Prediction of academic outcomes by serum cortisol, perceived academic stress, perceived memory performance, and physical activity among preclinical undergraduate medical students: a short-term observational study

Stress is common among medical students and adversely affects memory function and academic performance. Cortisol and physical activity (PA) are important physiological and lifestyle factors, yet evidence on their combined effects in military medical students is limited. This study examined whether serum cortisol, perceived stress, perceived memory performance, and PA predict academic outcomes among preclinical students in a military-based institution. A short-term prospective observational study was conducted among Years 1–2 preclinical medical students at Universiti Pertahanan Nasional Malaysia from January to September 2025, five weeks before the end-of-semester I examination (n = 106). Baseline assessments included perceived stress (Medical Student Stressor Questionnaire, MSSQ), perceived memory performance (Prospective-Retrospective Memory Questionnaire, PRMQ), and PA levels (Short-Form International Physical Activity Questionnaire, IPAQ-SF), and morning serum cortisol concentration. Participants were stratified into risk groups and sub-groups based on combinations of perceived stress, serum cortisol tertiles, and PA levels (expressed as metabolic equivalent of task, MET) and were followed across two semesters. Academic outcomes included grade point average (GPA) and the requirement for repeat semesters. The participants’ median age was 20 years (interquartile range: 19.6–20.7) with approximately 1.5:1.0 female-to-male ratio. Perceived stress correlated positively with perceived memory problems (r = 0.445, p < 0.001), while serum cortisol showed no continuous correlation with the other study variables. On ordinal scales, the “high stress + high cortisol” was associated with poorer perceived memory performance (p = 0.034), whereas “low stress + high PA” was associated with better perceived memory performance (p = 0.027). High-risk students exhibited significantly increased risks of attaining lower GPA in semester I and semester II, with relative risks of 3.10 and 2.54, respectively (p < 0.01). Although PA moderated these associations, it did not eliminate the elevated academic risk. Compared with the “low risk + high MET” group, both “high risk + high MET” (RR = 3.33 and 3.87, respectively, p < 0.01) and “high risk + low MET” (RR = 3.24 and 3.91, respectively, p < 0.05) showed further increased risks of lower GPA in both semesters. Risk stratifications did not predict repeat semester requirements. Higher perceived stress combined with higher cortisol was associated with poorer perceived memory and increased risk of lower academic performance across two semesters. These effects were partially mitigated by PA. The study findings support the implementation of integrated stress-management strategies and structured PA programmes to enhance cognitive function and academic performance among medical students in military institutions.