Women with asthma were found to have significantly higher blood serum levels of leptin than those without asthma.
The study included 5,876 adults who took part in a health and nutrition survey between 1988 and 1994. The participants completed a questionnaire about age, sex, BMI and asthma diagnosis, and provided a blood specimen for analysis.
Based on this data, 290 participants were classified as having current asthma, and 5,586 as never having had asthma. Their blood samples were analysed to determine their early morning serum leptin concentrations.
The researchers found that both a high BMI and a high serum leptin level were associated with an increased risk of asthma. After adjusting for other risk factors, a high leptin level was found to be associated with a 56 per cent increased risk of having current asthma.
The researchers found that high BMI was significantly associated with asthma in women, but not men.
High leptin levels were also associated with a higher asthma risk in women than men, with the strongest association in pre-menopausal women.
Women in the top quartile of leptin concentrations had an 85 per cent increased asthma risk compared with a 27 per cent increased risk in men in the top quartile.
The researchers had thought that the link between high leptin levels and asthma risk could account for the association between BMI and asthma previously documented. This was not supported by their findings.
Lead researcher Dr Akshay Sood, from the division of pulmonary and critical care medicine at Southern Illinois Uni- versity School of Medicine said: 'We tried to find whether the effects of leptin would explain the association between obesity and asthma which have been previously established.
'We did find an association between leptin and asthma but also found the association between obesity and asthma could not be explained by leptin alone,'