Women may be twice as likely to have asthma as men because testosterone protects against it, scientists have found.
Almost one in 10 British women suffer from asthma, which, like arthritis and multiple sclerosis, is more common in females than males.
Now it has emerged women have more of a type of immune cell linked to asthma.
These cells produce proteins which increase mucus and inflammation in the lungs and can lead to wheezing and breathlessness.
But testosterone was found by US researchers to block them and slash the number of these damaging proteins.
Asthma risk: A new study reveals women have a higher risk since testosterone protects against it
HAVING A CHEST INFECTION AS A CHILD RAISES AN ADULT’S RISK OF ASTHMA BY UP TO FOUR TIMES
Having a chest infection as a child raises a person’s risk of asthma by up to four times, research revealed in September.
Suffering from a lower-respiratory tract infection, such as bronchitis or pneumonia, before the age of five increases an individual’s likelihood of developing the lung condition by between two and four times, a study found.
An upper-respiratory tract infection, including a cold or tonsillitis, raises the risk by 1.5 times.
Study author Dr Evelien van Meel from the Erasmus Medical Center in the Netherlands, said: ‘These findings support the hypothesis that early-life respiratory tract infections may influence the development of respiratory illnesses in the longer term.
‘In particular, lower-respiratory tract infections in early life seem to have the greatest adverse effect on lung function and the risk of asthma.’
‘Our findings may help develop a treatment for asthma’
Senior author Dr Dawn Newcomb, from the University of Vanderbilt, said: ‘Our findings may help develop a treatment for women’s asthma.
‘Testosterone probably has too many other effects to be used as a drug, but treatments are already in trials which may be more beneficial for women with asthma compared to men with asthma.’
Dr Samantha Walker, director of research and policy at Asthma UK, said: ‘While we have known for some time that women are more likely to have asthma than men, this study is promising because it gives us a deeper understanding of the part that hormones play in the condition.
‘We have known for a long time that there is a link between hormones and asthma, but this new study goes one step further in identifying a cell which is more prevalent in women with asthma.
‘It also suggests that some hormones can suppress these cells and, in the future, they could be used to help people with asthma.’
Female sex hormones do not protect against asthma
The study, led by Vanderbilt University Medical Centre in Tennessee, helps to explain why young boys are more likely to have asthma than girls only up until their teenage years.
The testosterone flooding male bodies when puberty hits is thought to protect them, so that men are then less likely to have asthma than women.
Around 5.4 million people in Britain have asthma, which often starts in childhood but can also appear for the first time in adults.
The main symptoms of the common lung condition are coughing, breathlessness, a tight chest and wheezing, and asthma attacks kill three people a day in the UK.
The US researchers collected blood samples from 21 people of both sexes with and without asthma to discover that women had more lung cells called ICL2 cells.
These cells are responsible for the overreaction of the immune system which causes asthma by producing proteins called cytokines which make it harder for people to breathe.
Mice also have these cells and when researchers fed the animals pellets containing testosterone, they found their ICL2 cells produced fewer proteins.
The study, published in the journal Cell Reports, also used female sex hormones like oestrogen and progesterone on the mouse cells.
However these had no protective effect, suggesting women’s sex hormones are of no help in fighting off asthma.
Dr Newcomb said: ‘When we started this study, we really thought that ovarian hormones would increase inflammation, more so than testosterone making it better.
‘I was surprised to see that testosterone was more important in reducing inflammation.’
But she added: ‘Sex hormones are not the only mechanism but, rather, one of many mechanisms that could be regulating airway inflammation.’