Lifestyle behaviors and serum biochemical indicators jointly influence heat tolerance in young adult males: a cross-sectional study in Hainan region

Young adult males constitute the primary workforce in high-temperature operations, and intensified heat exposure driven by global climate change poses a severe threat to their operational efficiency and life safety. Natural individual differences exist in heat tolerance, yet systematic understanding of the influencing factors remains lacking. This study aims to systematically investigate individual difference factors affecting heat tolerance in young males through multidimensional indicators including basic physiological characteristics, lifestyle behaviors, and serum biochemical and hormonal levels, thereby providing a theoretical basis for health management and heat injury prevention of workers exposed to high-temperature environments.

A cross-sectional study was conducted among young adult males permanently residing in Hainan. A total of 160 participants were enrolled between March 25 and April 6, 2024, and based on the results of heat tolerance tests and terminal body temperature and heart rate, they were divided into a heat-intolerant group (n=35), a moderately heat-tolerant group (n=81), and a superiorly heat-tolerant group (n=44). General physiological indicators including age, height, body weight, body mass index (BMI), body surface area and body fat percentage were compared across groups. Lifestyle behaviors (smoking status, insomnia, water intake, history of heatstroke, physical fitness and adaptability to local living environment) were investigated via Wenjuanxing questionnaire. Serum biochemical indicators [aspartate aminotransferase (AST), alanine aminotransferase (ALT), urea nitrogen (UREA), creatinine (Cr), creatine kinase (CK), and creatine kinase-MB (CK-MB)] and hormones (cortisol, aldosterone, and testosterone) level were detected. Ordinal logistic regression analysis was applied to identify differential indicators influencing heat tolerance, and a confusion matrix was adopted to evaluate the prediction accuracy of the model.

Univariate analysis showed significant differences among the 3 groups in terms of BMI (P=0.017), body fat percentage (P=0.002), smoking (P=0.010), insomnia (P=0.024), history of heatstroke (P=0.019), physical fitness (P=0.002), environmental adaptability (P<0.001), Cr (P<0.001), ALT (P<0.001), cortisol (P= 0.002) and serum testosterone (P=0.002). Multivariate ordinal logistic regression analysis revealed that smoking (OR=2.958, 95%CI: 1.379 to 6.346, P=0.005), history of heatstroke (OR=3.872, 95%CI: 1.451 to 10.328, P=0.007), poor physical fitness (OR=0.047, 95%CI: 0.006 to 0.383, P=0.004), moderate environmental adaptability (OR=0.280, 95%CI: 0.107 to 0.730, P=0.009), elevated levels of Cr (OR=0.820, 95%CI: 0.762 to 0.882, P<0.001), ALT (OR=0.848, 95%CI: 0.751 to 0.957, P=0.008) and testosterone (OR=0.627, 95%CI: 0.448 to 0.875, P=0.006) were independent risk factors for decreased heat tolerance. The overall prediction accuracy of the model was 70.00%, indicating satisfactory discriminative performance.

Individual physiological and biochemical indicators (Cr, ALT and testosterone) as well as lifestyle behaviors (smoking, heatstroke history, physical fitness and environmental adaptability) are key influencing factors for heat tolerance in young adult males in Hainan region. BMI, body fat percentage, cortisol and insomnia are also significantly correlated with heat tolerance.