The impact of circadian misalignment and inadequate sleep duration on cardiovascular health in older adults : what can we learn from night shift workers?

Abstract

Abrupt work schedules, such as nightshifts, are prevalent nowadays and are known to cause circadian misalignment and sleep disruption which can have adverse health consequences. Among the well documented pathologies among night workers are cardiometabolic impairments, the effects of which appear to be more disruptive in older adults due to their poorer adaptation to night work schedules. The physiological mechanisms by which night shift work and sleep disruption contribute to increased cardiovascular disease (CVD) risk are poorly understood. Furthermore, the potential role of specific CVD risk biomarkers, such as cardiac troponin I (cTnI) and lipoprotein (a) [Lp(a)], in senior night shift workers remains elusive. Therefore, the aim of the present study was two fold: 1) understand whether transitioning from day work to night work would alter the serum profile of cTnI and Lp(a), and 2) test whether the circadian realignment of work/sleep schedules using a non-invasive combined treatment protocol, consisting of scheduled evening sleep and light exposure, would improve or affect the serum levels of the selected CVD variables. Serum samples of 18 human subjects (67% men; average age 57.2 ± 3 .8 years) were provided by the Division of Sleep and Circadian Rhythm Disorders - Harvard Medical School/Brigham and Women's Hospital and were analyzed for cTnI and Lp(a) levels, collected at 0700 AM, using ELISA. These subjects had undergone a 10-day rotating shift work schedule: 4 day shifts followed by 3 night shifts. Before starting the night shifts, they were randomized into 2 groups: control (group A), allowed to sleep ad libitum following the night shift and was exposed to typical indoor lighting, and combined treatment (group B), maintained on an 8h sleep schedule and was exposed to enhanced lighting during the three night shifts. In group A, there was no difference in the average serum concentration of cTnI between the end of dayshift work and the last day of night shift work. In group B; however, combined treatment resulted in a significant reduction in serum cTnI at the end of the night shift compared to dayshift period (0.147 ± 0.097 ng/mL vs 0.295 ± 0.208 ng/mL, p=0.046). The serum concentration of Lp(a) did not significantly change after the transition from day to night work in either group. In addition, a significant negative correlation was found between BMI and cTnI after the night shifts (rs=-0.51, p=.04, N=16). However, no correlation was found between cTnI and either of cortisol or sleep duration. As for Lp(a), no correlation was found between Lp(a) and either of BMI, cortisol, or sleep duration. We conclude that a combined treatment protocol consisting of scheduled evening sleep and enhanced lighting is a promising non-invasive, cost-effective prophylactic approach with possible cardioprotective effects, especially among high risk population groups like older adult nightshift workers. The benefits of such behavioral and/or photic interventions on lowering the risk of cardiovascular morbidity and enhancing the quality of life in elderly nightshift worker requires further investigation.