孤独不利健康——绝对和肥胖一样糟糕，可能也和吸烟一样有害。因此，在疫情肆虐的日子里，在许多地方，人们被迫独处，如何阻止独处转化为孤独是一个紧迫的医学问题。

 

Loneliness is bad for your health—certainly as bad as being obese¹, and possibly as bad as being a moderate smoker².So, in these days of plague, when enforced solitude³ is the order of the day in many places, how to stop solitude turning into loneliness is a pressing medical question. One part of the answer is to try to understand the physiology⁴ of the change. And that has, for the past few years, been the objective of Steven Cole of the University of California, Los Angeles.

 

Dr Cole began his work with a study he published in 2015, in collaboration⁵ with John Cacioppo of the University of Chicago.

 

The pair led a team of psychologists, neuroscientists and immunologists who found that the pattern in people's blood of immune cells called myeloid cells is notably⁶ different in those who score as "very lonely" on loneliness tests compared with those who do not.

 

Lonely people have unusually low numbers of a type of myeloid cell that generates what are known as interferon responses, which hamper⁷ viral replication.

 

This makes them particularly vulnerable to viral infections. They also have an abundance of a second type of myeloid cell,one that promotes the activity of genes⁸ which drive inflammation— and it has been known for years that those who feel lonely experience more inflammation than those who do not.

 

These correlations⁹ are intriguing¹⁰, but do not explain which comes first, the loneliness or the myeloid response.

 

Dr Cole and Dr Cacioppo addressed that question by repeatedly measuring perceptions of social isolation¹¹ in individual volunteers,while simultaneously¹² tracking, from blood samples, their gene-expression patterns and other changes in their physiology.

 

They found that, initially¹³, volunteers' feelings of isolation coincided with an increase in their inflammation genes' activity and a concomitant increase in the circulation of immature¹⁴ immune cells, called monocytes, that are involved in inflammation— and which are also known to travel into the brain and promote anxiety.

 

They noted¹⁵, too, increased levels in the brain of signalling molecules¹⁶ associated with both inflammation and behaviours such as social withdrawal¹⁷, feelings of suspicion towards the outside world and a tendency to act more defensively by making decisions that involve few risks.

 

That, of course, promotes further feelings of loneliness. Which, in turn, trigger a further myeloid response. And so on.

 

It seems, therefore, that though loneliness starts with solitude, it can quickly take on a physiological¹⁸ life of its own.

 

Dr Cole thus worries that the enforced isolation, brought about by current circumstances, of those who are already living alone may create in many people a state of chronic¹⁹ loneliness that is difficult to escape from when things start returning to normal.

 

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