Vitamin D deficiency in high-altitude populations: 25(OH)D level and association with systemic inflammation

This study aims to investigate the prevalence of serum vitamin D deficiency in the Xining, Qinghai Province (elevation 2260 m, oxygen partial pressure 16.10 kPa, 36°13'-37°28'N) and to explore the correlation between 25-hydroxyvitamin D [25(OH)D] levels and inflammatory markers.

A total of 2,080 subjects were enrolled, serum 25(OH)D, and inflammatory markers-including procalcitonin (PCT), interleukin 6 (IL-6), and C reactive protein (CRP) -were measured. According to serum 25(OH)D concentrations, participants were divided into three groups: vitamin D sufficiency (> 30 ng/mL), insufficiency (20-30 ng/mL), and deficiency (< 20 ng/mL). Spearman correlation analysis, partial correlation analysis and Logistic regression analysis were performed.

The mean 25(OH)D concentration was 13.99 ± 7.20 ng/mL, with the proportions of vitamin D deficiency, insufficiency and sufficiency being 83.65%, 13.65% and 2.70%, respectively. The levels of PCT, IL-6 and CRP in the deficiency group were significantly higher than those in the other two groups (P < 0.05). The vitamin D deficiency was higher in females than in males (87.95% vs. 77.47%, P < 0.05). The 25(OH)D level peaked in summer and reached the lowest level in winter (P < 0.05), while no significant intergroup difference was observed across different age groups. PCT, IL-6 and CRP were significantly negatively correlated with 25(OH)D (r=-0.674, -0.533, -0.292, P < 0.01), and these correlations remained significant after adjustment for confounding factors (P < 0.01). Logistic regression analysis revealed that female gender (OR = 4.043), PCT (OR = 2491.808), IL-6 (OR = 1.903) and CRP (OR = 1.608) were independent risk factors for vitamin D deficiency (P < 0.01).

Residents in high-altitude Xining suffer from severe vitamin D deficiency correlated with heightened inflammation. Female sex and elevated inflammatory biomarkers independently increase deficiency risk, and seasonal sunlight regulates 25(OH)D levels. Gender- and season-specific vitamin D supplementation could mitigate inflammatory load in highland residents.