Overweight 'higher asthma risk'

People who are overweight have a 50% higher risk of developing asthma, scientists have said. US researchers reviewed seven studies involving over 330,000 adult patients, the American Journal of Respiratory and Critical Care Medicine reported.

They said obesity was well-established as a risk factor for diabetes and heart disease, and that asthma could now been added to that list. UK experts agreed there was a link, but said the reasons were still unclear.

Asthma affects the small tubes - airways - that carry air in and out of the lungs. When something triggers asthma, the muscle around the walls of the airways tightens so that the airway becomes narrower. The lining of the airways becomes inflamed and starts to swell and mucus or phlegm can be produced. These reactions cause the airways to become narrower and irritated, which leads to the symptoms of asthma - such as wheezing, shortness of breath and a tight chest.

More than 5m people in the UK are currently being treated for asthma.

The study, by a joint team from the US National Jewish Medical and Research Center and University of Colorado, classed normal weight as someone with a body mass index below 25, overweight over 25 but below 30, and obese as 30 and above. The analysis showed that for every normal weight person with asthma, there were 1.5 people with asthma who were overweight or obese. The risk of having asthma for those who were obese was twice that of someone with normal weight. Researchers could not pinpoint what caused the increased risk of asthma.

Obesity causes impairments in lung function, such as a reduction in lung volume and an increase in the amount of oxygen used during breathing, but these on its own would not be enough to induce the condition. And the researchers warned the symptoms associated with this, such as breathlessness, could have been wrongly interpreted as asthma.

But lead researcher Dr Rand Sutherland still said the link was valid. "If significant weight loss could be achieved in the population of overweight and obese individuals, it could be estimated that the number of new asthma cases could fall significantly. Obesity is a well-established risk factor for diabetes, stroke, cardiovascular disease and arthritis. The findings support the addition of asthma to that list."

A spokeswoman for Asthma UK said: "There is long-standing evidence that obesity and asthma are linked. This new research attempts to clarify this relationship, however the exact reasons remain unclear. Other studies have shown that losing weight and getting fitter can help in both managing asthma and improving lung function, which supports our advice to people with asthma that a healthy, balanced diet and regular exercise can help them to feel more in control of their condition."