Loneliness can be a drag. When you want solitude you can't always get it, but sometimes when all you yearn for is companionship, it can feel like nothing you can do to make that a reality. It's enough to make you feel sick.

No, seriously, it can literally make you sick and mutate your genes.

Doctors have long known that loneliness can be linked to everything from heart disease to Alzheimer's and that it can speed the spread of cancer. A new study published this week in the Proceedings of the National Academy of Sciences looks at why the immune systems of lonely people appear to work differently.

The study's authors claim that loneliness is "linked to increased risk of chronic diseases and mortality," not to mention an increase in inflammation caused by overactive white blood cells and a lower level of the antiviral compounds that help ward off infection. Because the human body isn't capable of taking on high levels of inflammation caused by years of loneliness, "that explains very clearly why lonely people fall at increased risk for cancer, neurodegenerative disease and viral infections as well," the lead author of the study, genomics researcher Steve Cole said in an interview with NPR News.

In order to figure out how loneliness could possibly change our body's makeup, Cole and his team tracked 141 people for five years, asking the participants to rate their loneliness every year and taking blood samples to "track the activity of genes involved with immunity and inflammation." The researchers also kept an eye on the hormone norepinephrine, one of the two signals activated during our primal flight-or-fight response.

One of the things Cole noted was that when people were feeling lonely, they had much higher levels of norepinephrine in their blood, which might explain the changes in the immune systems of people who are feeling isolated. "It's this surge in these pro-inflammatory white blood cells that are highly adapted to defend against wounds," he said, explaining that when someone's life is threatened, norepinephrine pours into the body and begins shutting down immune functions while pumping up the production of white blood cells. "But at the expense of our defenses against viral diseases that come from close social contact with other people."

To make matters worse, Cole found that as all that is happening, the bodies of lonely people also seem to block the genes that would allow their bodies to absorb cortisol, which helps to lower inflammation. Though it sounds like all bad news, Cole said that if loneliness was truly life-threatening, the body would switch into the same defensive mode it does when it feels like it is actually in imminent danger.

"At this point, my best guess was that loneliness really is one of the most threatening experiences we can have," he said. "Though I didn't think of loneliness as being that awful. It's not pleasant, but not something my body should be getting all up in arms about."