Associations between serum vitamin D status and the cardiometabolic profile of patients with obstructive sleep apnea

Abstract

Purpose: Obstructive sleep apnea (OSA) and the metabolic syndrome (MetS) frequently coexist. Low serum vitamin D has been positively associated with OSA presence and severity; however, data on its link to cardiometabolic features in patients with OSA remain scarce. We aimed to assess serum 25-hydroxyvitamin D [25(OH)D] and explore its association with cardiometabolic parameters in OSA.

Methods: This was a cross-sectional study among 262 patients (49 ± 9 years old, 73% men) with polysomnography-diagnosed OSA. Participants were evaluated in terms of anthropometric indices, lifestyle habits, blood pressure, biochemical, plasma inflammatory and urinary oxidative stress markers, and the presence of MetS. Serum 25(OH)D was assessed by chemiluminescence, and vitamin D deficiency (VDD) was defined as 25(OH)D < 20 ng/mL.

Results: Median (1^st, 3^rd quartile) serum 25(OH)D levels were 17.7 (13.4, 22.9) ng/mL and 63% of participants had VDD. Serum 25(OH)D correlated negatively with body mass index (BMI), homeostasis model of assessment of insulin resistance (HOMA-IR), total cholesterol, low-density lipoprotein cholesterol, triglycerides, high-sensitivity C-reactive protein (hsCRP), and urinary oxidized guanine species (oxG), and positively with high-density lipoprotein cholesterol (all P < 0.050). In logistic regression analysis, serum 25(OH)D was associated with lower odds of MetS [odds ratio (95% confidence interval): 0.94 (0.90-0.98)], after adjustment for age, sex, season of blood sampling, Mediterranean diet score, physical activity, smoking, apnea-hypopnea index, HOMA-IR, hsCRP, and oxG. In the same multivariate model, VDD was associated with ~ twofold greater odds of MetS [2.39 (1.15, 4.97)].

Conclusion: VDD is highly prevalent and is associated with a detrimental cardiometabolic profile among patients with OSA.

Keywords: 25-Hydroxyvitamin D; Inflammation; Insulin resistance; Metabolic syndrome; Obesity; Oxidative stress; Sleep apnea; Vitamin D deficiency.

Fig. 1

Study flowchart. From November 2014 to October 2018, 357 newly diagnosed patients with obstructive sleep apnea based on an attended overnight polysomnography were prospectively referred for screening by the research team. Of the 357 patients, 59 declined to participate and 14 did not show up for the assessments. In total, 284 patients were screened for eligibility. After excluding 15 patients who did not have complete polysomnography reports, 269 provided signed written consent and were enrolled. The working sample for current analyses consisted of 262 patients with available data on serum vitamin D status

Fig. 2

a Distribution of serum 25(OH)D values in the study population. b Serum vitamin D status according to the season of blood sampling (winter: December–February; spring: March–May; summer: June–August; autumn: September–November). Results on the Y axis correspond to median serum 25(OH)D levels and the (I) bars represent interquartile ranges. Between-group differences were tested through the Kruskal–Wallis test. Abbreviations: 25(OH)D, 25-hydroxyvitamin D

Fig. 3

Scatterplots illustrating the association between serum 25(OH)D levels and a BMI, b HOMA-IR, c TG, d HDLC, e hsCRP, and f oxG. Dotted lines represent the linear regression curve (fit line) for the relationship between variables. Abbreviations: BMI, body mass index; HDLC, high-density lipoprotein cholesterol; HOMA-IR, homeostasis model of assessment of insulin resistance; hsCRP, high-sensitivity C reactive protein; oxG, oxidized guanine species; TG, triglycerides; 25(OH)D, 25-hydroxivitamin D

Fig. 4

Association between vitamin D status and the number of MetS components. Since only four patients had no MetS components, the lower two categories, i.e., 0 and 1, were combined as ≤ 1. a Results on Y axis correspond to median serum 25(OH)D levels and the (I) bars represent interquartile ranges. Between-group differences were tested through the Kruskal–Wallis test. b Results on the Y axis correspond to the prevalence (%) of vitamin D deficiency [serum 25(OH)D levels < 20 ng/mL]. Between-group differences were tested through Pearson’s chi-squared test. Abbreviations: MetS, metabolic syndrome; 25(OH)D, 25-hydroxyvitamin D