Association between high-altitude erythrocytosis and arterial stiffness in long-term high-altitude residents.

High-altitude erythrocytosis (HAE) may have vascular implications, but its association with arterial stiffness in long-term high-altitude residents remains unclear. We conducted a cross-sectional study of adults from Chengdu and high-altitude areas of Sichuan Province between January 2024 and February 2026. After excluding participants with ankle-brachial index <0.90 or atrial fibrillation, 3346 participants were included (2271 low-altitude and 1075 high-altitude residents). Arterial stiffness was assessed by brachial-ankle pulse wave velocity (baPWV); the primary outcome was mean baPWV, and the clinical outcome was mean baPWV ≥1800 cm/s. High-altitude residents had higher mean baPWV than low-altitude residents (1576.1 ± 403.1 vs 1474.4 ± 309.4 cm/s), with a higher prevalence of mean baPWV ≥1800 cm/s (23.8% vs 14.8%). Among high-altitude residents, 114 had HAE and 961 did not. Participants with HAE had higher mean baPWV (1969.4 ± 563.0 vs 1529.5 ± 352.0 cm/s). After adjustment for age, sex, body mass index, systolic blood pressure, heart rate, smoking, alcohol drinking, diabetes, lipid parameters and estimated glomerular filtration rate, HAE remained associated with higher mean baPWV (β, 297.5 cm/s; 95% CI, 219.6-375.5; P < 0.001) and higher odds of mean baPWV ≥1800 cm/s (OR, 3.30; 95% CI, 1.98-5.48; P < 0.001). Hemoglobin-category, continuous hemoglobin, and restricted cubic spline analyses supported a positive, nonlinear hemoglobin-baPWV association. HAE was associated with greater baPWV burden among long-term high-altitude residents, but causality cannot be inferred.