This post started with a deep dive into the literature surrounding circadian rhythm alteration and implications for adrenal function. As I started to get a more clear understanding of the different patterns associated with daytime and night time, the next logical question for me was: what happens when we are awake during night time hours? And what happens when we eat during the times we are supposed to be asleep? These questions led me into some of the research literature on shift work. I’ve summarized my research into this topic below and included some simple, practical suggestions for all my awesome shift workers!! Please DM me and let me know what things work for you and what things don’t! I am super fascinated by this research and even more curious with how we can leverage what we know about our circadian clocks to help our bodies adapt to this stressor!
Some of what we know:
- We have central and peripheral “clocks” otherwise known as “oscillators.” The central clock is located in the suprachiasmatic nucleus (SCN) in hypothalamus. Light is the most potent stimulator of this clock. Light entering the SCN is responsible for a cascade of metabolic and hormonal events that occur during day time. The absence of light is the trigger for the cascade of events that occur at night (Baron & Reid, 2014).
- We also have peripheral circadian clocks in our organs (including liver, muscle, and adipose tissue)- 10% of the genes in any given organ exhibit circadian clocks (Scheer, et al, 2009). One of most potent stimulator of these peripheral clocks is food.
- In humans, a 12-hour shift of the sleep/ wake cycle and fasting/ feeding cycle compared with the central circadian system (while maintaining an isocaloric diet) reduced glucose tolerance, increased blood pressure, and decreased levels of leptin (Scheer, et al., 2009). Leptin can be thought of our satiety hormone- elevations in this hormone lead to feelings of fullness or “satiety.” Even after short term disruptions in circadian rhythms (as short as 8 days), humans demonstrate elevated blood glucose, elevated insulin, and elevated blood pressure (Koch, Leinweber, Drengberg, Oster, 2017)
- Humans are predisposed to the promotion of glucose metabolism and fat storage during the day time (when we normally eat) and glucose sparing and fat metabolism at night (when we normally fast). We also know that sleep deprivation can lower glucose tolerance (Lowden, 2010)
- Studies demonstrate that sleep restriction in humans results in altered circulating levels of our satiety hormone, leptin. It is thought that alterations in the neurohormonal control of appetite could be a contributing factor to weight gain associated with circadian disruption and shift work. Night shift workers also have significantly decreased melatonin levels and elevated cortisol levels which have been shown suppress leptin (Ferrell and Chiang, 2015). Circadian rhythm misalignment has also been found to increased levels of ghrelin (hunger hormone) after meals in addition to increasing appetite for energy dense foods.
Alterations in our natural patterns of sleep/ wake times and fasting/ feeding cycles have wide ranging impacts on our physiology. I think this is important information for those of us who do shift work to be aware of. One concept that I consider often when working with clients is optimizing vs. adapting. When we are living a lifestyle that requires us to be awake during our normal sleeping hours, we are living more in the land of adapting to that stimulus as opposed to optimizing function. This does not mean that we cannot make progress, but it does mean that appetite, energy regulation, and potentially body composition may not be as great as if we were operating within our body’s natural sleep/ wake cycle.
Considerations based on the research:
- Focus on consuming balanced meals with all macros (pro, carb, fat) and be sure to have an adequate fiber at each meal to help avoid any spikes/ dips in blood glucose. Research is consistent in demonstrating that shift workers are at a greater risk for metabolic syndrome, so keeping tabs on blood glucose regulation seems prudent.
- Focus on consuming a nutrient dense diet. With dysregulation of hunger/ satiety hormones, consider avoiding hyperpalatable foods- as they are designed to make you eat more and more of them and generally they provide very little nutrient value. Prepare nutrient dense meals for work so you have awesome food choices available. Consider tracking your intake in @cronometer_official to keep tabs on any vitamin/ mineral deficits so you can alter your dietary habits or supplement accordingly.
- Dedicate 12 hrs/ day to fasting (just as you would if you were sleeping during the night)- experiment here and see what window of time works best for you. Have scheduled meal times during your work days and your off days to help keep as much consistency as possible.
- Get sunlight or bright light in your eyes early in the day if you want to advance your circadian rhythm (aka go to sleep earlier) and sunlight or bright light later in the day if you want to delay your circadian rhythm (aka go to sleep later).
- Be protective of your sleep!! Get at least 8 hours/ day. Invest in blackout curtains, ear plugs, white noise machines, etc to ensure that you can crush some high quality sleep.
- Develop a consistent exercise schedule. With the increased risk of metabolic syndrome associated with shift work- staying active is super important. I would also add that your risk of over-training/ under-recovering is higher so tread carefully with exercise volume/ intensity.
- Understand that shift work requires alterations in your body’s circadian rhythms. It will likely take 2-3 days to adjust back to your normal day time schedule after working a few nights in a row. Be kind to yourself and give your body to make the adjustments necessary between work periods. Having a dedicated schedule for both work days and off days will likely help make the transition easier.
Sample schedule for 12-hour night shift
Meal 1 4pm (light meal, pre-workout)
Meal 2 630pm
Meal 3 11pm
Meal 4 2pm
Meal 5 4am or 5am
(Fasting window 5am-4pm)
Straif K, Baan R, Grosse Y, Secretan B, Ghissassi FEL, Bouvard V, et al. Carcinogenicity of shift-work, painting, and firefighting. Lancet Oncol. 2007;8:1065–6
Scheer, et al (2009). Adverse metabolic and CV consequences of circadian misalignment. Proc Natl Acad Sci USA, 106(11): 4453-4458
Lowden (2010). Eating and shift work- effects on habits, metabolism, and performance. Scand J Work Environ Health, 36(2): 150-162.
Koch, Leinweber, Drengberg, Oster (2017). Interaction between circadian rhythms and stress. Neurobiology of Stress, 57-67.
Chung, Soon, Kim (2011). Circadian rhythm of adrenal glucocorticoid: Its regulation and clinical implications. Biochimica et Biophysica Acta, 581-591.
Ferrell and Chiang (2015). Circadian rhythms in liver metabolism and disease. Acta Pharmaceutica Sinica B, (5)2, 113-122.
Wang F, et al (2014), Night shift work and metabolic syndrome. Obes Rev, 15: 709-720.
Qian et al (2018). Ghrelin is impacted by the endogenous circadian system and by circadian misalignment in humans. Int J of Obesity.
Bacon & Reid (2014). Circadian misalignment and Health. Int Rev Psychiatry, 26(2).