Low heart rate variability may contribute to the risk of post-traumatic stress disorder in military personnel returning from combat deployment, suggests a new study published in JAMA Psychiatry.

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PTSD is particularly associated with service personnel deployed to war – 19% of American veterans who served in Vietnam have experienced this mental health condition.

The researchers – from the University of California, San Diego (UCSD) School of Medicine and Veterans Affairs San Diego Healthcare System – say that while previous studies have linked low heart rate variability to post-traumatic stress disorder (PTSD), it is not clear what the direction of influence might be.

Heart rate variability is the changing time interval between heartbeats. It is a sensitive measure of the health of the autonomic nervous system – the part of the nervous system that controls processes not consciously directed, such as breathing, heartbeat and digestion.

Even when we are at rest, our heart rhythm fluctuates, indicating the various changes going on in the body. Generally, high heart rate variability means things are going well.

Low heart rate variability, on the other hand, indicates a health problem. Potential problems range from asthma, depression, and heart disease to fetal distress and diabetic neuropathy.

Studies have also linked low heart rate variability to PTSD, a mental health condition that can occur after life-threatening events such as natural disasters, terrorist attacks, serious accidents and military combat.

Symptoms of PTSD include recurring memories or nightmares of the traumatic event, anger, insomnia, loss of interest, chronic depression, feeling numb, irritability and substance abuse.

PTSD is particularly associated with service personnel deployed to war. For example, 19% of US veterans who served in Vietnam have experienced PTSD at some point in their lives. Among veterans of Iraq and Afghanistan, this figure is 13-15%. These rates are significantly higher than the 8% of the general US population.

For their study, the researchers followed two large groups of active duty US marines from July 2008 to October 2013. They assessed them 1-2 months before combat deployment, and then again 4-6 months after returning home.

The results showed that the marines who had reduced heart rate variability before deployment were more likely to develop PTSD when they returned, even after taking into account deployment-related combat exposure.

First author Arpi Minassian, clinical professor of psychiatry at UCSD, says the evidence is “initial and modest,” and:

It suggests that an altered state of the autonomic nervous system may contribute to vulnerability and resilience to PTSD, along with known risk factors, such as combat exposure and preexisting stress and trauma symptoms.”

The researchers say that if these initial findings are confirmed in further studies, they may lead to opportunities to prevent PTSD by targeting the autonomic nervous system.

Meanwhile, Medical News Today recently learned that work stress may be as bad as secondhand smoke when it comes to damaging our health. The Harvard and Stanford study suggests that workers with high job demands are 50% more likely to be diagnosed with a medical condition.