How eating feeds into the body clock
April 25, 2019
Science Daily/Medical Research Council
New research has found it is not just what you eat, but when you eat that is important -- knowledge which could improve the health of shift workers and people suffering from jet lag.
The Medical Research Council (MRC)-funded study, published today in the journal Cell, is the first to identify insulin as a primary signal that helps communicate the timing of meals to the cellular clocks located across our body, commonly known as the body clock.
The team behind the research believe this improved understanding may lead to new ways to alleviate the ill-health associated with disruption to the body clock. These could include eating at specific times or taking drugs that target insulin signalling.
The body clock -- also known as the circadian rhythm -- is a 24-hour biological cycle that occurs individually in every cell of the body, driving daily rhythms in our physiology, from when we sleep, to hormone levels, to how we respond to medication. Our body clock is synchronised with the surrounding environment by exposure to daylight and the timing of meals. This synchrony is important for long-term health, and it is well known that disrupting your circadian rhythm by shift work or travel across time zones can be detrimental for health. Importantly, it is thought that eating at unusual times, as often occurrs during shift work and jet lag, is a major cause of body clock disruption. However, it has not previously been known exactly how the body clock senses and responds to meal timing, making it difficult to provide medical advice or interventions that might alleviate the problem.
Researchers at the MRC Laboratory of Molecular Biology (LMB) in Cambridge and the University of Manchester have now identified insulin as a primary signal that helps communicate the timing of meals to the cellular clocks across our body, and in doing so strengthen the circadian rhythm. The team's experiments in cultured cells, and replicated in mice, show that insulin, a hormone released when we eat, adjusts circadian rhythms in many different cells and tissues individually, by stimulating production of a protein called PERIOD, an essential cog within every cell's circadian clock.
Dr John O'Neill, a research leader at the MRC LMB who led the Cambridge research team, said: "At the heart of these cellular clocks is a complex set of molecules whose interaction provides precise 24-hour timing. What we have shown here is that the insulin, released when we eat, can act as a timing signal to cells throughout our body."
Working with Dr David Bechtold, a senior lecturer at the University of Manchester, the researchers found that when insulin was provided to mice at the 'wrong' biological time -- when the animals would normally be resting -- it disrupted normal circadian rhythms, causing less distinction between day and night.
Dr Bechtold said: "We already know that modern society poses many challenges to our health and wellbeing -- things that are viewed as commonplace, such as shift-work, sleep deprivation, and jet lag, disrupt our body clock. It is now becoming clear that circadian disruption is increasing the incidence and severity of many diseases, including cardiovascular disease and type 2 diabetes."
Dr Priya Crosby, a researcher at the MRC LMB and lead author on the study, highlighted: "Our data suggests that eating at the wrong times could have a major impact on our circadian rhythms. There is still work to do here, but paying particular attention to meal timing and light exposure is likely the best way to mitigate the adverse effects of shift-work. Even for those who work more traditional hours, being careful about when we eat is an important way to help maintain healthy body clocks, especially as we age."
https://www.sciencedaily.com/releases/2019/04/190425143607.htm
Effects of night-time light on internal body clock
April 30, 2018
Science Daily/The Physiological Society
New research published in The Journal of Physiology has illuminated the effects of night-time light exposure on internal body clock processes. This is important for helping those who have poor quality sleep, such as shift workers, and could help improve treatments for depression.
The body has an internal clock that causes various physiological processes to oscillate in 24-h cycles, called circadian rhythms, which includes daily changes in sleepiness. Light is the strongest environmental time cue that resets the body's internal 24-h clock. Melatonin is a hormone produced in the brain at night that regulates this body clock and exposure to light before bedtime may reduce sleep quality by suppressing its production. The research team aimed to explore the link between the physiological process that enables our internal body clock to synchronise to external time cues (i.e. day and night) -- called circadian phase resetting -- and suppression of melatonin.
Melatonin suppression and circadian phase resetting are often correlated such that high levels of melatonin suppression can be associated with large shifts of the body clock. This association between the two responses has often been assumed to represent a functional relationship, resulting in the acceptance that one could be used as a proxy measure for the other. Circadian phase resetting is more difficult to measure than melatonin suppression, meaning the latter has often been used to assess disruption to the body clock caused by light exposure at night. However, this research has found that the magnitude of the shift in internal body clock is functionally independent from melatonin suppression. This casts doubt on the use of melatonin suppression as a proxy for circadian phase resetting. This knowledge may shape future research designed to improve treatments for depression and shift work sleep disorder.
The researchers tested the association between melatonin suppression and circadian phase resetting in participants who received either continuous or intermittent bright light exposure at night. This research procedure involved each participant completing a 9-10 day inpatient study at Brigham and Women's Hospital, Boston, under highly controlled laboratory conditions with strict control over their sleep/wake, activity and light/dark schedules. Intermittent exposure patterns were found to show significant phase shifts with disproportionately less melatonin suppression. Moreover, each and every intermittent bright light pulse induced a similar degree of melatonin suppression, but did not appear to cause an equal magnitude of phase shift.
Despite the results of this study suggesting functional independence in circadian phase resetting and melatonin suppression responses to exposure to light at night, the study's conclusions may be restricted by the limited sample size in each light exposure condition.
Lead author Dr Shadab Rahman is excited by his team's findings, and is looking forward to investigating new avenues of interest they have opened up:
"Overall, our data suggest that melatonin suppression and phase resetting are sometimes correlated, but ultimately are regulated by separate neurophysiological processes. Therefore melatonin suppression is not a reliable surrogate for phase resetting. This is an important consideration for developing light-therapy treatments for people who have poor quality sleep and biological clock disruption, such as shift workers, or disorders such as depression. Additional work is needed to optimize light therapy protocols used as treatment."
https://www.sciencedaily.com/releases/2018/04/180430075635.htm
Light exposure linked to weight gain in children
October 23, 2015
Science Daily/Queensland University of Technology
A world-first study has revealed pre-schoolers exposed to more light earlier in day tend to weigh more. She says the research suggests light exposure, artificial and natural, needs to be part of the conversation about the weight of children, along with calorie intake, decreased physical activity and sleep patterns.
http://images.sciencedaily.com/2015/10/151023105914_1_540x360.jpg
Ms Pattinson said it is known the timing, intensity and duration of exposure to both artificial and natural light have acute biological effects in mammals. (Stock image of normal healthy child)
Credit: © Sabphoto / Fotolia
Cassandra Pattinson, a PhD student and her colleagues studied 48 children aged three to five from six Brisbane childcare centres over a two week period, measuring each child's sleep, activity and light exposure along with their height and weight to calculate their BMI.
"We found moderate intensity light exposure earlier in the day was associated with increased body mass index (BMI) while children who received their biggest dose of light -- outdoors and indoors -- in the afternoon were slimmer," said Ms Pattinson who will present her findings at the ASA Sleep Downunder Conference in Melbourne on 23 October.
"Surprisingly physical activity was not associated with the body mass of the children but sleep timing and light exposure was. This is the first time light has been shown to contribute to weight in children.
"With an estimated 42 million children around the globe under the age of five being classified as overweight or obese, it is a significant breakthrough and a world-first.
"Thanks to artificial lighting, including light given off by tablets, mobile phones, night lights, and television, modern children are exposed to more environmental light than any previous generation. This increase in light exposure has paralleled global increases in obesity."
The research team, from QUT's Institute of Health and Biomedical Innovation, worked with the Centre for Children's Health Research
Ms Pattinson said it is known the timing, intensity and duration of exposure to both artificial and natural light have acute biological effects in mammals.
"The circadian clock -- also known as the internal body clock -- is largely driven by our exposure to light and the timing of when that happens. It impacts on sleep patterns, weight gain or loss, hormonal changes and our mood," Ms Pattinson said
"Recent research in adults suggests exposure to light later in the day is associated with increased body mass, but no studies had investigated these effects in young children and it turns out it has the opposite effect.
"While adults who take in more morning light are slimmer, pre-school children exposed to morning light tend to be heavier.
"Factors that impact on obesity include calorie intake, decreased physical activity, short sleep duration, and variable sleep timing. Now light can be added to the mix."
Ms Pattinson said the next step was to figure out how the research can be used in the fight against obesity in children.
"We plan to conduct further studies with pre-schoolers and also infants," she said.
"Animal studies have shown that timing and intensity of light exposure is critical for metabolic functioning and weight status. Our findings suggest that the same applies to us.
"This research suggests that exposure to different types of light at different times now needs to be part of the conversation about the weight of children."