European Journal of Cardiovascular Medicine

Obstructive Sleep Apnoea (OSA) is a prevalent and potentially serious sleep disorder characterized by repetitive episodes of upper airway obstruction during sleep, resulting in intermittent hypoxia, sleep fragmentation, and heightened sympathetic nervous system activity [1]. These pathophysiological disturbances are associated with a spectrum of adverse outcomes, including excessive daytime sleepiness, impaired cognitive performance, cardiovascular complications, and increased all-cause mortality. According to standard diagnostic criteria, OSA in adults is confirmed via overnight polysomnography or home sleep apnea testing (HSAT), which reveals either (1) five or more predominantly obstructive respiratory events (obstructive and/or mixed apneas, hypopneas, or respiratory effort–related arousals [RERAs]) per hour of sleep in association with clinical symptoms or comorbidities, or (2) fifteen or more such events per hour irrespective of clinical context [2].

Epidemiological data from India estimate the prevalence of OSA and Obstructive Sleep Apnoea–Hypopnoea Syndrome (OSAHS) at 13.74% and 3.6%, respectively, with higher rates reported in males (4.9%) compared to females (2.1%) [3]. Concurrently, vitamin D deficiency (VDD) has emerged as a widespread public health concern. Serum 25-hydroxyvitamin D [25(OH)D] levels ≥30 ng/mL are considered sufficient, whereas levels between 21–29 ng/mL represent relative insufficiency [4].

Vitamin D, although classically recognized for its pivotal role in calcium and phosphate metabolism and bone homeostasis, exerts numerous pleiotropic effects due to the widespread distribution of vitamin D receptors (VDRs) across various tissues. Notably, VDRs are expressed in the brainstem and hypothalamus—regions integral to sleep regulation—suggesting a potential neuromodulatory role in sleep physiology [6]. Vitamin D also plays a role in immune modulation and insulin sensitivity, and its deficiency has been linked to chronic inflammation and metabolic dysregulation—both of which are implicated in the pathogenesis of OSAHS [5]. Furthermore, VDD has been hypothesized to contribute to pharyngeal dilator muscle dysfunction, thereby exacerbating upper airway collapsibility, a core feature of OSAHS [6]. Given these multifactorial biological interactions, the current study aims to assess the correlation between serum 25(OH)D levels and the severity of OSAHS in the Indian population

This cross-sectional observational study was conducted at Jain ENT Hospital, Jaipur, over a period of six months, from May to October 2023. The study aimed to assess the correlation between serum 25-hydroxyvitamin D [25(OH)D] levels and the severity of Obstructive Sleep Apnoea–Hypopnoea Syndrome (OSAHS) in adult patients. A total of 100 adult patients newly diagnosed with OSAHS were enrolled in the study. Participants were recruited from the outpatient and inpatient departments of the hospital. Informed consent was obtained from all participants prior to inclusion in the study.

Inclusion Criteria

• Adults aged over 20 years
• Patients recently diagnosed with OSAHS via overnight polysomnography

Exclusion Criteria

• Patients unwilling to provide consent
• Patients currently on vitamin D or calcium supplementation
•  

Study Procedure

All enrolled patients underwent overnight polysomnography, and OSAHS severity was graded as mild, moderate, or severe based on the Apnoea–Hypopnoea Index (AHI) in accordance with the American Academy of Sleep Medicine (AASM) 2012 guidelines. Blood samples were collected for measuring serum 25(OH) vitamin D levels. Vitamin D status was categorized as deficient (<20 ng/mL), insufficient (21–29 ng/mL), or sufficient (≥30 ng/mL). The distribution of vitamin D levels was then compared across different OSAHS severity categories.

Statistical Analysis

All data were compiled and entered into Microsoft Excel and analyzed using the Statistical Package for Social Sciences (SPSS) version 21.0 (IBM Corp., Chicago, IL, USA). Descriptive statistics were used to summarize demographic and clinical variables. The Chi-square test was employed to examine associations between categorical variables, including obesity class and OSAHS severity in relation to vitamin D levels. A p-value of <0.05 was considered statistically significant

A total of 100 patients diagnosed with obstructive sleep apnoea–hypopnoea syndrome (OSAHS) were included in the study. The demographic distribution revealed that the majority of participants were aged between 40 and 59 years. Specifically, 30% were in the 40–49-year age group, and 36% belonged to the 50–59-year group. Only 2% each were from the youngest (20–29 years) and oldest (70–79 years) age groups, while 14% and 16% fell in the 30–39 and 60–69-year brackets, respectively. Gender distribution showed a male predominance, with 62% of participants being male and 38% female, indicating a male-to-female ratio of approximately 1.6:1. [Table 1]

Table 1: Demographic Distribution of Participants by Age and Gender (n = 100)

The relationship between obesity classification and vitamin D status was examined (Table 2). Among the participants, 3% were overweight, 21% were classified under Obesity Class I, and 76% fell into Obesity Class II. Vitamin D deficiency (<20 ng/mL) was observed in 41% of the total sample, insufficiency (21–29 ng/mL) in 24%, and sufficiency (≥30 ng/mL) in 35%. The majority of vitamin D–deficient individuals were found in Obesity Class II. However, statistical analysis using the chi-square test demonstrated no significant association between obesity class and vitamin D levels (χ² = 1.4884; p = 0.828).

Table 3: Correlation between Obesity Class and Vitamin D

Similarly, the correlation between OSAHS severity and vitamin D status was analyzed (Table 3). Among the 100 participants, 17% were classified with mild OSAHS, 20% with moderate, and 63% with severe OSAHS. Vitamin D deficiency was most prevalent among individuals with severe OSAHS (27%), followed by those with mild (7%) and moderate (6%) disease severity. Despite this trend, the association between OSAHS severity and vitamin D levels was not statistically significant (χ² = 1.854; p = 0.762).

Overall, the results indicate that neither obesity class nor severity of OSAHS was significantly associated with serum 25(OH) vitamin D levels in the studied population.

Table 3: Correlation between OSA Severity & Vitamin D

Obstructive Sleep Apnoea (OSA) has emerged as a significant global health concern, affecting a substantial proportion of the adult population. Its impact is far-reaching, ranging from excessive daytime somnolence and reduced quality of life to an increased risk of occupational hazards and road traffic accidents [7]. Moreover, OSA is now recognized as an independent risk factor for cardiovascular morbidity and mortality due to its association with sympathetic overactivity, oxidative stress, and systemic inflammation [8].

The present cross-sectional study aimed to explore the relationship between serum 25-hydroxyvitamin D [25(OH)D] levels and the severity of OSAHS among Indian adults. Although earlier hypotheses proposed a potential pathophysiological link between vitamin D deficiency (VDD) and OSA through mechanisms such as impaired neuromuscular function, systemic inflammation, and central dysregulation of sleep, our findings did not demonstrate a statistically significant association between serum vitamin D levels and OSA severity.

This result is in concordance with several previous studies. For instance, Mete et al. (2013) reported lower 25(OH)D levels in OSA patients compared to controls but did not find a significant difference in mean levels between groups [9]. Similarly, Banu Salepci et al. (2017) found no significant correlation between serum 25(OH)D levels and AHI severity [11]. Ahmet Cemal Pazarli et al. (2019) also reported lower vitamin D levels in patients with both OSA and obesity hypoventilation syndrome (OHS), yet failed to demonstrate a direct association between OSA and bone mineral density (BMD) or vitamin D status [13]. Furthermore, de Oliveira DL et al. (2021), in the EPISONO cohort, identified short sleep duration—but not AHI—as an independent factor associated with reduced vitamin D levels, highlighting the complexity of sleep–vitamin D interactions, particularly in males [15].

Conversely, some studies have found an inverse relationship between serum vitamin D levels and OSA severity. Kerley et al. (2016) reported a significant negative correlation between 25(OH)D and AHI in Caucasian adults with OSAHS, suggesting a potential protective role of vitamin D in sleep-disordered breathing [10]. Cindy Lee P. Neighbors et al. (2018), in a systematic review and meta-analysis, noted relatively insufficient vitamin D levels in OSA patients compared to controls, albeit with heterogeneity among the included studies [12]. A more recent meta-analysis by Xiaoyan Li et al. (2020) supported this notion by suggesting a possible correlation between low serum vitamin D and OSA, though it acknowledged that the strength of evidence was modest and possibly confounded by other metabolic factors [14]. Additionally, a study by Kagan Tur et al. (2022) demonstrated an independent association between 25(OH)D levels and OSA severity in patients living at high altitudes, further indicating that geographic and environmental factors may influence this relationship [16].

Of particular relevance is the 2023 study by Michael Georgoulis et al., which emphasized that vitamin D deficiency was highly prevalent in newly diagnosed OSA patients and was significantly associated with an unfavorable cardiometabolic profile [17]. This raises the possibility that while VDD may not directly impact AHI-based OSA severity, it could still contribute to the broader comorbidity spectrum in OSA patients.

Given these varied findings, it is plausible that the relationship between vitamin D and OSA is multifactorial and influenced by additional variables such as body mass index (BMI), sunlight exposure, geographic latitude, comorbidities, and genetic predisposition. The lack of significant correlation in our study may also be attributed to its cross-sectional design, limited sample size, and absence of longitudinal follow-up.

Table 4: Comparison of the Present Study with Previous Studies on Vitamin D and OSA

The present study concluded that there was no statistically significant association between serum 25(OH) vitamin D levels and the severity of Obstructive Sleep Apnoea–Hypopnoea Syndrome (OSAHS) in the Indian population. While vitamin D deficiency was prevalent among participants, it did not correlate with increasing OSAHS severity. These findings suggest that vitamin D may not independently contribute to the pathogenesis of OSAHS. However, the study’s cross-sectional design and limited sample size may have restricted the ability to detect subtle associations. Larger, multi-centric, and longitudinal studies are recommended to further explore this potential relationship and clarify underlying mechanisms

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