Hair cortisol as a biomarker of stress and resilience in South African mixed ancestry females.

BACKGROUND: Hair cortisol concentrations (HCC) are increasingly used as a biomarker of stress, however limited research exists regarding the relationship between HCC and protective factors, such as resilience. Additionally, studies measuring HCC need to account for possible confounders, and these factors have not been examined in sufficiently diverse settings. OBJECTIVES: Our objectives were to identify determinants of HCC in a sample of mixed ancestry adults and investigate the association of HCC with measures of self-perceived stress and resilience. METHODS: Our sample comprised 164 females (mean age 46.5 years, SD = 15.0), self-identifying as mixed ancestry, who were control participants in a case-control study (SHARED ROOTS), conducted in Cape Town, South Africa from May 2014 until June 2017. We examined which socio-demographic, hair related, clinical and behavioural factors were associated with HCC in both unadjusted and adjusted linear regression models. Furthermore, the relationship of HCC with self-perceived stress and resilience scores were also examined. RESULTS: HCC (Mdn 4.4 pg/ml; IQR 2.8; 11.4) were significantly positively associated with hair product use and breastfeeding, and significantly negatively associated with age, level of education, duration of sun exposure, duration of storage, and demonstrated a trend towards significance with frequency of hair washing, in adjusted models. HCC were inversely associated with CD-RISC scores (adj ß = -0.179, p =  0.012) but were not significantly associated with PSS scores (adj ß = -0.001, p =  0.989). CONCLUSIONS: We identified specific determinants of HCC in our sample, including the first indication that sun exposure has an effect on HCC under naturalistic conditions. These potential confounders need to be controlled for in the design and analysis of future studies. HCC may be a biomarker of resilience to stress, rather than perceived stress. Further research measuring HCC in more diverse settings and populations and including constructs related to resilience are needed.