Isotemporal Substitution of Time Between Sleep and Physical Activity: Associations With Cardiovascular Risk Factors in Early Rheumatoid Arthritis

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Abstract
Objective: We aimed to determine relationships between objectively measured nightly sleep, sedentary behavior (SB), light physical activity (LPA), and moderate to vigorous physical activity (MVPA) with risk factors for cardiovascular disease (CVD) in patients with early rheumatoid arthritis (RA). Furthermore, we aimed to estimate consequences for these risk factors of theoretical displacements of 30 minutes per day in one behavior with the same duration of time in another.Methods: This cross‐sectional study included 78 patients with early RA. Nightly sleep, SB, LPA, and MVPA were assessed by a combined heart rate and accelerometer monitor. Associations with risk factors for CVD were analyzed using linear regression models and consequences of reallocating time between the behaviors by isotemporal substitution modeling.Results: Median (Q1‐Q3) nightly sleep duration was 4.6 (3.6‐5.8) hours. Adjusted for monitor wear time, age, and sex, 30‐minutes‐longer sleep duration was associated with favorable changes in the values β (95% confidence interval [CI]) for waist circumference by −2.2 (−3.5, −0.9) cm, body mass index (BMI) by −0.9 (−1.4, −0.4) kg/m2, body fat by −1.5 (−2.3, −0.8)%, fat‐free mass by 1.6 (0.8, 2.3)%, sleeping heart rate by −0.8 (−1.5, −0.1) beats per minute, and systolic blood pressure by −2.5 (−4.0, −1.0) mm Hg. Thirty‐minute decreases in SB, LPA, or MVPA replaced with increased sleep was associated with decreased android fat and lower systolic blood pressure levels. Replacement of SB or LPA with MVPA yielded lower BMIs.Conclusion: Shorter sleep during the night is common among patients with early RA and is associated with adverse risk factors for CVD.

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