are at higher risk of dying violent deaths, whether by homicide, suicide, or in accidents,” said co-author David Studdert, LLB, ScD, a professor of health policy in the Stanford University School of Medicine’s Department of Health Policy and a professor of law at Stanford Law. But homes don’t own guns; people do. And sorting out exactly who in these homes faces elevated risks and estimating the size of those risks is vitally important.”

In the largest cohort study ever assembled to estimate the secondhand suicide risk imposed by household firearms, the research team followed 9.5 million women living in California aged 18 and older. None of them owned handguns and all started out living with at least one other adult in a handgun free household. Over the ensuing 12 years, October 2004 through December 2016, over 330,000 began living with handgun owners because someone they lived with lawfully became a new handgun owner.

An earlier study by the research team found that women who personally own handguns were seven times more likely to die by suicides than women who don’t own handguns.

We were particularly interested in the extent to which gun suicides increased and if there was a corresponding decrease in suicide by other means,” said Yifan Zhang, PhD, a research scholar in the Department of Health Policy at Stanford and study co-author. Our findings mirror the pattern from our previous study: There isn’t much substitution so the overall suicide risk increases substantially.”

The other co-authors of the study were Erin E. Holsinger, MD; Lea Prince, PhD; Sonja Swanson, ScD; and Garen J. Wintemute, MD, MPH. The study was funded by the National Collaborative on Gun Violence Research and the Joyce Foundation. Stanford Law School, and the Stanford University School of Medicine supported assembly of the cohort used in the study.