Effect of Inhaled Steroids on Glucose Regulation in Asthma Patients

Inhaled corticosteroids (ICS) have been shown to have many side effects that are consistent with systemic corticosteroids, suggesting that its systemic absorption can lead to adverse effects in the long term users. ICS can pose a major health impact in the community, especially when its use has become widely accepted as mainstay treatment for asthma and chronic obstructive airway diseases in recent decades.

In 1997, inhaled corticosteroids were shown to increase the risk of nuclear cataracts by 1.5-fold and posterior subcapsular cataracts by 1.9-fold respectively. Besides, high dose ICS use for more than 3 months increased risk of open angle glaucoma with OR 1.44. In 1998, a case control study demonstrated positive association of cataract extraction in elderly ICS users. ICS use of more than 3 years increased cataract by 3-fold in high dose users (> 1mg daily budesonide dipropionate). Whereas low dose use (\<1mg daily budesonide dipropionate) for more than 2 years increased cataract by 1.6-fold. Subsequent studies also found increased risk of osteoporosis in long term ICS users.

It has been well known that systemic corticosteroid causes diabetes by inducing insulin resistance. Previous study showed a 2-fold increased risk of diabetes in patients using systemic corticosteroids.

Nevertheless, of the many systemic side effects that are known to inhaled corticosteroids, its effect on the risk of diabetes has not been established yet.

There have also been 2 small scale studies about the effect of ICS on insulin resistance profile, however, the study findings were also inconclusive.

In 1987, a study of 9 subjects, given 4 weeks of inhaled budesonide dipropionate 1mg daily, were shown to have increase in 2-hour peak glucose level in oral glucose tolerance test, and also increased fasting serum insulin concentration, suggesting that ICS use was associated with glucose dysregulation and increase insulin resistance. Subsequently, in 1993, another study of 15 subjects with unstable asthma compared to 15 normal control subjects, a reduction in insulin resistance in patients with uncontrolled asthma was noted upon 1 month of ICS treatment; while the insulin resistance profile became static at 5 and 8 months of therapy. This study suggests that insulin resistance profile is increased in subjects with unstable asthma in relation to the stress induced during exacerbation. ICS can reduce insulin resistance profile by stabilizing asthma control.

In terms of researches relating ICS to diabetes, there are limited studies in the elderly. In 1998, a study showed dose dependent worsening of diabetic control in the diabetic elderly using high dose ICS. However, 2 subsequent case control studies conducted in 2002 failed to demonstrate any association of diabetes in elderly with either current use of ICS or 3 years uses of ICS.

These study results are subjected to confounding by concurrent systemic corticosteroid usage, lack of long term users of ICS, as well as the effect of other competing causes of diabetes (ie. aging and obesity) being so strong in the elderly that the impact of ICS on the risk of diabetes might have been masked in this particular group of patients.

So far, data is lacking in terms of the association between inhaled corticosteroids and diabetes, as well as impaired glucose tolerance - the pre-diabetic condition. Moreover, the profile of glucose regulation and potential hyperinsulinemia in ICS users with normal glucose tolerance is largely unexplored.

As Asians are at increased risk of developing NIDDM, the effect of ICS in inducing diabetes in the Chinese might be more prominent than that for subjects in the western countries. It is of more clinical significance and relevance to study this issue in a Chinese dominant community like Hong Kong.

Therefore, we shall investigate the effect of ICS, trying to understand its impact on the whole disease spectrum of insulin resistance. We shall begin with study on the risk of diabetes, then move on to that of impaired glucose tolerance (IGT) and finally to explore potential hyperinsulinemia in subjects with normal glucose tolerance who have used ICS. We will also put particular emphasis on the younger Chinese population, where the impact of age and obesity is less marked, and therefore, the effect of ICS on the risk of DM/IGT/ hyperinsulinemia can be better manifested and delineated.

About 10% of our population has asthma and of these, 50% are on long term inhaled corticosteroids. While asthma is not known to cause diabetes and hence not a confounder for the association of ICS and DM, we shall therefore target at the adult Chinese asthma patients using ICS as our study subjects, and compare the risk of diabetes/IGT/hyperinsulinemia of this group of patients with that of the general population.

Since diabetes mellitus is a major health problem that is strongly associated with multiple cardiovascular morbidity and mortality, and inhaled corticosteroid being the most commonly prescribed drug in treating chronic airway diseases, knowledge regarding the risk of DM in association with chronic ICS use will be of major impact on public health.