A new study by researchers at Lund University, Sweden shows that women can have a considerably higher risk than men of developing chronic obstructive pulmonary disease (COPD). Using a new diagnostic method, researchers have now shown that the risk of developing COPD can be twice as high for women as it is for men. This means that female sex may be an independent risk factor for developing COPD.
Johannes Luoto, a researcher at Lund University and a doctor at the geriatric clinic of Skåne University Hospital, has followed an initial group of 2,300 people aged between 65 and 100 to study the development of this disease. “We see a clear increased risk for women contracting COPD compared with the risk for men. And it applies even when other risk factors, such as smoking and age, are taken into consideration”, says Luoto.
It was not certain previously whether there was a gender difference for the risk of developing COPD, and that is partly due to the fact that there are few studies that examine who is at risk for the disease. Another factor is that there has been a recent change in the way that COPD is diagnosed, comments Luoto: “The few studies that have been done use methods to interpret pulmonary function involving spirometry test criteria which the European and American lung research organisations ERS and ATS now consider outdated and unable to produce reliable results. These older methods do not consider the age or sex of the examined subject when interpreting the lung-function even though we know that normal aging effects lung-function and suspect that there may be differences between sexes”
“Our study is one of the first that uses more advanced diagnostic criteria, which take into consideration factors such as gender and age before interpretation of the spirometry results and deciding whether you have COPD or not”, states Luoto.
This is a new way of interpreting the pulmonary function examination, which makes considerable differences to the results: besides the effects of advanced age and smoking, researchers using the more modern method LNN, Lower Limit of Normal, in their study have seen clear differences between the genders for the risk of developing COPD; and there was previous evidence that women’s airways could be more sensitive than men’s, but the older diagnostic methods have not shown with any certainty that there is a difference between the genders regarding the risk for contracting COPD.
“Researchers and the doctors involved have not yet agreed on the method that is to be used in practice. Further studies are needed to compare the methods”, says Luoto.
The previously known main risk factors for developing COPD are smoking and air pollution. The disease, which has no cure, is one of the world’s most common causes of death according to the World Health Organisation.
The true incidence of chronic obstructive pulmonary disease is largely unknown, because the few longitudinal studies performed have used diagnostic criteria no longer recommended by either the European Respiratory Society or the American Thoracic Society (ATS).
We studied the incidence and significance of airflow limitation in a population-based geriatric sample using both an age-dependent predicted lower limit of normal (LLN) value and a fixed-ratio spirometric criterion.
Out of 2025 subjects with acceptable spirometry at baseline, 984 subjects aged 65–100 years completed a 6-year follow-up visit. Smoking habits were registered at baseline. Exclusion criteria were non-acceptable spirometry performance according to ATS criteria and inability to communicate. Airflow limitation was defined both according to forced expiratory volume in 1 s (FEV1)/forced vital capacity ratio The incidence of airflow limitation per 1000 person-years was 28.2 using a fixed ratio and 11.7 with LLN, corresponding to a 1.41-fold higher incidence rate using a fixed ratio. The incidence increased dramatically with age when using a fixed ratio, but less so when using LLN. In addition, a sex effect was observed with the LLN criterion. LLN airflow limitation was associated with increased 5-year mortality. Presence of fixed-ratio airflow limitation in individuals classified by LLN as non-obstructive was not associated with increased mortality.