Apple-shaped women's asthma risk 

　　But some researchers argue that waist circumference may be a more useful measure because it more closely reflects levels of visceral fat deposits found around the body's organs.

　　Visceral fat is metabolically different from other types of fat found in the body, and may have different - and more profound - effects on health.

　　Researcher Julie Von Behren said: "Visceral fat is metabolically more active - it can produce compounds that may cause inflammation. Inflammation may then be related to asthma."

　　Healthy lifestyle

　　Leanne Metcalf, director of research at the charity Asthma UK, said the researchers had not taken into account other factors which might have influenced the development of asthma, such as a family history of the condition.

　　However, she said: "As this study involves such a large number of women, the results are likely to have some significance.

　　"It is important that people with asthma eat a healthy, balanced diet, which is low in fat and sugar, and take regular exercise.

　　"Taking these steps can aid weight loss, improve lung function and help get asthma symptoms under control, especially given the established links between high levels of abdominal fat and other long-term health conditions."

　　Dr Noemi Eiser, of the British Lung Foundation, agreed that the study reinforced the need for women to lead a healthy lifestyle and for them to be more aware of the health risks of having a large waist size.