Background: This study tested if the timing of meals, physical activity, light exposure, and sleep cluster within individuals and are associated with body mass index (BMI) in a sample of free-living adults (N = 125). Methods: Data were collected between November 2015 and March 2016 at the University of California, San Diego, Children’s Hospital of Philadelphia, and Washington University in St Louis. Height and weight were measured, and BMI (kg/m2) was calculated. Sleep timing was estimated using actigraphy, and timing of meals, physical activity, and light exposure were self-reported using a smartphone application. General linear models estimated the mean BMI across time categories of behaviors, adjusting for covariates. A latent class analysis was used to identify patterns of timing variables that clustered within individuals and test for associations between identified patterns and BMI. Results: Later exposure to outdoor light was associated with a lower BMI (P trend < .01). The timing of other behaviors was not independently associated with BMI. The latent class analysis identified 2 distinct groups related to behavioral timing, reflecting an “early bird” and “night owl” phenotype. These phenotypes were not associated with BMI (P > .05). Conclusion: Timing of exposures to light, meals, sleep, and physical activity were not strongly associated with BMI in this sample.
Catherine R. Marinac, Mirja Quante, Sara Mariani, Jia Weng, Susan Redline, Elizabeth M. Cespedes Feliciano, J. Aaron Hipp, Daniel Wang, Emily R. Kaplan, Peter James and Jonathan A. Mitchell
Sheri J. Hartman, Catherine R. Marinac, Lisa Cadmus-Bertram, Jacqueline Kerr, Loki Natarajan, Suneeta Godbole, Ruth E. Patterson, Brittany Morey and Dorothy D. Sears
Background: Sedentary behavior is associated with increased risk of poor outcomes in breast cancer survivors, but underlying mechanisms are not well understood. This pilot study explored associations between different aspects of sedentary behaviors (sitting, prolonged sitting, sit-to-stand transitions, and standing) and breast cancer risk-related biomarkers in breast cancer survivors (n = 30). Methods: Sedentary behavior variables were objectively measured with thigh-worn activPALs. Breast cancer risk-related biomarkers assessed were C-reactive protein (CRP), insulin, and homeostatic model assessment of insulin resistance (HOMA-IR) and were measured in fasting plasma samples. Linear regression models were used to investigate associations between sedentary behavior variables and biomarkers (log CRP, insulin, and HOMA-IR). Results: Sit-to-stand transitions were significantly associated with insulin resistance biomarkers (P < .05). Specifically, each 10 additional sit-to-stand transitions per day was associated with a lower fasting insulin concentration (β = −5.52; 95% CI, −9.79 to −1.24) and a lower HOMA-IR value (β = −0.22; 95% CI, −0.42 to −0.03). Sit-to-stand transitions were not significantly associated with CRP concentration (P = .08). Total sitting time, long sitting bouts, and standing time were not significantly associated with CRP, insulin, or HOMA-IR (P > .05). Conclusions: Sit-to-stand transitions may be an intervention target for reducing insulin resistance in breast cancer survivors, which may have favorable downstream effects on cancer prognosis.