Feeding regulates level of Insulin and IGF-1. These hormones play key role in maintaining blood sugar level. This study proposes that these hormones also act as primary signals of feeding time to body clocks. They reset circadian clocks by induction of period proteins. Any irregular insulin signalling due to untimely eating disrupts circadian physiology and behaviour and clock gene expression. The disruption of body clock in turn is associated with increased incidence of chronic diseases.
Circadian rhythm or our ‘body clock’ is a 24-hour cycle which controls our daily physiological and mental changes including sleep. These body rhythms are responsive to primarily light and darkness in our immediate environment and to our eating time. Physiologically, humans are adapted to receive light and food during daytime. Our body clock is synched well with the external environment. This synchronization is important and that is why whenever there is a major change in our body clock, it can have adverse effects on our health. Example of changes like when someone works night-shift or someone travels across time zones.
It is well known that irregular meal timings, especially eating late in the night may disrupt our body clock leading to poor health, however, the exact mechanism has been unclear until now. A study published in Cell on April 25, 2019 proposes that blood-sugar regulating hormone insulin and insulin growth factors (IGF-1) act as a primary signal which communicate eating time to our body clock. Insulin is normally released when we eat food. In this study, researchers subjected mice to insulin and IGF-1 at a ‘wrong time’ i.e. when it was dark and animals were asleep. Results showed a disruption in mice’s circadian rhythm due to induction of period circadian proteins (PERIOD proteins) at the wrong time when mice didn’t need to be active. The three PERIOD homologous proteins PER1, PER2 and PER3 are the chief components of the mammalian circadian clock. This untimely increase in PER proteins affected mice’s circadian physiology, behaviour and clock gene expression. Mice’s perceived differences between day and night were blurred.
Insulin and IGF-1 have been implicated in affecting body clock in previous studies but their mechanism was not well known. It was thought that their action might be limited to few particular tissues in the body. The factors which hindered establishment of their role was their broad distribution, poor viability and the partial redundancy between insulin and IGF-1.
This new study shows that irregular insulin secretion associated with untimely eating disrupts body’s rhythm and affects one’s health. This disruption of body clock is associated with increased risk and severity of chronic diseases including type 2 diabetes, obesity and cardiovascular ailments. Thus, eating timing and light exposure is important to maintain a healthy body clock. Understanding how our body clock responds and adapts to changes in light and eating time is crucial for night-shift workers, sleep-deprived individuals especially young people and the ageing population.
***
Source(s)
Crosby P. 2019. Insulin/IGF-1 Drives PERIOD Synthesis to Entrain Circadian Rhythms with Feeding Time. Cell. https://doi.org/10.1016/j.cell.2019.02.017
***
