Life at the bottom of the social ladder can be damaging to health - even for monkeys, research has shown.
A study of rhesus monkeys has revealed the stress of low social status can be damaging to the immune system of the animals.
Researchers believe the findings may help explain why people with poor and deprived backgrounds have higher rates of heart disease and diabetes, both of which are linked to inflammation.
Dr Noah Snyder-Mackler, of Duke University in the US, who co-led the investigation, said: "Social adversity gets under the skin. If we can help people improve their social standing and reduce some of these hierarchies, we may be able to improve people's health and wellbeing."
In the US, life expectancy between rich and poor differs by more than a decade.
American health inequality is often attributed to the availability of medical care and lifestyle habits such as smoking, exercise and diet.
But the new results, published in the journal Science, underline the important role played by stress.
The team studied female rhesus monkeys at the Yerkes National Primate Research Centre at Emory University.
First, 45 unrelated females that had never met were sorted into social groups and observed as they formed a social pecking order. Monkeys introduced to their groups earlier tended to be ranked higher than the "last in".
To find out how rank affected health, scientists measured the activity of 9,000 genes in the animals' immune cells.
Activity in more than 1,600 genes differed between lower and higher-ranking monkeys, which was especially true within "natural killer cells" - white blood cells that are a first line of defence against infection. The cells were more active in higher-ranking monkeys, giving them better protection against viruses.
Lower-rankers produced a stronger immune response against bacteria, but this also fuelled potentially harmful inflammation. When their immune cells were exposed to a bacterial toxin in test tubes, they went into overdrive.
Co-author Dr Luis Barreiro, of the University of Montreal in Canada, said: "A strong inflammatory response can be life-saving in the face of infectious agents. But the same self-defence mechanism, the ones that make infected tissue swollen and red, can also cause damage if not properly controlled."
When the monkeys were re-sorted so that low-rank animals were moved up the social ladder, it had a striking effect on their immune systems.
As the animals improved their social status and enjoyed the benefits, such as more grooming, their immune cells became less likely to trigger inflammation.
"This suggests the health effects of status aren't permanent, at least in adulthood," said Dr Jenny Tung, another member of the Duke team.
Why are you making commenting on The Herald only available to subscribers?
It should have been a safe space for informed debate, somewhere for readers to discuss issues around the biggest stories of the day, but all too often the below the line comments on most websites have become bogged down by off-topic discussions and abuse.
heraldscotland.com is tackling this problem by allowing only subscribers to comment.
We are doing this to improve the experience for our loyal readers and we believe it will reduce the ability of trolls and troublemakers, who occasionally find their way onto our site, to abuse our journalists and readers. We also hope it will help the comments section fulfil its promise as a part of Scotland's conversation with itself.
We are lucky at The Herald. We are read by an informed, educated readership who can add their knowledge and insights to our stories.
That is invaluable.
We are making the subscriber-only change to support our valued readers, who tell us they don't want the site cluttered up with irrelevant comments, untruths and abuse.
In the past, the journalist’s job was to collect and distribute information to the audience. Technology means that readers can shape a discussion. We look forward to hearing from you on heraldscotland.com
Comments & Moderation
Readers’ comments: You are personally liable for the content of any comments you upload to this website, so please act responsibly. We do not pre-moderate or monitor readers’ comments appearing on our websites, but we do post-moderate in response to complaints we receive or otherwise when a potential problem comes to our attention. You can make a complaint by using the ‘report this post’ link . We may then apply our discretion under the user terms to amend or delete comments.
Post moderation is undertaken full-time 9am-6pm on weekdays, and on a part-time basis outwith those hours.
Read the rules here