Differences in Cardiovascular, Biochemical and Nutritional Parameters Between High- and Low-Altitude Winter Sports Athletes

<b>Background/Objectives</b>: High-altitude hypoxia may affect ECG readings, but it is unclear whether the "live-low-train-high" approach prevents these changes in winter sports athletes. <b>Methods</b>: This cross-sectional study assessed cardiovascular parameters in 102 winter-sport athletes (mean age 20 ± 4 y; 57% women), divided by training altitude into a high-altitude (HA) group (2500-3300 m, n = 70; skiers/snowboarders) and a low-altitude (LA) group (738 m, n = 32; ice hockey/figure skaters). Mid-season assessments included resting ECG, blood pressure, blood biochemistry, and three 24 h dietary recalls. <b>Results</b>: All ECG parameters were physiological, and no significant differences (<i>p</i> < 0.05) were observed in heart rate, PR interval, or QTc between groups. However, HA group exhibited higher systolic blood pressure and a short QT interval. Lactate was significantly higher in HA (<i>p</i> = 0.028). The HA diet contained more saturated fat (<i>p</i> < 0.001), cholesterol (<i>p</i> = 0.013), magnesium (<i>p</i> = 0.003) and potassium (<i>p</i> = 0.001), whereas LA athletes consumed more glucose (<i>p</i> = 0.024). In HA, total energy expenditure correlated positively (<i>p</i> ≥ 0.05) with QRS (ρ = 0.52) and QT (ρ = 0.56), while heart rate correlated inversely with vitamin D (ρ = -0.59). In LA, QTc showed strong inverse correlations with zinc (ρ = -0.62) and selenium (ρ = -0.85). <b>Conclusions</b>: This finding suggests that intermittent high-altitude training did not alter ECG patterns when nutrient intake was adequate. High lactate level and specific nutrient correlations point to a residual physiological load and a modulatory role of electrolytes, B-vitamins, and vitamin D on cardiac repolarisation.