PURPOSE: Previous studies have linked increased levels of BMI with poorer asthma outcomes. However, there is considerable debate about the causal direction and mechanisms linking the two diseases. The purpose of this study was to assess the impact of baseline levels of asthma control and BMI on future levels of asthma control and BMI.
METHODS: A total of 352 patients, recruited from a tertiary care asthma clinic in Montreal completed baseline and follow-up interviews. At baseline, patients provided demographic, medical and height and weight information (to calculate BMI), and completed the Juniper Asthma Control Questionnaire (ACQ). The same information was collected via telephone interview an average of 4.4 years later. General linear model analyses were conducted adjusting for baseline age, sex, asthma severity, change in smoking status, time of follow-up, and the baseline value of the dependent variable.
RESULTS: There was a main effect of baseline asthma control on 4-year BMI (Beta (SE)=0.435 (0.198), p=.029), such that poorer control was associated with greater increases in BMI. In contrast, there was no main effect of baseline BMI on 4-year asthma control (Beta (SE)=-0.001 (0.011), p=.937). Additional analyses assessing any potential mediational role of sex found no significant interaction between sex and asthma control on BMI (F=0.00, p=.985), nor of BMI on asthma control (F=0.05, p=.823).
CONCLUSIONS: Poorer asthma control at baseline was associated with an increase in BMI over 4 years, whereas baseline BMI was not associated with an increase in asthma control over the same period. This suggests that in tertiary care asthma patients, the BMI-asthma relationship is driven by asthma symptomatology. Though the current study did not assess causal mechanisms, there are several behavioural and physiological pathways which could explain this finding, which should be the focus of future research.
CLINICAL IMPLICATIONS: Patients with poor asthma control may be at increased risk of gaining weight, which may lead to obesity and the development of other weight-related chronic conditions (e.g., diabetes). Targeting these patients for weight management interventions may prevent future complications.
DISCLOSURE: The following authors have nothing to disclose: Simon Bacon, Karine Ouellet, Ariane Jacob, Catherine Lemiere, Kim Lavoie
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