-For Steve Cole, the connection between loneliness and chronic diseases became clear when studying the HIV crisis in the 1990s.

-One of the things we figured out early in the context of HIV infection is that your social life mattered.

For instance, gay men who were in the closet got sick and died 30% faster than the guys who were out of the closet.

So there's something about how you live your life that was getting into the body and changing the way the virus was working.

And when we looked at the "fight or flight" biology of these folks, that's exactly what they found.

Their nervous systems were just running this constant low-grade stress factory in their body.

♪♪ -Cole's research centered on norepinephrine, a neurotransmitter that enables this "fight or flight" response.

-We could do simple little experiments where we take some HIV virus, put it on some white blood cells, some immune cells, in a test tube, and then just add some norepinephrine in there as if these cells had just been exposed to "fight or flight" stress biology.

It turns out the virus replicates somewhere between 3 and 5 times as fast in that scenario.

-Cole expanded his research to find out if the stress of loneliness and social isolation could be driving other diseases, as well.

-We went systematically through all of the genes to help us understand what was going on in lonely people getting sick with these chronic diseases.

We could localize what might be operating differently in the immune cells of a lonely person versus a non-lonely person.

-We've been able to find that genes that are activated in people who are lonely look very systematically different.

-Honestly, it was the easiest data analysis I have ever seen in my entire life because it was just so clear what had happened.

If you took all of the genes in the genome and you found the ones that were most overactive in the white blood cells of lonely people, they were all involved in inflammation.

-Different inflammatory markers are associated with different medical conditions, with cardiovascular disease, with an increased risk of dementia, with diabetes.

You name it, there is a medical condition that inflammation will affect.

That is part of the reason why loneliness is so pernicious.

-If your body was running this kind of molecular program of more inflammation and less antiviral response, yeah, you're going to get exactly the diseases that lonely people get.