Wealthier children and young adults may be more likely to die from asthma than their poorer peers, according to a new study.
For many conditions, being poor has been linked to worse health outcomes.
A new study, published in the journal Thorax, found that asthma mortality among children and younger adults in England was more common in more affluent areas.
Experts from St George's, University of London, and the University of Edinburgh used national datasets to compare asthma outcomes across England over a number of years.
In England, there were 14,830 recorded asthma deaths between 2002 and 2015, including more than 1,400 among children and adults aged five to 44.
There were more than half a million emergency asthma admissions from 2001 to 2011 among patients aged five and over.
After analysing the data, the researchers said they found an "unusual and unexpected pattern" where asthma mortality among those aged five to 44 was more common in richer areas.
In most age groups the rate of asthma deaths was generally higher as deprivation increased, apart from those aged five to 44, where researchers noted a "modest but significant decrease in deaths from asthma with increasing levels of relative deprivation".
Among five to 44-year-olds, mortality was 19% lower among the most deprived 20%, compared to the wealthiest 20%.
The authors said this was an "unexpected phenomenon" and called for further research to investigate the finding.
They speculated that it may be that affluent areas may have a higher prevalence of "a less predictable, more 'brittle'" form of asthma which can progress more rapidly and lead to death.
There may also be higher prevalence of allergies in richer groups.
Despite improvements in care and falling numbers of asthma deaths, the UK still has among the highest global mortality rates in the young, the researchers said.
It also has significant differences in asthma outcomes per different region and socio-economic background, they added.
For instance, asthma sufferers in the West Midlands are more likely to die than patients in other parts of the country.
Researchers found that mortality rates in the region were about a third higher than the England average.
Meanwhile, emergency admissions for the condition - which affects more than five million people across the UK - were most common in the North West.
Dr Samantha Walker, director of research and policy at Asthma UK, said: "It is concerning and unexpected that younger people in England who are wealthy have a higher risk of dying from the condition than those who are poor.
"More research needs to be done to fully understand the relationship between someone's socio-economic status and how their asthma might affect them.
"We are also urging people with asthma to make sure they have a written asthma action plan, take their preventer medicines regularly and get the support they need to manage their condition from Asthma UK at www.asthma.org.uk/manage."
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