Effects of Altitude on Thyroid Disorders according to Chinese Three-Rung, Ladder-like Topography：National Cross- Sectional Study

Abstract

Abstract Background: Chinese topography appears a three-rung ladder-like distribution of decreasing elevation from northwest to southeast, which is divided by two sloping edges. To explore the association between three-rung ladder-like regions and thyroid disorders according to unique Chinese topographic features, we conducted an epidemiological cross-sectional study from 2015–2017 that covered all 31 mainland Chinese provinces. Methods: A total of 78,470 participants aged ≥18 years from a nationally representative cross-sectional study were included. Serum thyroid peroxidase antibody, thyroglobulin antibody, and thyroid-stimulating hormone levels; urine iodine concentration; and thyroid volume were measured. The three-rung ladder-like distribution of decreasing elevation from northwest to southeast in China was categorized into three topographic groups according to elevation: first ladder, >3000 m above sea level; second ladder, descending from 3000 - 500 m; and third ladder, descending from 500 m to sea level. The third ladder was further divided into groups A (500-100 m) and B (<100 m). Associations between geographic factors and thyroid disorders were assessed using linear and binary logistic regression analyses. Results: Participants in the first ladder group were associated with lower thyroid peroxidase (β=-4.69; P=0.00) , thyroglobulin antibody levels (β=-11.08; P=0.01), and the largest thyroid volume (β=1.74; P=0.00), compared with the other groups. The second ladder group was associated with autoimmune thyroiditis (odds ratio=1.30, 95% confidence interval [1.18-1.43]) and subclinical hypothyroidism (odds ratio=0.61, 95%confidence interval [0.57-0.66]) (P<0.05) compared with the first ladder group. Group A (third ladder) (500-100 m) was associated with thyroid nodules and subclinical hypothyroidism (P<0.05). Furthermore, group B (<100 m) was positively associated with autoimmune thyroiditis, thyroid peroxidase and thyroglobulin antibody positivity, and negatively associated with overt hypothyroidism, subclinical hypothyroidism, and goiter compared with the first ladder group(P<0.05). Conclusion: We are the first to investigate the association between different ladder regions and thyroid disorders according to unique Chinese topographic features. The prevalence of thyroid disorders varied among the three-rung ladder-like topography groups in China, with the exception of overt hyperthyroidism.