Poor health increasing social isolation isn't even a hard casual path to argue. Common health problems can physically restrict how often and how long one leaves the house: people on oxygen can only travel as far as their supply and weakened lungs can take them, or people with bowel disorders might be reluctant to be do anything without easy and discrete bathroom use, people with visible symptoms might be embarrassed and avoid socializing.
The loneliness-associated protein study linked in TFA doesn't seem to control for health status. So preexisting conditions may have affected the correlations.
Yes, this seems blindingly obvious to me. Maybe because I have chronic health problems myself. Perhaps those blessed with good health are blissfully ignorant.
When you are chronically ill, socializing falls pretty rapidly down your list of priorities.
That said, it seems pretty clear that incentivizing healthy socialization can significantly improve quality of life, reducing perceived suffering and quite possibly improving outcomes through reinforcement of the various social needs we have.
We are fundamentally social primates; there are prior studies demonstrating the overt harms of isolation and ostracization in humans, primates, and other mammals. Our immune systems, metabolism, and cardiovascular health are all tied intimately to things like stress and hormones, with feedback effects that can amplify disorder, or suppress it, depending on the directionality of the inputs.
I see the "just so" element of explanation to this study, but I think that even if the underlying causal factors are more complex, it is so directionally correct that I have no problem with the conclusion of the study, even if it's not correctly justified scientifically.
The loneliness-associated protein study linked in TFA doesn't seem to control for health status. So preexisting conditions may have affected the correlations.