Sedentary Duration and Systemic Health Burden: Nonlinear Associations with Muscle, Fat, and Vascular Phenotypes in a...

Area of Science:

• Public Health
• Physiology
• Epidemiology

Background:

• Sedentary behavior (SB) is a significant public health issue linked to cardiometabolic risks.
• Limited research exists on the integrated physiological responses of the muscle-fat-vascular system to SB.

Purpose of the Study:

• To investigate the associations between sedentary duration (SD) and key physiological markers: sarcopenic index (SI), fat distribution index (FDI), and pulse pressure index (PPI).
• To explore potential thresholds and effect modifications in these relationships.

Main Methods:

• Retrospective cross-sectional analysis of 13,637 participants from the National Health and Nutrition Examination Survey (2011-2018).
• Self-reported sedentary duration (SD) assessed via questionnaire.
• Multivariable linear regression and restricted cubic spline models used to analyze associations, adjusting for confounders.
• Subgroup analyses conducted to explore effect modification by BMI, sex, race/ethnicity, education, and self-rated health.

Main Results:

• Each additional hour/day of SD was associated with lower SI (β = -0.004) and FDI (β = -0.009), and higher PPI (β = 0.001).
• A nonlinear association between SD and SI was observed, with a critical threshold around 10.73 hours/day.
• Adverse FDI associations were consistent across SD levels, particularly in men and lower education groups.
• Elevated PPI was specifically noted in non-Hispanic Black participants with higher SD.

Conclusions:

• Sedentary duration exhibits differential associations with muscle mass, fat distribution, and vascular function, suggesting a coordinated multisystem response to prolonged sitting.
• Findings support a potential intervention threshold of less than 10.7 hours of daily sedentary time to mitigate physiological risks.