Abstract
BackgroundAsthma is a chronic inflammatory respiratory disorder associated with reduced lung function and poor quality of life. The condition is also associated with poor self-rated health, a major predictor of objective health trajectories. Of biological correlates to self-rated health, evidence suggests a role for inflammatory cytokines and related sickness behaviours. However, this is mainly based on cross-sectional data, and the relation has not been investigated in patients with chronic inflammatory conditions.ObjectiveTo investigate inflammatory cytokines, lung function, sickness behaviour and asthma-related quality of life as determinants of self-rated health in patients with asthma, and to investigate if these variables co-vary over time.MethodsPlasma cytokines (IL-5, IL-6), lung function (FEV1), sickness behaviour, asthma-related quality of life and self-rated health were assessed in 181 patients with allergic asthma aged 18–64 years in a one-year longitudinal study. Mixed effect regression models and Spearman’s correlation were performed to analyse the associations between repeated measurements.ResultsMore sickness behaviour and poorer asthma-related quality of life were associated with poorer self-rated health (p’s<0.001). In men, both low and high levels of interleukin (IL)-6 and poorer lung function were related with poorer self-rated health (p’s<0.05). Over the year, improved asthma-related quality of life was associated with better self-rated health (Spearman’s rho = -0.34 women,-0.36 men, p’s<0.01). Further, if sickness behaviour decreased, self-rated health improved, but only in women (Rho = -0.21, p<0.05). Increased FEV1 in men was associated with an increase in IL-6 (Rho = 0.24, p<0.05) as well as improved self-rated health (Rho = -0.21, p<0.05) and asthma-related quality of life (Rho = 0.29, p<0.01) over the year.ConclusionThe study highlights the importance of subjectively perceived sickness behaviour and asthma-related quality of life together with lung function as determinants of self-rated health in asthmatic patients. The importance of inflammatory activation for patient reported outcomes in chronic inflammatory conditions need further investigation.
Highlights
Patient reported outcomes (PROMs) such as self-rated health and quality of life, reported directly by the patients without interpretation of anyone else, are becoming increasingly used in clinical practice
The study highlights the importance of subjectively perceived sickness behaviour and asthma-related quality of life together with lung function as determinants of self-rated health in asthmatic patients
Poor self-rated health and poor quality of life have been associated with higher levels of pro-inflammatory cytokines such as interleukin (IL)-6 and tumour necrosis factor (TNF)-alpha in general populations and primary care patients [4,5,6,7]
Summary
Patient reported outcomes (PROMs) such as self-rated health and quality of life, reported directly by the patients without interpretation of anyone else, are becoming increasingly used in clinical practice. Asthma is further associated with poor self-rated health [12] and poor asthma-related quality of life in a way which cannot fully be explained by objective measures of reduced lung function [13]. Of biological correlates to self-rated health, evidence suggests a role for inflammatory cytokines and related sickness behaviours. This is mainly based on cross-sectional data, and the relation has not been investigated in patients with chronic inflammatory conditions. Mixed effect regression analysis using identity as random effect with time as a dummy variable was used to test if self-rated health, sickness behaviour, asthma-related quality of life, inflammatory cytokines or FEV1 (% predicted) changed during the course of the study. A univariate cubic regression spline model with three degrees of freedom and an alpha-level of 0.05 was used explorative to test for linearity in the associations between IL-5 and IL-6 and patient reported outcomes [36]
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