A window into maternal health through hair cortisol
By Tony Liu
In the field of psychiatry, in which concrete physiological measurements that inform diagnosis and treatment are limited, measurement of hair cortisol concentration (HCC) is a promising tool. Cortisol is a critical hormone in the body’s stress response system, and cortisol in the bloodstream is steadily deposited into hair over time. The cortisol levels in the first centimeter of hair closest to the scalp reflect body cortisol levels during the most recent month, and segments further away from the scalp contain cortisol levels from successive previous months. Consequently, chemical measurements of hair cortisol offer a rare, non-invasive window into the body’s past hormonal dynamics.
During pregnancy, women experience significant changes in their cortisol levels, as the placenta’s developing hormonal system triggers the increased production of maternal cortisol. Alterations in these cortisol dynamics could have important effects on maternal and fetal health, and their impact on preterm birth and postpartum depression are under active investigation. However, cortisol can be challenging to measure due to its circadian fluctuations; analysis of HCC is a method that might overcome this problem.
Unfortunately, recent studies and meta-analyses have yielded mixed evidence regarding the ability of HCC to measure the increases in cortisol across gestation. Further, the association of cortisol levels with mothers’ psychosocial stress levels is still unclear.
The study in Comprehensive Psychoneuroendocrinology, published by Dr. Lucy King, a former Ph.D. student under the supervision of Dr. Ian Gotlib in Stanford’s Department of Psychology, investigates the dynamics of HCC over the pregnancy and post-childbirth period. The team used temporally fine-grained measurements of HCC in the same individuals over longer-time horizons than have been examined in previous studies. Given the potential link of cortisol levels to psychiatric distress, the team also measured mothers’ psychosocial experiences. With this rich dataset in hand, the team was able to address, using a mixed-effects modeling framework, important questions concerning HCC and depressive symptom variability both within and across individuals.
Participants were recruited as part of the Brain and Behavior Infant Experiences (BABIES) project, and provided hair samples and behavioral data at three time points – during pregnancy, 3-8 weeks after childbirth, and 5-8 months after childbirth. The beauty of the HCC methodology lay in part in the ease with which samples could be collected. Without the hassle of a blood test, data collection consisted of simply cutting a hair sample from the posterior vertex of the head.
During these same visits, participants responded to questions about depressive symptoms experienced in the prior week, and about any psychosocial difficulties or stressors they experienced in the prior 6 months, such as the loss of loved ones, loss of employment, and experiences of discrimination.
After collection, each hair sample was divided into 1-cm segments, to correspond to the timescale of single months, and was sent to a collaborating lab, where an immunoassay with chemiluminescence detection measured the cortisol levels. Thus, with a single visit, the team was able to collect information on individuals’ cortisol levels from up to each of 5 months earlier.
Across participants, the study found a significant rise in mean hair cortisol (Fig. 1) over the course of pregnancy and up to childbirth – validating the ability of HCC to measure physiological rises in prepartum cortisol. In the months following childbirth, hair cortisol levels decreased, on aggregate. These changes were statistically robust when the authors created a detailed piecewise linear mixed effects model, regressing out important confounds such as the participants’ use of chemical hair treatments, their frequency of hair washing, and the distance of hair segments from the scalp.
Depressive symptoms were calculated for individuals both relative to symptom levels in the broader sample and relative to each individual’s fluctuating symptom levels over time. Notably, the study found that neither approach of calculating depressive symptoms yielded a significant relation with HCC. However, within-individual fluctuations in psychosocial adversity had a small, yet statistically significant association with HCC level. This finding provides intriguing support for the idea that mothers’ experience of psychosocial stressors might be reflected in their hair cortisol levels.
Although additional work is needed to characterize the finer time-scale dynamics of cortisol in relation to psychosocial experiences – for example, at the scale of weeks or days – this study provides a valuable view of cortisol levels in a critical period for maternal health. The ease with which measurements of hair cortisol can be obtained and scaled across large populations offers promise for its role in generating continued scientific and therapeutic insights into maternal health.
Citation: King, L. S., Humphreys, K. L., Cole, D. A., & Gotlib, I. H. (2022). Hair cortisol concentration across the peripartum period: Documenting changes and associations with depressive symptoms and recent adversity. Comprehensive Psychoneuroendocrinology, 9, 100102.
The eWEAR-TCCI awards for science writing is a project commissioned by the Wearable Electronics Initiative (eWEAR) at Stanford University and made possible by funding through eWEAR industrial affiliates program member Shanda Group and the Tianqiao and Chrissy Chen Institute (TCCI®).