Researchers find proteins linked to heart disease increase when dwelling on negative thoughts.

The connection between the body and mind is strong and conditions like depression can wreak havoc on our health.

Depression shortens a person’s lifespan, on average by 14 to 32 years but not just because of suicide, according to the National Institute of Mental Health.

People with serious mental illness are more likely to suffer from chronic diseases related to addiction, obesity, and poverty.

Besides these factors, emerging research is shedding light on how physical and mental health are intertwined, particularly how depression can affect a person’s cardiovascular health.

Much of it relates to proteins such as interleukin-18 (IL-18) and factors that increase its prevalence in the body.

Researchers have found higher IL-18 concentrations in people who smoke, those with lower high-density lipoproteins — also known as “good” cholesterol — levels, and high triglycerides.

A 2011 study of 5,661 middle-aged men found that increased levels of interleukin-18 in the blood “is prospectively and independently” associated with an increased risk of cardiovascular disease. The researchers noted, however, the association was modest in strength.

But new research suggests that sadness can raise those levels as well.

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Researchers at the University of Texas Health Science Center at Houston have found another way mood can affect a person’s physical health.

Using positron emission tomography (PET) scans and blood tests, the research team examined the differences in the brains of 28 women, 13 of whom had unmedicated depression. Those with depression had higher levels of IL-18 and showed higher levels of opioids, neurotransmitters that act to reduce the impact of stress on the body.

The women were first asked to think of something neutral. As they did, levels of IL-18 and opioids decreased.

Next, they were instructed to focus on a sad event in their lives. Both groups of women experienced increased opioids and IL-18.

“These effects were observed during sadness in both groups, but were much greater in people with major depression as compared to non-depressed, otherwise healthy people,” lead researcher Alan Prossin, assistant professor in the Department of Psychiatry and Behavioral Sciences at John P. and Kathrine G. McGovern Medical School, said in a press release.

Interestingly, the level of IL-18 in depressed women increased after thinking about the sad event but not to the levels they had been before the experiment began. According to researchers, this suggests the neutral thoughts lowered IL-18 and that effect lingered even after they were asked to think of sad things.

“Sad mood induction results in a substantial increase in plasma IL-18 concentration, potentially in response to heightened levels of perceived emotional stress consequent to recollection of the prior sad event,” the researchers wrote in their study, which appeared in the latest issue of the journal Molecular Psychology.

The researchers said therapies that improved mood could lower IL-18 levels, thus lowering a person’s risk for chronic illness. They did, however, note more studies with more research subjects are needed to confirm their findings.

These increased risks underscore the importance of getting help for depression.

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While researchers continue to delve into how our mental health influence our physical health, others are discovering the opposite appears to be true as well.

A study published in JAMA Psychiatry found people with increased inflammation from either immune disorders or infection had increased risks of mood disorders.

That study, which involved 3.5 million people from Denmark, found patients with an autoimmune disease were 45 percent more likely to have a mood disorder while any history of infection increased the risk of a mood disorder by 62 percent.

“The associations found in this study suggest that autoimmune diseases and infections are important … factors in the development of mood disorders in subgroups of the patients possibly because of the effects of inflammatory activity,” the researchers wrote.

Other research over the past decade has found people with increased levels of proteins and other byproducts of inflammation are associated with psychological distress, depression, and suicidal tendencies.

Researchers at the Department of Psychiatry and Behavioral Sciences at the Emory University School of Medicine concluded that the body’s inflammatory response have an important role in the development of depression. They found depressed patients have higher levels of proinflammatory cytokines, which promotes inflammation throughout the body.

One of their studies, published in 2006, suggests depression could be a behavioral byproduct of adapting genes that promote inflammation, but targeting certain proinflammatory cytokines could be a new and novel way to treat depression.

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