Compositional isotemporal substitution analysis of physical activity, sedentary behaviour and cardiometabolic biomarkers in US adults: A nationally representative study

Substantial evidence links physical activity and sedentary behaviour (SB) with cardiovascular health. However, studies usually examine time-use behaviours independently, rather than considering daily activities as a 24-hour time-use composition. This study aimed to use compositional data models to investigate how time reallocations from SB to moderate-to-vigorous physical activity (MVPA)/ light physical activity (LPA) were associated with changes in cardiometabolic biomarkers. Compositional isotemporal substitution analysis was conducted using data from a representative cross-sectional sample of adults aged 20 years or older (n = 5213 full sample; n = 2221 fasting subsample) from the 2003-2004 and 2005-2006 cycles of the National Health and Nutrition Examination Survey. Overall as well as gender- and age-specific estimates were obtained for reallocating time between the behaviours associated with cardiometabolic outcomes. Replacing SB with MVPA was associated with decreased levels of C-reactive protein (CRP), white blood cells (WBCs), red blood cell distribution width (RDW), insulin, insulin resistance homeostasis model assessment (HOMA-IR) and 2-hour glucose, and increased high-density lipoprotein cholesterol (HDL-C), except for WBCs in older adults, insulin and HOMA-IR in females and older adults, 2-hour glucose in young and older adults, and HDL-C in older adults. Substituting LPA for SB resulted in lower CRP in older adults, lower RDW in males and older adults, lower insulin in young and middle-aged adults, lower HOMA-IR in females and middle-aged adults, and higher HDL-C in males and young adults. Our findings provide new evidence for the potential benefits of LPA and MVPA in cardiovascular health and help make population-specific recommendations for physical activity.