Shift Work and Clinical Applications of Time-Restricted Eating

Abstract

Circadian rhythms refer to the oscillations of biological systems in synchrony with the 24-hour light/dark (LD) cycles of the earth. Mammalian circadian rhythms are coordinated by an array of endogenous “clocks” entrained by environmental inputs (zeitgebers), such as sunlight, locomotion, and food intake. Physiological states including energy balance, sleep-wake cycles, body temperature, and hormonal homeostasis, are all tightly regulated by endogenous circadian clocks. The primary controller of circadian rhythms is located centrally in the Suprachiasmatic Nuclei (SCN) of the hypothalamus, which is directly entrained by UV light signals coming from the sun. Peripheral circadian rhythms are directly modulated by behaviors such as locomotion and feeding behavior. A lack of coordination between the LD cycles of earth and behavioral activity results in systemic perturbations, ultimately resulting in metabolic dysfunction. This lack of coordination is likely responsible for the elevated prevalence of metabolic syndrome observed in night-shift workers, due to the misalignment of their activity patterns with the LD cycles of earth. The common trend of night-shift workers adopting a schedule of 3 days on, 4 days off followed by 4 days on, 3 days off may be the biggest driver of their increased risk of developing metabolic dysfunction. By constantly rotating between a nocturnal and diurnal sleeping pattern, their central and peripheral clocks fall into a state of perpetual arrhythmicity. While this type of schedule is provided to maintain social normalcy for the individual, it is detrimental to the functional rhythmicity of their circadian clocks. For this reason, night-shift workers may enact a time-restricted eating protocol in which food intake is restricted to a limited window of time every day. While disruption of the central circadian clock in the SCN is inevitable due to nighttime blue light exposure in these workers, maintaining a highly consistent feeding pattern may attenuate in part the negative consequences of such exposure by restoring rhythmicity in peripheral clocks. This type of feeding strategy may also be exploited by non-night shift workers, as the ubiquity of technology inevitably results in chronic blue light exposure during the intended dark phase of many humans in modern society. In doing so, circadian rhythmicity of key metabolic factors may be restored, thereby optimizing metabolic health and limiting the risk of developing chronic disease.