Overweight people are 50 percent more likely to develop asthma than those with normal weight, a new study has revealed. The latest study, which reviewed seven studies involving over 330,000 adult patients, said excess weight causes impairments in lung function, such as a reduction in lung volume and an increase in the amount of oxygen used during breathing, which could be one of the factors in triggering asthma.

Asthma is a chronic disease of the respiratory system in which the airway occasionally constricts, becomes inflamed, and is lined with excessive amounts of mucus, often in response to one or more triggers. These episodes may be triggered by such things as exposure to an environmental stimulant (or allergen), cold air, exercise or exertion, or emotional stress.

This airway narrowing causes symptoms such as wheezing, shortness of breath, chest tightness, and coughing, which respond to bronchodilators.

The American Journal of Respiratory and Critical Care Medicine reported that experts have agreed there is a link between asthma and obesity but said they are not able to determine the exact causes.

The study, which compared participants with normal Body Mass Index, said asthma was 38 percent more common in overweight adults and nearly twice as common among obese adults. People with normal weight are those who have BMI below 25, overweight over 25 but below 30, and obese as 30 and above.

BBC quotes lead researcher Dr. Rand Sutherland as saying, "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," he added.

According to the World Health Organization, asthma is responsible for around 180,000 deaths around the world annually.