My reaction to this is the same as when I first listened to Sam Harris’ conversation with Robert Waldinger (interviewee in the article): I am in danger.
No your not. There is no proof that this is true. Have they even confirmed the stress hormones? "what we think happens is that the body stays in a kind of low-level fight-or-flight mode, and that means that there are higher levels of circulating stress hormones and higher levels of inflammation" shows tells me they have not but this would be an easy thing to measure. I argue that having friends can cause more stressful having to listen to all their aches and pains, pick them up, etc. The reason for the higher mortality rate may be when accidents happen, nobody is there to call 911 and you're dead or perhaps you take on all work by yourself(roofing, concrete, etc). I'm in the same boat but I am too busy to worry about loneliness.