Abstract
Asthma is a heterogeneous disease with many phenotypes, and age at disease onset is an important factor in separating the phenotypes. Most studies with asthma have been performed in patients being otherwise healthy. However, in real life, comorbid diseases are very common in adult patients. We review here the emerging comorbid conditions to asthma such as obesity, metabolic syndrome, diabetes mellitus type 2 (DM2), and cardiac and psychiatric diseases. Their role as risk factors for incident asthma and whether they affect clinical asthma are evaluated. Obesity, independently or as a part of metabolic syndrome, DM2, and depression are risk factors for incident asthma. In contrast, the effects of comorbidities on clinical asthma are less well-known and mostly studies are lacking. Cross-sectional studies in obese asthmatics suggest that they may have less well controlled asthma and worse lung function. However, no long-term clinical follow-up studies with these comorbidities and asthma were identified. These emerging comorbidities often occur in the same multimorbid adult patient and may have in common metabolic pathways and inflammatory or other alterations such as early life exposures, systemic inflammation, inflammasome, adipokines, hyperglycemia, hyperinsulinemia, lung mechanics, mitochondrial dysfunction, disturbed nitric oxide metabolism, and leukotrienes.
Highlights
Asthma is a common chronic disorder affecting more than 300 million people all over the world with prevalence among adults varying between 0.2 and 21% [1]
We aim to give the reader an overview of the emerging comorbid conditions to asthma such as obesity, metabolic syndrome (MBO), diabetes mellitus type 2 (DM2), cardiovascular diseases (CVD), and psychiatric diseases (Figure 1)
It is well-known that obesity is associated with a reduction in expiratory reserve volume (ERV) and functional residual capacity (FRC) [53,54,55], but it still remains contradictory, whether obesity or body mass index (BMI) as such is associated with more severe airway obstruction (FEV1/forced vital capacity (FVC)) (see Tables 1(a) and 1(b))
Summary
Asthma is a common chronic disorder affecting more than 300 million people all over the world with prevalence among adults varying between 0.2 and 21% [1]. Most of asthma is thought to start during childhood This has recently been challenged by showing that, in United States, adult-onset asthma is the dominant phenotype in women from 40 years of age [8]. As recently reviewed in this journal [4] the mechanisms of adult-onset asthma may include several metabolic and inflammatory components that are common to the other diseases such as obesity, metabolic syndrome (MBO), diabetes mellitus type 2 (DM2), cardiovascular diseases (CVD), and psychiatric diseases. In real life, comorbid diseases are very common, especially in adult and/ or aging patients. We aim to give the reader an overview of the emerging comorbid conditions to asthma such as obesity, MBO, DM2, CVD, and psychiatric diseases (Figure 1). We have five separate aims in this review if such data is available: (A) to characterize the epidemiological evidence how these comorbidities associate with asthma, (B) to describe the role of the comorbidity as a risk factor for incident asthma, (C) the possible role of asthma as a risk factor for the incident comorbidity, (D) the effect of the comorbidity on the clinical outcome of asthma, and (E) to describe the possible common mechanisms that may link asthma and the abovementioned comorbid conditions
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