Type 2 Diabetes Mellitus (T2DM) is a prevalent metabolic disorder characterized by insulin resistance and progressive pancreatic beta-cell dysfunction, resulting in chronic hyperglycemia and associated complications (1). As the global burden of diabetes continues to rise, it remains a major contributor to increased morbidity, mortality, and healthcare utilization, especially in hospitalized patients (2). Hospitalized individuals with T2DM often experience longer lengths of stay, increased risk of infections, and higher readmission rates compared to non-diabetic counterparts (3).

Vitamin D, a fat-soluble secosteroid hormone, is increasingly recognized for its extra-skeletal effects, including modulation of the immune system, regulation of inflammatory responses, and possible influence on insulin secretion and sensitivity (4). Recent evidence has highlighted a high prevalence of vitamin D deficiency (VDD) in individuals with T2DM, which may exacerbate their vulnerability to adverse outcomes during hospitalization (5). Inadequate vitamin D levels have been linked with poor glycemic control, increased susceptibility to infections, impaired wound healing, and delayed recovery in acute care settings (6,7).

Despite the growing interest in the role of vitamin D in diabetes-related complications, few prospective cohort studies have examined the direct impact of VDD on hospitalization outcomes in T2DM patients. Understanding this association could provide a basis for early intervention and risk stratification. Therefore, this study aimed to investigate the relationship between vitamin D deficiency and clinical outcomes, including length of hospital stay, in-hospital complications, and readmission rates among hospitalized patients with T2DM.

The study population included adult patients (age ≥ 18 years) who were previously diagnosed with Type 2 Diabetes Mellitus (T2DM) and were admitted for medical management of various conditions.

Patients were enrolled consecutively based on inclusion and exclusion criteria. Those with chronic kidney disease stage 4 or higher, liver cirrhosis, malignancy, or on vitamin D supplementation in the last 3 months were excluded to eliminate potential confounding variables.

Within 24 hours of admission, venous blood samples were collected to assess serum 25-hydroxyvitamin D [25(OH)D] levels using chemiluminescence immunoassay. Patients were divided into two groups: Vitamin D deficient (<20 ng/mL) and non-deficient (≥20 ng/mL), based on Endocrine Society clinical practice guidelines.

Data on demographic variables, glycemic control (HbA1c), duration of diabetes, and comorbidities were recorded. Hospitalization outcomes assessed included length of hospital stay (LOS), development of in-hospital complications such as infections, acute kidney injury, and cardiovascular events, and 30-day readmission rate. All outcomes were tracked using hospital records and patient follow-up.

Statistical analysis was performed using SPSS software version 26. Descriptive statistics were expressed as means ± standard deviations or percentages, as appropriate. Independent t-tests and Chi-square tests were used for between-group comparisons. Logistic regression analysis was conducted to evaluate the association between vitamin D status and clinical outcomes, adjusting for potential confounders. A p-value less than 0.05 was considered statistically significant.

A total of 200 patients with Type 2 Diabetes Mellitus were included in the study. Out of these, 118 patients (59%) were found to be vitamin D deficient (<20 ng/mL), while 82 patients (41%) had sufficient levels (≥20 ng/mL). The baseline demographic and clinical characteristics of both groups are summarized in Table 1.

Patients in the vitamin D deficient group had a higher mean age (58.6 ± 9.4 years) compared to the non-deficient group (56.2 ± 10.1 years). The mean HbA1c level was also higher in the deficient group (8.7 ± 1.2%) than in the non-deficient group (7.9 ± 1.0%; p = 0.02). Hypertension and cardiovascular disease were more prevalent in the vitamin D deficient group, though the difference was not statistically significant (Table 1).

Table 1: Baseline Characteristics of the Study Population

Analysis of hospitalization outcomes showed that the average length of hospital stay (LOS) was significantly longer in the vitamin D deficient group (8.2 ± 3.1 days) compared to the non-deficient group (5.4 ± 2.6 days; p < 0.001). The incidence of in-hospital complications, including infections and acute kidney injury (AKI), was also higher in the deficient group. Additionally, the 30-day readmission rate was elevated among vitamin D deficient patients (Table 2).

Table 2: Hospitalization Outcomes in Both Groups

Multivariate regression analysis identified vitamin D deficiency as an independent predictor of prolonged hospital stay (adjusted OR = 2.5, 95% CI: 1.3–4.8, p = 0.006) and in-hospital complications (adjusted OR = 1.9, 95% CI: 1.1–3.5, p = 0.021).

As shown in Table 2, vitamin D deficiency was consistently associated with poorer hospitalization metrics, suggesting a potential role for early screening and correction in patients admitted with T2DM.

The present study demonstrated a significant association between vitamin D deficiency and adverse hospitalization outcomes among patients with Type 2 Diabetes Mellitus (T2DM). Specifically, vitamin D-deficient individuals had prolonged hospital stays, a higher incidence of in-hospital complications such as infections and acute kidney injury (AKI), and increased 30-day readmission rates compared to those with sufficient vitamin D levels. These findings support emerging evidence that vitamin D plays a multifaceted role beyond bone health, particularly in glycemic regulation, immune function, and inflammation control (1,2).

Several mechanisms could explain the observed association between low serum 25(OH)D levels and worsened hospitalization outcomes. Vitamin D modulates the innate and adaptive immune systems by enhancing macrophage function and suppressing pro-inflammatory cytokines, which may reduce susceptibility to infections in hospitalized patients (3,4). Moreover, vitamin D receptors (VDRs) are expressed in pancreatic β-cells and various peripheral tissues, suggesting a role in insulin secretion and sensitivity (5). Studies have shown that vitamin D supplementation may improve insulin resistance and glycemic control, potentially stabilizing the metabolic state during hospitalization (6,7).

Our findings are consistent with previous investigations that reported a high prevalence of vitamin D deficiency among diabetic individuals, especially those requiring inpatient care (8,9). A study by Tishkoff et al. observed that low vitamin D status in hospitalized patients with diabetes correlated with increased healthcare utilization, including longer hospital stays and a greater likelihood of ICU admission (10). Another study by Boucher et al. highlighted the pro-inflammatory environment created by vitamin D deficiency, which may exacerbate diabetic complications and hinder recovery from acute illnesses (11).

In the current study, the length of stay was significantly longer in vitamin D-deficient patients. This aligns with observations by Lee et al., who reported that inadequate vitamin D status was independently associated with delayed recovery in medical inpatients, particularly in those with comorbidities such as diabetes and cardiovascular disease (12). Furthermore, infections were notably more frequent in the vitamin D-deficient group. This is supported by Martineau et al., who demonstrated in a meta-analysis that vitamin D supplementation reduced the risk of acute respiratory infections, particularly in deficient individuals (13).

Acute kidney injury (AKI), a common complication in diabetic inpatients, was also more prevalent in the vitamin D-deficient group in our study. Previous research has suggested that vitamin D may offer renal protection through anti-inflammatory and anti-fibrotic pathways (14). The higher rate of 30-day readmission in deficient patients could reflect unresolved inflammation, poor metabolic control, or complications that persisted after discharge, as indicated by similar findings in the literature (15).

Despite the compelling findings, this study has certain limitations. Being a single-center study may limit the generalizability of the results. Moreover, confounding factors such as nutritional status, sun exposure, and seasonal variation in vitamin D levels were not fully controlled. Longitudinal studies with intervention arms involving vitamin D supplementation are required to establish causality and evaluate potential benefits on clinical outcomes.

This study highlights a significant association between vitamin D deficiency and adverse hospitalization outcomes in patients with Type 2 Diabetes Mellitus. Vitamin D-deficient individuals experienced longer hospital stays, higher rates of complications, and increased 30-day readmissions. These findings suggest that early identification and correction of vitamin D deficiency may contribute to improved clinical outcomes and reduced healthcare burden in this high-risk population.

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