Sex-Specific Patterns of Cortisol Fluctuation, Stress, and Academic Success in Quarantined Foreign Medical Students During the COVID-19 Lockdown.

Cortisol is built into the circadian clock mechanism, but it is also the body's natural response to stress. Insight into sex-specific cortisol fluctuations may elucidate individual differences in physiological and pathological patterns. This cross-sectional study examined sex-specific adaptation to stress induced by COVID-19 pandemic and lockdown in foreign medical students at I. Horbachevsky Ternopil National Medical University, Ukraine (TNMU). Salivary cortisol was analyzed using cluster-based mathematical modeling to identify natural groupings in the data. Perceived stress was measured using Perceived stress scale-10 (PSS-10). The academic success was accessed from the official records of the TNMU. Average value of area under the curve (AUC) of daily salivary cortisol from the whole sample showed that men had higher cortisol than women. Mathematical clustering explained shift of the cortisol peak, and divided sample into 5 clusters-two of which had predicted daily cortisol pattern and represented most participants (65.6% men and 73.6% women), while the rest had aberrant daily cortisol pattern. Females had higher total PSS-10 score than males. PSS-10 subscales correlated with aberrant daily cortisol pattern. Unexpectedly, COVID-related circumstances did not have impact on participants' academic success.