Abstract: Objective To investigate the prevalence of vitamin D deficiency and its association with blood eosinophil count in healthy population and patients with chronic obstructive pulmonary disease (COPD). Methods We analyzed the data of a total 6163 healthy individuals undergoing routine physical examination in our hospital between October, 2017 and December, 2021, who were divided according to their serum 25(OH)D level into severe vitamin D deficiency group (<10 ng/mL), deficiency group (<20 ng/mL), insufficient group (<30 ng/mL) and normal group (≥30 ng/mL). We also retrospectively collected the data of 67 COPD patients admitted in our department from April and June, 2021, with 67 healthy individuals undergoing physical examination in the same period as the control group. Routine blood test results, body mass index (BMI) and other parameters were obtained from all the subjects, and logistic regression models were used to investigate the association between 25(OH)D levels and eosinophil count. Results The overall abnormal rate of 25(OH)D level (<30 ng/mL) in the healthy individuals was 85.31%, and the rate was significantly higher in women (89.29%) than in men. Serum 25(OH)D levels in June, July, and August were significantly higher than those in December, January, and February. In the healthy individuals, blood eosinophil counts were the lowest in severe 25(OH)D deficiency group, followed by the deficiency group and insufficient group, and were the highest in the normal group (P<0.05). Multivariable regression analysis showed that an older age, a higher BMI, and elevated vitamin D levels were all risk factors for elevated blood eosinophils in the healthy individuals. The patients with COPD had lower serum 25(OH)D levels than the healthy individuals (19.66±7.87 vs 26.39±9.28 ng/mL) and a significantly higher abnormal rate of serum 25(OH)D (91% vs 71%; P<0.05). A reduced serum 25(OH)D level was a risk factor for COPD. Blood eosinophils, sex and BMI were not significantly correlated with serum 25(OH)D level in patients with COPD. Conclusion Vitamin D deficiency is common in both healthy individuals and COPD patients, and the correlations of vitamin D level with sex, BMI and blood eosinophils differ obviously between healthy individuals and COPD patients.

Key words: serum vitamin D; healthy population; serum 25(OH) D; chronic obstructive pulmonary disease; blood eosinophils