PROJECT SUMMARY
Despite global improvements in cardiovascular disease (CVD) rates, CVD morbidity and mortality are
increasingly common in young adults aged 18 to 39. CVD research often excludes younger individuals, resulting
in prevention strategies that are tailored to older populations, as well as algorithms that underestimate young
adult CVD risk and clinical guidelines that systematically undertreat young patients. Scientific consensus
indicates that CVD risk begins to accumulate in early life, with vulnerabilities and behaviors in early adulthood
determining the lifelong trajectory of cardiovascular health. Therefore, prevention strategies that target novel
primordial indicators (i.e., early vulnerabilities emerging prior to traditional CVD risk factors) are urgently needed
to prevent or delay CVD progression in young adults. The American Heart Association’s Life’s Essential 8
guidelines emphasize sufficient amounts of physical activity (PA; ≥150 min/week moderate-to-vigorous physical
activity [MVPA]) and sleep (≥7 h/night) as core CVD prevention strategies. However, the majority of young adults
fail to reach these recommended levels. These guidelines also draw from an evidence base that considers PA
and sleep behaviors in isolation from their inherent compositional and circadian characteristics which might also
affect cardiovascular health. Other weaknesses in the extant literature—including the use of inaccurate self-
report measures and primarily cross-sectional examinations of aggregated PA/sleep on end-stage CVD
outcomes—provide an incomplete understanding of the relationship between PA/sleep and CVD. Therefore, this
training grant will examine the longitudinal, objectively-measured, within-person effects of compositional 24-h
behaviors (light PA [LPA], MVPA, sedentary behavior [SB], sleep) and circadian rhythm on two primordial CVD
indicators (stress, fatigue) in a cohort of free-living young adults. Data from N=239 participants in the recently-
completed TIME Study will be utilized. 24-h behaviors and circadian rhythm were continuously measured with
wrist-worn accelerometers (Fossil Sport smartwatches), and stress and fatigue were collected with daily
ecological momentary assessment (EMA) prompts, over the course of one calendar year. We will then apply a
series of novel combined multilevel model/isotemporal substitution analyses to examine within-person main
effects of 24-h behavior compositions and circadian rhythm metrics on daily stress and fatigue, while controlling
for between-person effects. The potential moderating effects of relative prior-day sleep deprivation, inactivity,
and sedentariness, and current-day circadian rhythm metrics, will also be examined on these relationships. To
our knowledge, this is the first largescale intensive longitudinal study to examine the within-person compositional
effects of 24-h behaviors and circadian rhythm on early indicators of CVD risk in young adults. Our findings will
help inform the development of primordial prevention efforts and integrated, tailored behavioral guidelines that
address how unique individuals might decrease sub-clinical CVD risk in the context of their everyday lives.
