May 6, 2022

By Tom Insel, MD, and Matthew Hirschtritt, MD, MPH

Good morning, Research Roundup readers. This week, we discuss provocative research that finds women in homes with firearms are four times more likely to die by suicide than those in homes without them. We explore the neuroscience of touch and a discovery of the long-sought neural messenger for the pleasurable sensations we get from cuddles and caresses. Plus, a look at new research on eating disorder symptoms among LGBT adults. Read on!

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Guns in the Home Increase the Suicide Risk for Women

Somewhere between 39% and 46% of Americans live with a firearm, a common household item that comes with serious risk. According to data summarized by The Educational Fund to Stop Gun Violence, firearms are involved in about half of all suicide deaths. On average, 64 Americans die by firearm suicide daily. Firearms are highly lethal: nearly 90% of firearm suicide attempts are successful. Many people purchase firearms to protect themselves and their loved ones, but the rate of firearm suicide is nearly double the rate of firearm homicide.

Does having a firearm at home increase the risk of firearm suicide? Data from multiple studies show that people living in households with a firearm are about three times more likely to die by suicide compared with people who live in firearm-free homes. But the proportion of those deaths attributed specifically to firearms is less clear.

Image: Shutterstock

Matthew Miller of Northeastern University and the Harvard T. H. Chan School of Public Health addressed this crucial question by examining rates of suicide (by any method) and firearm suicide among women living in homes in which someone else owned a firearm. The researchers used data from 9.5 million women in California in the longitudinal LongSHOT cohort between 2004 and 2016. None of the women owned a firearm, and at the beginning of the study, no one they lived with owned a firearm.

Over the approximately 12-year observation period, 3.5% of the women ended up living with a firearm owner. Compared with women in firearm-free homes, women in homes with a firearm were about 40% more likely to die from suicide by any method. They were more than four times more likely to die of firearm suicide than women in firearm-free homes.

These data paint a grim picture of household firearm ownership. Not only are firearms potentially deadly for owners, but also for those who have access to them in the house. At the very least, this study should motivate clinicians to routinely ask their patients about firearm access and provide advice about how to safely store them.

Suicide Deaths Among Women in California Living With Handgun Owners vs Those Living With Other Adults in Handgun-Free Homes, 2004-2016 JAMA Psychiatry, April 27, 2022.

Matthew Hirschtritt

Caressed by a neurotransmitter

Egoreichenkov Evgenii/Shutterstock

The neuroscience of touch has been a rich area of research. Scientists have identified the specific pathways for telling us when something hurts or itches, insights that have helped guide the search for treatments. Researchers have also started to better understand how – and why – things feel good: Neurons called C- tactile fibers that innervate our skin carry sensations from caresses and cuddles, positive social information that is critical for bonding.

New research in mice from Benlong Liu and colleagues at Washington University School of Medicine in St. Louis has identified the long-sought messenger for these pleasurable sensations: Prokinecticin-2 (PROK-2). This neurotransmitter appears to be the key for delivering the sensations of pleasurable touch, doing so through a prokinecticin-2 receptor (PROKR-2) in the spinal cord – one that also carries information about social grooming. Mice genetically altered to lack the receptor for PROK2 show normal responses to painful or itchy stimulation, but they appear indifferent to grooming or pleasant touch. These same mice show profound changes in their stress responses and social behavior when they grow up.

The neuropeptides oxytocin and vasopressin have long been associated with mediating social behaviors, such as maternal care and social bonding, by activating pathways in the brain. This new research shows that social experiences, including grooming and cuddling, are processed before reaching the brain. While there is always a risk extrapolating from mice to humans, the physiological activity of PROK2 fibers in mice look remarkably similar to C-tactile fibers that carry positive social information in humans. 

The authors speculate that a deficiency of PROK2-PROKR2 signaling in humans could hamper social and emotional bonding, which in turn could lead to social isolation, anxiety, and mental disorders. Just as a better understanding of the pain pathways may lead to new treatments, the authors suggest further research might reveal mechanisms “by which pleasant touch deprivation contributes to social avoidance behavior and mental disorders” – insights that might someday help people suffering from a lack of emotional connection.

Molecular and neural basis of pleasant touch sensation Science, April 29, 2022

Tom Insel

Eating Disorder Symptoms More Common Among LGBT Adults

Gay men, lesbians, bisexuals and other non-heterosexual adults are especially prone to eating disorders such as bulimia and anorexia. Previous studies suggest that such disorders may be about two to four times more common in these adults, but those estimates may be misleading. Eating disorders are notoriously underrecognized and undiagnosed because of factors ranging from social stigma to lack of awareness among clinicians. Instead of looking at rates of diagnosed eating disorders, researchers could potentially learn more about the incidence of eating disorders in gays, lesbians or any other group by examining self-reported symptoms.

Following this reasoning, Benjamin Shepherd of Nova Southeastern University and colleagues analyzed interview data from about 36,000 adults who responded to The National Epidemiologic Survey on Alcohol and Related Conditions-III in 2012-2013. About 70% identified as white. In terms of sexual orientation, 3.2% identified as lesbian or gay, 1.6% as bisexual, and 0.5% as unsure of their sexual orientation. The survey, which was designed to be representative of the entire US adult population, included questions about lowest adult weight, specific eating habits, and perceptions about weight and physical appearance.

Non-heterosexual women were more than twice as likely as heterosexual women to ever have a binge-eating episode. They were also about 60% more likely to have had binge-eating episodes over the last three months.

Non-heterosexual men were nearly twice as likely as heterosexual men to report being underweight as defined by the CDC guidelines. In addition, men who identified as gay, bisexual, or unsure of their sexual orientation were more than four times more likely to fear gaining weight and more than three times more likely to feel a loss of control when they overate compared with heterosexual men. It’s important to note that these symptoms don’t correspond directly to diagnosable eating disorders, but they do hint at risky eating patterns and potentially harmful body-related thoughts.

The general risks of eating disorders among women are already well known. These data add to our growing appreciation of the unique aspects of eating disorders in gay and bisexual men. As the study authors write, clinicians should know that non-heterosexual men may fear gaining weight and may be prone to lose control when overeating, adding that this combination of symptoms “could result in a vicious cycle and present as a barrier during treatment.”

A critical examination of disparities in eating disorder symptoms by sexual orientation among US adults in the NESARC-III International Journal of Eating Disorders, April 25, 2022.

– Matthew Hirschtritt

If you or anyone you know is considering suicide, call the National Suicide Prevention Lifeline at 1-800-273-8255. And if you’re a veteran, press 1.

Tom Insel, MD, is a psychiatrist, neuroscientist, and former director of the National Institute of Mental Health (NIMH). He is a donor to MindSite News and chair of its Editorial Advisory Board. Dr. Insel’s financial conflict of interest statement, which includes equity and advisory roles in several early-stage mental health technology companies, can be found here.

Matthew Hirschtritt, MD, MPH, is a clinical psychiatrist with the Permanente Medical Group, Inc., a mental health services researcher with the Division of Research, Kaiser Permanente Northern California, and assistant program director of the Kaiser Permanente Oakland Adult Psychiatry Training Program. His current research focuses on identification and treatment of patients with first-episode psychosis, as well as implementation of a telehealth-based mental health evaluation and referral program.

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