Dr. Michael DeSanctis, PhD, LP, ABPP, DBSM, Licensed Psychologist April 2021
What price do we pay for irregular sleep-wake patterns and circadian clock mistiming? One cost is an unhappy and dysregulated gut. Our central circadian clock, residing in a concentration of cells in the hypothalamus of our brain and referred to as the suprachiasmatic nucleus, engages in cross-talk with all our peripheral organs, including the liver and gastrointestinal tract. This communication occurs along hormonal and neural pathways with signaling playing an important role in our mental and physical wellbeing. The gut operates on a daily rhythm just like our alertness, energy and cortisol levels, cardiac output, and other vital functions.
Our relentless shift from daylight to darkness and back provides a set of cues for waking, eating, walking, talking, motor movements and resting. Melatonin is the sleep hormone produced by the pineal gland when darkness descends and impacts our suprachiasmatic master clock. What may be less well known, in response to ambient darkness Melatonin is further secreted by neuro-endocrine cells in our gut and contributes to gut health, digestion, and gastric motility. Serotonin, a neuro-transmitter found in the brain, is also secreted in the gut cells along with Ghrelin and other hormones that regulate our digestive process and modulate satiety and hunger. Clock genes do exist in cells of the GI tract and are clearly responsive to encoding of light and dark cycling. An excellent review of circadian physiology and GI interface is found in Konturek, P.C., Brzozowski, T. & Konturek, S.J. (2011).
Our GI tract is part of a primitive nervous system called the enteric nervous system. I use the adjective primitive loosely because the gut possesses intrinsic and ancient intelligence found in our other organ systems. While we may dwell on the power and wisdom inherent in our brain and its hormones/neurotransmitter interplay to maintain mental stability and wellness, the truth is that the less celebrated gut is a vital part of this overall health equation. Essentially, our gut system takes bulk food and reduces it to tiny molecules used for energy expenditure, and all other activities of life. This complex chain of events is vulnerable to disruption in so many ways. As experience tells us, psychological stress, whether situational or chronic, embedded in our ruminations, images, irrational thoughts or decisions, can adversely impact this process along with environmental changes, business or recreational travel, jet lag, changes in life tempo, dietary modifications, and medication to cite just a handful of factors. Conversely, GI disturbance can deliver acute or chronic aches and pain, indigestion, and disorders of elimination, stopping us in our tracks.
Insufficient, fragmented and delayed sleep onsets in the 24-hour day undermine our circadian timing. This disrupted sleep pattern, unhinged from our normal inner clock process, may inappropriately stimulate appetite and encourage hedonic, self-soothing eating patterns well after the dinner hour. What is particularly pernicious is the additive impact of sedentary lifestyles and reduced energy utilization during waking hours. This sequence of events can alter glucose metabolism, complicate weight management and place one at risk for obesity, Type 2 diabetes and GI ailments. Obese individuals may have different levels of Ghrelin versus slim body types and a different 24-hour circadian pattern. Dr. Eve Van Cauter of the University of Chicago and others (Knutson, Spiegel, Penev & Van Cauter (2007) have researched the relationships of hedonic eating, circadian disruption and glucose metabolism. The principle is respecting our system and facilitating balance by choosing activities such as meals, that are appropriate for a given interval in the 24-hour period. There is also ongoing scientific inquiry into the bi-directional relationship of our gut microbiome or bacterial flora and circadian timing of gut processes.
Chronobiological research suggests clock rhythms are inherent in all forms of life, so why would our resident GI microbiota be any different? (cf. Lopez, Lashinger, Weinstock & Bray (2021).
Midnight for a lark, a habitual morning person, well past the usual bedtime, is probably no time for a heavy, acidic meal. There is subsequent, counter-productive recruitment of a prolonged digestive process as we lay in bed hoping to fall asleep. Similarly, it would be ill-advised for a lark to sleep in until late morning and remain sedentary, a period of time when the gut is sensitive to muscle movement and actively promoting the elimination of wastes. For night owls, the optimal evening mealtime and morning awakening time will be shifted forward, perhaps by an hour or two, consistent with the circadian clock and fostering self-regulation.
Synchronizing our circadian clock with external time cues, through routine and appropriate exposures to natural light and darkness, and striving for sufficient, restorative sleep (7-8 hours nightly for adults), can be protective of our gut and promote functional connections between our neural networks, hormones and internal flora, maintaining optimal rhythmicity at the cellular and macro levels. The gut and mind are inseparable. Trusting and honoring our gut feelings form a pathway to understanding our dysregulated body clock- the gut provides a plethora of information about the long and deep reach of our circadian rhythms and the efficiency and effectiveness of our wellness habits.
Knutson, K.L., Spiegel, K., Penev, P. & Van Cauter, E. (2007). The metabolic consequences of sleep deprivation. Sleep Medicine Reviews, 11(3), 163-178. doi: 10.1016/j.smrv.2007.01.002
Konturek, P.C., Brzozowski, T. & Konturek, S.J. (2011). Gut clock: implications of circadian rhythms in the gastrointestinal tract. J. PhysiolPharmacology, April 62(2), 139-50.
Lopez, D.E.G., Lashinger, L.M., Weinstock, G.M., & Bray, M.S. (2021). Cell Metabolism, Mar 24; S1550-4131 (21) 00122-4 doi: 10.1016/j.cmet.2021.03.015 (online, ahead of print)