Scientists in Britain say they have discovered a link between obesity and asthma and they believe the connection may explain why overweight people are up to twice as likely to develop the respiratory condition.
The scientists at the Centre in Allergic Mechanisms of Asthma at King's College London suggest there is a common underlying process behind many cases of combined obesity and asthma as the sharp increase in obesity in recent decades have also been seen in asthma.
This study is however the first to uncover evidence that the two could be linked and the researchers believe it could lead to new drugs to treat both conditions.
With asthma the immune system overreacts and cells which normally fight off parasites, respond instead to grass pollen, house dust mites and pet allergens; in the lungs, these cells which are called known as Th2 cells, cause inflammation which triggers asthma.
The British researchers extracted Th2 immune cells from the blood of obese asthmatics and found that as well as causing asthma, they secreted high levels of a hormone, promelanin which is usually found in the brain.
Promelanin plays a crucial role in controlling appetite and the researchers say the discovery may explain why obesity and asthma often go together.
Dr. David Cousins, an immunologist at the centre, says it is already known that women who are obese are twice as likely to be diagnosed with asthma and when obese people with asthma manage to lose weight, their asthma usually improves.
It had previously been suspected that the two conditions were linked simply because people with asthma put on weight because of difficulties in exercising.
Professor Tak Lee, director of the Centre says the finding implies that both asthma and obesity which are both serious health problems, could be tackled together.
The scientists say the discovery does not account for all cases of asthma and obesity but possibly leads in some people to a vicious circle whereby an obese person develops asthma, and then becomes more obese because their immune cells churn out more promelanin.
Professor Lee says it clearly is not the only issue in obesity and they are interested in exploring whether there is a genetic factor involved as there are many fat people without asthma and many asthmatics who aren't fat.
Other teams too are exploring whether promelanin can be targeted to suppress appetite but it is unclear whether when the protein is suppressed other important effects occur.
Since the eighties obesity rates in England have risen dramatically, from 6% in men and 8% in women to 23% in both sexes in 2004.
Asthma now affects 5.2 million people in the UK, 2.6 million of those severely and childhood asthma rates have more than doubled since the sixties.
Asthma currently affects 15.7 million in the U.S. and costs health services billions each year.
According to the Royal College of Physicians there are only 29 fully-trained allergy consultants in the country and experts say there is also a serious lack of knowledge at the local doctor level.
Health experts suggest the rise in asthma may be put down to exposure to air pollutants, overuse of antibiotics and reduced intake of fruit and vegetables.
The study appears in the journal Proceedings of the National Academy of Sciences.