Hemoglobin Changes After Long-Term Intermittent Work at High Altitude

Abstract

Chronic high altitude hypoxia leads to an increase in red cell numbers and hemoglobin concentration. However, the effects of long-term intermittent hypoxia on hemoglobin concentration have not fully been studied. The aim of this study was to evaluate hemoglobin levels in workers commuting between an elevation of 3,800 m (2-week working shift) and lowland below 1,700 m (2 weeks of holiday). A total of 266 healthy males, aged from 20 to 69 years (mean age 45.9 ± 0.6 years), were included into this study. The duration of intermittent high altitude exposure ranged from 0 to 21 years. Any cardiac or pulmonary disorder was excluded during annual check-ups including clinical examination, clinical lab work (blood cell count, urine analysis, and biochemistry), ECG, echocardiography, and pulmonary function tests. The mean hemoglobin level in workers was 16.2 ± 0.11 g/dL. Univariate linear regression revealed an association of the hemoglobin levels with the years of exposure. Hemoglobin levels increased 0.068 g/dL [95% CI: 0.037 to 0.099, p < 0.001] for every year of intermittent high altitude exposure. Further, after adjusting for other confounding variables (age, living at low or moderate altitude, body mass index, and occupation) using multivariable regression analysis, the magnitude of hemoglobin level changes decreased, but remained statistically significant: 0.046 g/dL [95% CI: 0.005 to 0.086, p < 0.05]. Besides that, a weak linear relationship between hemoglobin levels and body mass index was revealed, which was independent of the years of exposure to high altitude (0.065 g/dL [95% CI: 0.006 to 0.124, p < 0.05]). We concluded that hemoglobin levels have a linear relationship with the exposure years spent in intermittent hypoxia and body mass index.

Keywords: body mass index; chronic intermittent hypoxia; hemoglobin; high altitude; shift workers.

FIGURE 1

Hemoglobin (Hb) levels in subjects according to their body mass index (BMI) category: normal weight (<25), overweight (25–30), and obese (≥30). ^∗P < 0.05 for differences between normal weight and obese subjects. Data presented as mean ± SEM. Statistical analysis was carried out using one-way ANOVA followed by Tukey’s multiple comparison test.

FIGURE 2

Scatter plot of correlation between the hemoglobin (Hb) levels and the years of exposure to intermittent high altitude. The best-fit line is shown, and the shaded area represents the 95% confidence intervals (n = 266).