European Journal of Cardiovascular Medicine

Vitamin D is a fat-soluble secosteroid hormone that plays an indispensable role in calcium and phosphate homeostasis, which is fundamental for bone mineralization and health [1]. Beyond its classical effects on the skeleton, the discovery of the Vitamin D receptor (VDR) in a wide variety of non-skeletal tissues, including muscle and nerve cells, has broadened our understanding of its pleiotropic physiological functions [2]. These include modulation of the immune system, regulation of cell proliferation, and a significant role in neuromuscular function. Consequently, Vitamin D deficiency is now implicated in a host of clinical conditions beyond rickets and osteomalacia, including autoimmune diseases, infectious diseases, and chronic pain syndromes [3].

Vitamin D deficiency has reached pandemic proportions, affecting an estimated one billion people worldwide across all ethnicities and age groups [4]. The primary source of Vitamin D for most humans is endogenous synthesis in the skin through exposure to ultraviolet B (UVB) radiation from sunlight, with dietary sources contributing to a lesser extent. Modern lifestyles, characterized by increased indoor activity, use of sunscreens, and urbanization, have severely limited adequate sun exposure, leading to widespread deficiency even in sun-replete regions [5].

A growing body of clinical evidence has linked low serum levels of 25-hydroxyvitamin D [25(OH)D], the primary circulating form and best indicator of Vitamin D status, to non-specific musculoskeletal pain (MSP) [6, 7]. The proposed mechanism is multifactorial, potentially involving the sensitization of peripheral nociceptors, as VDRs are expressed in sensory neurons [8]. Furthermore, Vitamin D deficiency can lead to a subclinical myopathy characterized by muscle weakness and diffuse aching, contributing to the symptomatology.

Medical students represent a uniquely vulnerable demographic for Vitamin D deficiency. Their rigorous academic schedule necessitates long hours of indoor study in libraries, lecture halls, and laboratories, drastically reducing their opportunity for sun exposure [9]. This is often compounded by high levels of stress and irregular dietary habits, which can further impact their nutritional status. Several studies have reported a high prevalence of Vitamin D deficiency among medical trainees [10, 11]. While the link between deficiency and MSP is established in the general population, there is a relative paucity of research that specifically investigates this clinical correlation within the medical student cohort. Understanding this association is crucial, as chronic pain can significantly impair concentration, academic performance, and overall quality of life.

Therefore, this study was designed with the primary objective of determining the prevalence of Vitamin D deficiency in a sample of undergraduate medical students. The secondary objective was to explore and quantify the association between Vitamin D status and the presence of chronic non-specific musculoskeletal pain.

Study Population and Sample Size
The study population consisted of undergraduate medical students from the first to the final year of their MBBS course. For this pilot investigation, a sample size of 80 students was recruited using a non-probability convenience sampling method from common areas of the college.

Inclusion and Exclusion Criteria
Students of either gender, aged between 18 and 24 years, who provided voluntary written informed consent were included in the study. Exclusion criteria were: (1) a known history of chronic metabolic bone diseases (e.g., Paget's disease), (2) a diagnosis of any chronic inflammatory or rheumatological condition (e.g., rheumatoid arthritis, fibromyalgia), (3) a history of specific trauma or injury related to their pain, (4) current or recent (within 6 months) use of Vitamin D or calcium supplements, and (5) pregnancy or lactation.

Data Collection Tools and Procedure
Ethical clearance was obtained from the Institutional Ethics Committee before initiating the study. Participants were briefed about the study's objectives and procedures, and confidentiality was assured.

1. Questionnaire: Each participant completed a pre-tested, structured questionnaire to gather information on:
• Sociodemographics: Age, gender, year of study.
• Lifestyle Factors: Average daily sun exposure, categorized as <30 minutes or ≥30 minutes per day.
• Musculoskeletal Pain (MSP): The presence of chronic, non-specific MSP was assessed. It was defined as a persistent or intermittent aching pain in muscles or bones, localized to at least one site (back, neck, shoulders, or limbs), lasting for more than three months, and not attributable to any specific injury.
2. Biochemical Analysis: Under aseptic conditions, a trained phlebotomist collected a 3 mL sample of venous blood from each participant into a plain vacutainer. The samples were centrifuged to separate the serum, which was then stored at -20°C until analysis. Serum levels of 25-hydroxyvitamin D [25(OH)D] were measured using a competitive chemiluminescence immunoassay (CLIA) on a fully automated analyzer (e.g., Abbott Architect i2000SR). Based on the Endocrine Society guidelines, Vitamin D status was categorized as: Deficient (<20 ng/mL), Insufficient (20–29.9 ng/mL), and Sufficient (≥30 ng/mL). For the primary analysis, participants were dichotomized into a 'Deficient' group (<20 ng/mL) and a 'Sufficient' group (≥20 ng/mL).

Statistical Analysis
Data were entered and analyzed using the Statistical Package for the Social Sciences (SPSS) version 25.0. Descriptive statistics were calculated and presented as mean ± standard deviation (SD) for continuous variables and as frequencies and percentages for categorical data. The Independent Samples t-test was used to compare the mean serum 25(OH)D levels between students with and without MSP. The Chi-square test was used to determine the association between categorical variables, primarily between Vitamin D status (Deficient/Sufficient) and the presence of MSP. A p-value of less than 0.05 was considered statistically significant.

A total of 80 medical students participated in the study. The sociodemographic and lifestyle characteristics of the participants are shown in Table 1. The mean age was 21.2 ± 1.8 years. The study included 42 males (52.5%) and 38 females (47.5%). A majority of the students (68.8%) reported having less than 30 minutes of daily sun exposure.

Table 1: Sociodemographic and Lifestyle Characteristics of Study Participants (N=80)

The prevalence of Vitamin D deficiency was alarmingly high. Based on a cut-off of <20 ng/mL, 62.5% (n=50) of the students were found to be deficient. The mean serum 25(OH)D level for the entire cohort was 18.9 ± 6.1 ng/mL. The overall prevalence of chronic non-specific musculoskeletal pain was 55.0% (n=44). As shown in Table 2, the mean serum 25(OH)D level was significantly lower in students who reported having MSP compared to their asymptomatic peers (15.2 ± 4.1 ng/mL vs. 23.5 ± 5.0 ng/mL; p<0.001).

Table 2: Comparison of Mean Serum Vitamin D Levels by Presence of Musculoskeletal Pain

Table 3 details the primary finding of the study: the association between Vitamin D status and the presence of musculoskeletal pain. A strong and highly statistically significant association was observed. Among the 50 students with Vitamin D deficiency, 40 (80.0%) reported experiencing MSP. In contrast, among the 30 students with sufficient Vitamin D levels, only 4 (13.3%) reported MSP (p<0.001). Inadequate sun exposure was also significantly associated with the presence of MSP (p=0.011).

Table 3: Association of Vitamin D Status and Sun Exposure with Musculoskeletal Pain

This study highlights two critical health issues among undergraduate medical students: an extremely high prevalence of Vitamin D deficiency and its strong clinical correlation with chronic musculoskeletal pain. The finding that 62.5% of students were Vitamin D deficient is deeply concerning, though it aligns with an increasing number of reports from similar populations in India and other parts of the world [11, 12]. This high prevalence is almost certainly multifactorial, but our data suggest that inadequate sun exposure is a major contributor, with nearly 70% of students reporting less than 30 minutes of daily sun contact. The demanding, predominantly indoor nature of medical training provides a clear explanation for this lifestyle pattern [9].

The central finding of our research is the robust association between Vitamin D deficiency and MSP. The odds of experiencing chronic pain were substantially higher in students with low Vitamin D levels. This clinical observation is consistent with a large body of literature that has established a link between hypovitaminosis D and non-specific pain syndromes [7, 13]. The biological plausibility for this connection is strong. Vitamin D is known to influence muscle cell proliferation and differentiation via the VDR, and its deficiency can result in myopathy, which manifests as muscle weakness and aches [14]. Furthermore, the discovery that Vitamin D can suppress pro-inflammatory cytokines and regulate pain pathways suggests an anti-nociceptive role, the absence of which in a deficient state could lower the pain threshold [8, 15].

The implications of these findings for the well-being and academic functioning of medical students are significant. Chronic pain is a debilitating condition that can severely affect concentration, sleep quality, and mental health, leading to a negative impact on academic performance and an overall reduced quality of life [6]. For students already navigating a high-stress environment, the added burden of physical pain can be overwhelming. As these students are the future healthcare providers, their own health and well-being are of paramount importance. The fact that this is a readily identifiable and treatable condition makes our findings particularly actionable.

This study possesses several strengths. We used a gold-standard biochemical marker [25(OH)D] to assess Vitamin D status, providing objective data to correlate with the clinical symptom of pain. We also focused on a specific, homogenous population known to be at high risk. However, certain limitations must be acknowledged. First, the study's cross-sectional design demonstrates a strong association but cannot establish causality. Second, the small sample size and use of convenience sampling may limit the generalizability of our findings to the broader medical student population. Third, both MSP and sun exposure were self-reported, which could introduce recall and subjective reporting bias. Finally, we did not assess other important confounders such as dietary calcium intake, physical activity levels, or BMI, which can also influence both Vitamin D status and musculoskeletal health.

Vitamin D deficiency is highly prevalent among medical students and is strongly associated with the presence of chronic musculoskeletal pain. This represents a significant and largely overlooked public health problem within our medical education system. There is a clear need for increased awareness among students and institutional authorities. Proactive strategies, including educational campaigns on the importance of Vitamin D, promotion of safe and adequate sun exposure, dietary counseling, and consideration for routine screening and supplementation, should be implemented to mitigate this modifiable risk factor and improve the health and well-being of future physicians.

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