Parents often don't lock up or unload guns, even when kids have mental illness: Study

— -- Among parents who own guns, only one in three store their guns the way pediatricians recommend, a new study found: locked, unloaded and separate from ammunition.

This was the case whether or not the children in the home had any history of mental health issues, according to the study in the journal Pediatrics.

Guns that are unlocked and loaded, the lead author of the study Dr. Matthew Miller said, may be more dangerous to the children than to anyone else, including kids at risk of harming themselves.

"One of the most incontrovertible pieces of evidence is that when a gun is in the home it increases risk of suicide," Miller, a professor of health sciences and epidemiology at Northwestern University, told ABC News, especially when left unlocked and loaded.

The Centers for Disease Control and Prevention said in their mortality data report that, among children age 10 to 17, firearms accounted for more than 40 percent of all suicides.

Mental health conditions increase the likelihood of suicidal behavior, so Miller, who has researched gun violence for the past 20 years, and his team decided to study guns and homes with children who have a history of mental health challenges.

Attention deficit hyperactivity disorder (ADHD) or attention-deficit disorder (ADD), depression and mental health conditions other than depression were categorized as "self-harm risk factors" in this study.

The research team asked two crucial questions for the study:

Are parents whose children are at risk of self-harm any less, or more, likely to live in homes with guns? Do parents with firearms store their household guns more, or less, safely?

Researchers conducted an online survey of almost 4,000 adults across the United States in 2015. The results were self-reported and the authors admit that this could increase the chance of bias, but said they do not believe it played a dominant role in their findings.

Among the group who responded, approximately one in three households contained firearms.

Of those, having a child with self-harm risk factors did not affect how parents stored their guns. This came as "no surprise" to Miller.

Despite what appears to be a recent upswing in gun violence, and extensive media coverage of school shootings, public health recommendations regarding homes with both guns and children have not wavered.

The American Academy of Pediatrics recognized the need to reduce firearm injury to children over a quarter of a century ago. They say the safest home for a child is one without guns. But if guns are in the home, their recommendation is that risk can be substantially reduced by storing all household firearms locked, unloaded, and separate from ammunition.

"The best thing to do is to not have a gun in the home, especially if you have a child with a mental health issue," Miller advises parents. "But even if your child does not have a mental health issue, children can be impulsive."

In either case, the study showed that having a gun in the home can increases the risk of a child dying by suicide.

Jay-Sheree Allen, M.D. is a resident in the ABC News Medical Unit.