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. 2012 Jul 1;35(7):921-32.
doi: 10.5665/sleep.1952.

The interaction of obstructive sleep apnea and obesity on the inflammatory markers C-reactive protein and interleukin-6: the Icelandic Sleep Apnea Cohort

Erna S Arnardottir  1 , Greg Maislin, Richard J Schwab, Bethany Staley, Bryndis Benediktsdottir, Isleifur Olafsson, Sigurdur Juliusson, Micah Romer, Thorarinn Gislason, Allan I Pack
Affiliations

The interaction of obstructive sleep apnea and obesity on the inflammatory markers C-reactive protein and interleukin-6: the Icelandic Sleep Apnea Cohort

Erna S Arnardottir et al. Sleep. .

Abstract

Study objectives: To assess the relative roles and interaction of obstructive sleep apnea (OSA) severity and obesity on interleukin-6 (IL-6) and C-reactive protein (CRP) levels.

Design: Cross-sectional cohort.

Setting: The Icelandic Sleep Apnea Cohort.

Participants: 454 untreated OSA patients (380 males and 74 females), mean ± standard deviation age 54.4 ± 10.6 yr.

Interventions: N/A.

Measurements and results: Participants underwent a sleep study, abdominal magnetic resonance imaging to measure total abdominal and visceral fat volume, and had fasting morning IL-6 and CRP levels measured in serum. A significantly higher correlation was found for BMI than visceral fat volume with CRP and IL-6 levels. Oxygen desaturation index, hypoxia time, and minimum oxygen saturation (SaO₂) significantly correlated with IL-6 and CRP levels, but apnea-hypopnea index did not. When stratified by body mass index (BMI) category, OSA severity was associated with IL-6 levels in obese participants only (BMI > 30 kg/m²). A multiple linear regression model with interaction terms showed an independent association of OSA severity with IL-6 levels and an interaction between OSA severity and BMI, i.e., degree of obesity altered the relationship between OSA and IL-6 levels. An independent association of OSA severity with CRP levels was found for minimum SaO₂ only. A similar interaction of OSA severity and BMI on CRP levels was found for males and postmenopausal women.

Conclusions: OSA severity is an independent predictor of levels of IL-6 and CRP but interacts with obesity such that this association is found only in obese patients.

Keywords: C-reactive protein; Obstructive sleep apnea; interleukin-6; obesity; visceral fat.

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Figures

Figure 1
Figure 1
The study cohort. The selection of the cohort and division into BMI categories.
Figure 2
Figure 2
The range of the apnea-hypopnea index (AHI, upper panel) and oxygen desaturation index (ODI, lower panel) within the 3 BMI categories in all patients considered (A and C) and the selected cohort with AHI 14-80 and ODI 10-65 only (B and D).
Figure 3
Figure 3
Correlation between minimum oxygen saturation (SaO2) and (A) IL-6 levels and (B) CRP levels within the 3 BMI categories.
Figure 4
Figure 4
Three-dimensional plots for IL-6 levels as a function of BMI and 4 OSA severity measures: (A) apnea-hypopnea index (AHI); (B) oxygen desaturation index (ODI); (C) hypoxia time (minutes with SaO2 < 90%), and (D) minimum oxygen saturation (SaO2). The significance of associations between IL-6 levels and sleep apnea severity, obesity and their interaction are shown below the figures. These analyses are not adjusted for other confounders.
Figure 5
Figure 5
Three-dimensional plots for CRP as a function of BMI and 4 OSA severity measures: (A) apnea-hypopnea index (AHI); (B) oxygen desaturation index (ODI); (C) hypoxia time (minutes with SaO2 < 90%); and (D) minimum oxygen saturation (SaO2). The significance of associations between CRP levels and sleep apnea severity, obesity and their interaction are shown below the figures. These analyses are not adjusted for other confounders.
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