The Effect of Long Term Inhaled Corticosteroids on the Risk of Cardiovascular Morbidities

Globally, cardiovascular disease is a major cause of mortality and morbidity. In the past 2 decades in Hong Kong, it has been the second leading cause of death, with death rate reaching 50/100,000 population in 2006, and the third leading cause of hospitalizations in Hospital Authority Hospitals between 2001-2005. The disease burden is huge and effective control measures should target at prevention level. There has been substantial evidence from landmark epidemiological studies in the past 10 years that chronic low grade systemic inflammation, predominantly based on plasma hs-CRP, is an independent predictor for the development of hypertension, myocardial infarction, stroke, cardiovascular death and peripheral vascular disease. A dose-dependent risk association between hs-CRP and these cardiovascular morbidities has also been consistently demonstrated. Asthma is a chronic inflammatory airway disorder associated with airflow obstruction and bronchial hyper-responsiveness, which affects about 10% of population in Hong Kong. It is a major respiratory disease in Hong Kong that carries significant morbidity and high hospitalization burden in all ages. The use of long-term inhaled corticosteroid (ICS) treatment in recent decades has become the cornerstone in the treatment of most patients with persistent asthma with reduction in its mortality and hospital utilization. The ultimate goal of treatment is to achieve optimal control of airway inflammation and to reduce mortality and morbidity. Although the pathogenesis of asthma is incompletely understood, studies have shown that it is associated airway inflammation and a state of increased free radical formation, because cells derived from airways and peripheral blood of patients with asthma generate increased amount of reactive oxygen species, the level of which is related to severity of asthma. Recent preliminary studies have indicated that, apart from the presence of chronic airway inflammation, asthma may also be associated with chronic low grade systemic inflammation and increased oxidative stress. Intuitively, this asthma-related systemic inflammation may increase the risk for development of cardiovascular and cerebrovascular diseases. Despite the propensity of asthma towards cardiovascular morbidity, recently, several epidemiological studies utilizing large numbers of patients with asthma have shown that long term use of ICS is independently associated with a protective effect towards the development of myocardial infarction and cardiovascular mortality, with protective risk at 0.35 (95%CI 0.13-0.93). This effect is possibly mediated through the reduction of low grade systemic inflammation as reflected by plasma hs-CRP from systemic absorption of the ICS. This potential effect of ICS on reduction of chronic low grade systemic inflammation has an invaluable implication for its future application as a preventive medicine against the development of cardiovascular morbidities and mortality, especially in high risk patients. ICS have been launched for more than 20 years, and is currently the first-line treatment for asthma. Their systemic side effects are much less than that of oral corticosteroids. Long term safety of ICS in adults is generally very high, but mild increases in risk of osteoporosis, cataracts and glaucoma have been reported in patients with high dose ICS use. The purpose of this study is to explore the potential protective effect of ICS on cardiovascular morbidities and its underlying link with systemic inflammation in Chinese adults with asthma compared with matched controls from the general population.