Loneliness is associated with weaker immune systems, greater sensitivity to physical pain, and other health measures that imply that, at some point, even our own bodies don't like us.

PROBLEM: "Because the need for social connection is central to human nature, the failure to fulfill this need should be detrimental to mental and physical health," write researchers at Ohio State (emphasis mine). The thing is, even though we know that loneliness sucks, we don't completely understand the implications of a life spent significantly cut off from the company of others.

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METHODOLOGY: In two related studies, the researchers gathered first overweight but otherwise healthy middle-aged adults, and then breast cancer survivors. They took blood samples and subjected the participants to stress tests, among other ordeals. They evaluated their social lives by means of the UCLA Loneliness Scale, which deals with perceptions of loneliness which, when it comes down to it, matter more than how many people they may actually be surrounded by or the number of Facebook friends they tally.

RESULTS: The loneliest of the otherwise healthy participants had more markers of inflammation when tasked with a stressful activity, like speaking in front of others or doing math.

The lonelier breast cancer survivors, in addition to increased inflammation, experienced more pain, depression, and fatigue. Reactivation of latent herpes viruses, which tends to be triggered by stress, can also be used a measure of immune response. Here, those who scored higher for loneliness showed more signs of herpes reactivation.

CONCLUSION: Loneliness acts as a stressor, is associated with a variety of "dysfunctional immune responses," and may well be harmful to our health.

IMPLICATIONS: It can be stressful to be alone, with detrimental effects just as any type of stress warrants. Loneliness as a chronic stressor, as these results indicate it may be, can therefore be tied to everything from heart disease to Alzheimer's.

Of course, "It's also important to remember the flip side, which is that people who feel very socially connected are experiencing more positive outcomes," said lead author Lisa Jaremka. But if you're already lonely, don't let that make you feel worse.

The research was presented at the Annual Meeting of the Society for Personality and Social Psychology.