We currently have Harry, an almost two year old who much to Jen’s dismay is still waking regularly in the night to feed. Much of my research stemmed from the birth of our daughter Daisy, and this is the point where my book changed from being a rebuke of dieting, to a full book on the physiology of human metabolism throughout lifespan.
In an attempt to pacify Jen’s upset at seeing other babies sleeping through the night from an early age I turned to my research. And from a metabolic point of view we have a neonate that has previously had 24 hour 7 day a week access to the maternal glucose pool. Upon birth they suddenly have to ask for energy, and over the next period of their life a cry will elicit various reactions from the immediate caregivers, such as checking the nappy, assessing if they are tired, maybe checking their temperature, but of greatest priority are they hungry? So we have to adapt from freely taking energy on demand, to requesting it. This happens regularly due to limited stores of energy, the high demand for glucose (in the womb growth restriction occurs if glucose supply to the brain risks becoming limited, during the early months this may still occur due to limited needs for physical development when the brain must grow and develop prior to learning to crawl, walk, talk etc), and an exceedingly high metabolic rate. (4) So, whilst the lack of ability to sleep through the night may prove frustrating for parents it does provide slower adaption of metabolic rate.
Also, during the night it is critical that your child awakens to feed, they're light sleepers initially due to the need to awaken if they're in danger. Humans are particularly vulnerable and dependent due to limitations in brain size (25% of adult brain volume). This gives rise to the high probability from an evolutionary perspective that infants slept near mothers to be nurtured which brings into question sleep training due to potential psychological damage and raised cortisol levels even when crying has subsided. (5, 6, 7, 8, 9)
And this led to my initial theory that their was a link between cortisol in mother and child. I had initially suspected that this was linked with breast feeding versus non-breast feeding and evidence does suggest this to be the case. (10) And that breast feeding leads to greater resilience to stress, leading to the assumption that small incidences of stress (cortisol) coupled with recovery (feeding, comfort etc) helps the infant develop to deal with the stress of adaption to the external environment. From the perspective of my own research this suggest that the little and often feeding pattern also allows from metabolic adaption to life outside the womb over a longer timescale. (4)
Yet I was interested in the phenomenon that sees my wife awaken prior to Harry (and Daisy when she still breast fed), and this led me to consider cortisol awakening response (CAR). Something my wife probably thinks I made up as I tend to have an answer for everything.
It is well established that the cortisol response we see in adult is not present at birth, but how it is established has been a grey area. and then right when I was seeing this phenomenon occurring with Daisy, a study appeared that showed that infants cortisol levels stay stable upon awakening and then decrease for half an hour afterward. Further to that cortisol levels remained constant following naps. Yet the research team did find a mother-infant cortisol psychological link that confirmed the correlation between mother and infant cortisol levels.
One of the research team stated that,
"In infancy, cortisol responses may be less dependent on hard-wired biological rhythms and more influenced by the HPA axis activity of the baby's immediate caregivers.” (9)
This opens up some fascinating possibilities into our ability to deal with stress in later life, is breast-feeding, the process of feeding regularly, and indeed being at hand to respond to distress (initiating and deactivating the cortisol response) part of a biological process to help us survive in the world? Research suggest that adults that received inconsistent care or mistreatment as a child have high levels of awakening cortisol and dampened response, which does seem to suggest that this bond between mother and child provided a critical role in childhood development. (11, 12)
- Lothian, J, A, PhD. (2005). The Birth of a Breastfeeding Baby and Mother. J Perinat Educ. 14(1): 42–45.
- Leuner, B., Glasper, E, R., and Gould, E. (2010). Parenting and plasticity. Trends Neurosci. 33(10): 465–473.
- Goodwin, M, L, Ph.D. (2010). Blood Glucose Regulation during Prolonged, Submaximal, Continuous Exercise: A Guide for Clinicians. J Diabetes Sci Technol. 4(3): 694–705.
- Craig, B. (2017). Consistent Eating, the metabolic adaption of humans in response to energy restriction. (unpublished)
- Lee T. Gettler, L, T., and McKenna, J, J. (2011). Evolutionary Perspectives on Mother–Infant Sleep Proximity and Breastfeeding in a Laboratory Setting. Am J Phys Anthropol. 144(3): 454–462.
- Bremner, J.D., (1998). The Effects of Stress on Memory and the Hippocampus Throughout the Life Cycle: Implication for Childhood Development and Aging. Developmental Psychology. Fall 10 (4): 871-85.
- Bugental, Daphne Blunt; Martorell, Gabriela A.; Barraza, Veronica (2003). “The hormonal costs of subtle forms of infant maltreatment.” Hormones and Behavior, Vol 43(1), Jan 2003, 237-244.
- Lyons et all. (2000). Stress-Level Cortisol Treatment Impairs Inhibitory Control of Behavior in Monkeys.” J. Neuroscience. October 15. 20 (20):7816–7821.
- Cao, Y., Rao, S, D., Phillips, T, M., Umbach, D, M., Bernbaum, J, C., Archer, J, I., and Rogan, W, J. (2009). Are Breastfed Infants more Resilient?-Feeding Method and Cortisol in Infants. J Pediatr. 154(3): 452–454.
- McEwen, B. S. (2003). Early life influences on life-long patterns of behavior and health. Mental Retardation and Developmental Disabilities Research Reviews, 9(3), 149–154.Bright ,M, A., Granger, D, A., and Frick, J, E. (2012). Do infants show a cortisol awakening response? Dev Psychobiol. 54(7):736-43.
- Carpenter, L, L. Tyrka, A, R., Ross, N, S., Khoury, L., Anderson, G, M., and Price, L, H. (2009). Effect of Childhood Emotional Abuse and Age on Cortisol Responsivity in Adulthood Biol Psychiatry. 66(1): 69–75.
- Doom, J, R., Cicchetti, D., and Rogosch, F, A.(2014). Longitudinal Patterns of Cortisol Regulation Differ in Maltreated and Nonmaltreated Children. J Am Acad Child Adolesc Psychiatry. 53(11): 1206–1215.