Vitamin D levels, general health status, and work productivity among healthcare workers—a scoping review of published literature (2010–2025)

Abstract

Introduction:

The risk for Vitamin D deficiency has been reported to be elevated among healthcare workers (HCWs), a fact that raises concerns about their health, resilience, and work performance. The objective of the study is to review published literature on Vitamin D deficiency among HCWs, reported health implications as well as the association with productivity.

Methods:

A comprehensive search of two databases (2010–2025), PubMed and Scopus was conducted with Google Scholar used as a supplementary source following PRISMA-ScR guidelines. The inclusion criteria were full-text studies in English enrolling HCWs per WHO definition, measuring serum 25(OH)D, and reporting health or work-related outcomes.

Results:

Thirty-six studies met the criteria 30 cross-sectional, 2 prospective, 4 interventional studies, 2 of which were Randomized Controlled Trials (RCTs). Vitamin D deficiency was highly prevalent across studies with reported prevalence ranging from 30% to over 90% varying by geographic region, season, professional role, deficiency threshold and assay method, particularly among nurses and shift workers. Key determinants included indoor work, long shifts, night duties, limited sun exposure, female sex, younger age, higher Body Mass Index (BMI), veiling, and lack of supplementation. Seasonal variation was confirmed. Deficiency was linked to immune vulnerability (higher SARS-CoV-2 infection), musculoskeletal issues, and mixed evidence for mental health outcomes. Limited data suggest higher Vitamin D levels may reduce presenteeism. RCTs demonstrated that high-dose supplementation improved serum levels and reduced respiratory infections.

Conclusion:

Existing literature points that Vitamin D inadequacy among HCWs represents significant occupational health concern highlighting important evidence gaps and future research priorities.

1 Introduction

Healthcare workers (HCWs) constitute the backbone of all functioning health systems, worldwide. However, they often face unique challenges in the occupational setting that can compromise their physical health, mental wellbeing and their work performance (1–4). Long working hours, shift work, limited sun exposure, irregular work schedule, and high stress levels are common in healthcare settings and may contribute to a broad range of health issues, including Vitamin D deficiency (5). Vitamin D, a fat-soluble prohormone, primarily synthesized through skin exposure to solar Ultraviolet B (UVB) radiation. It plays a crucial role not only in musculoskeletal health but also in immune function, mood regulation, cardiovascular function and overall metabolic health (6–8).

Emerging evidence suggests that Vitamin D deficiency is highly prevalent among healthcare professionals, particularly those working indoors or on rotating shifts (5). Studies have shown that physicians, medical residents, nurses, and healthcare students often exhibit lower serum 25-hydroxyVitamin D [25(OH)D] levels compared to the general population, due to reduced sunlight exposure and irregular work schedules (5).

Given the ongoing debate regarding optimal serum concentrations of 25-hydroxyVitamin D, the definitions of Vitamin D deficiency, insufficiency, and sufficiency remain approximate. Multiple health authorities have converged on similar Vitamin D serum levels classifications, with slight variations in precise thresholds (9–11). National Academy of Medicine (formerly Institute of Medicine) currently defines deficiency as serum 25(OH)D levels below 12 ng/mL, insufficiency when levels are between 12 and 20 ng/mL, while sufficiency is considered when levels exceed 20 ng/mL (12). However, levels exceeding 70 ng/mL (125 nmol/L) are considered potentially toxic (13, 14) as they have been associated with adverse health outcomes, primarily due to hypercalcemia (10).

There is increasing interest in the link between micronutrient status and occupational performance (15–17). Low Vitamin D levels have been associated with fatigue, musculoskeletal pain, depressive symptoms, and diminished work efficiency (18). Among healthcare workers, these effects may translate into reduced productivity, higher absenteeism, and compromised patient care quality. Both presenteeism—where employees are physically present but unable to perform at full capacity due to health issues—and sickness absenteeism contribute to productivity losses (19). Presenteeism is typically quantified in occupational health research, using validated tools, including the Stanford Presenteeism Scale (SPS) and the Work Productivity and Activity Impairment (WPAI) questionnaire. Furthermore, given the role of calciferol in mental health and its deficiency being linked to neurodegenerative conditions and impaired cognitive function, low Vitamin D may indirectly exacerbate declines in work performance (20).

Despite a growing body of research, the precise nature of the relationship between Vitamin D status, general health, and productivity among healthcare workers remains unclear. Therefore, conducting a literature review is useful to map existing evidence, identify key concepts, and highlight knowledge gaps. This review aims to examine the association between Vitamin D levels, health outcomes, and occupational productivity among healthcare workers, with the goal of informing future research, guiding workplace wellness initiatives, and strengthening occupational health policies.

2 Methods

2.1 Protocol

This scoping review was conducted according to PRISMA- ScR guidelines (21). A formal review protocol was not preregistered in PROSPERO or OSF, as protocol registration is not consistently required for scoping reviews and PROSPERO does not universally accept scoping review protocols. Nevertheless, we used the PCC framework aligned with PICO (P- population, patient, problem, I- intervention, C- comparison, O-outcome) logic to formulate the research question which is suitable for scoping reviews: Population (P) healthcare workers (nurses, physicians, medical residents, healthcare students and allied professionals) and anyone included by WHO definition (22). Concept (C) Vitamin D levels, measured as serum 25-hydroxyVitamin D concentration, 25(OH)D deficiency and its documented or potential impact on physical health, mental health and work- related productivity outcomes (absenteeism, presenteeism, performance indicators), Context (C):in healthcare settings of any geographical region, country, climate and socioeconomic status.

2.2 Eligibility criteria and search criteria

To be included in this review the article could be a published study of any study design (observational, interventional, cross- sectional) that reported on healthcare workers as the primary population, measured Vitamin D status using serum 25(OH)D concentration, assessed outcomes related to general health status (e.g., fatigue, immune function, musculoskeletal health, mental health or work- related outcomes; e.g., productivity, absenteeism, presenteeism, job performance, cognitive or physical performance). The exclusion criteria were all studies without primary data, animal studies and abstract - only publications, systematic reviews and narrative reviews, population- based studies not specifically involving healthcare workers. However, secondary analyses and reviews were screened for backward citation- searching when necessary to ensure that no primary studies were missed. A meticulous search has been conducted in the following two databases: PubMed, Scopus from 1 January 2010 until 31 December 2025. Google Scholar was used exclusively as a supplementary search tool to enhance the sensitivity of the review by identifying potentially relevant studies not indexed in traditional bibliographic databases. Records were screened sequentially by relevance until retrieval saturation was reached. Accordingly, primary evidence identification and all PRISMA reporting were based solely on structured searches conducted in PubMed and Scopus.

Additional sources included reference lists of the included articles. Search strings combined PCC elements using Boolean operators were used to capture the relevant studies Supplementary material 1. The study selection process is presented in a PRISMA flow diagram (Figure 1).

Figure 1

All the retrieved files were imported to the reference manager (Clarivate Endnote 2025.2, Bld 19,737), duplicates were removed and two reviewers, P. N and the author E. V., independently screened title and abstracts. Any discrepancies were resolved through discussion. Data was extracted from the included studies, using a standardized charting form, capturing the following information: Author/ Year /Location/Population/Study Design/ Sample Size /Vitamin D Measurements/Outcomes Health /Productivity/Key Findings- Supplementary Tables 1–3 (Comprehensive List of the included studies). Vitamin D concentrations were standardized and reported in ng/mL across all included studies. When values were originally reported in nmol/L, systematic conversion was applied using the standard factor (1 ng/mL = 2.496 nmol/L). Original study-specific deficiency thresholds were retained and are summarized in Table 1.

The studies have been then categorized in four thematic areas: (1) Prevalence of Vitamin D deficiency or insufficiency and associated risk factors among HCWs. (2) Health implications of Vitamin D deficiency on healthcare workers. (3) Association of Vitamin D inadequacy with work productivity. (4) The role of supplementation in addressing Vitamin D deficiency among healthcare workers.

3 Results

The search yielded a total of 36 publications that met the inclusion criteria and were further investigated (Figure 1). The studies were conducted between 2010 and 2025, comprising of 30 cross-sectional studies (CSSs) (Table 2), 4 interventional studies (INSs) (Table 3), two of them being Randomized Controlled Trials (RCTs) and 2 longitudinal prospective studies (Table 4).

A notable surge during the COVID- 19 pandemic with a clear trend consisting of pre-pandemic studies (2010–2019) mainly examined general prevalence of Vitamin D deficiency, associations with bone health, cardiometabolic risks and occupational factors like shift work and seasonal variation. Pandemic- era studies (2020 onward) show a marked increase in research on Vitamin D and immune function (COVID- 19 susceptibility, severity and seroconversion), supplementation trials aimed at preventing COVID-19 or reducing morbidity, occupational vulnerability during lockdowns and reduced sun exposure and a broader interest in Vitamin D as modifiable risk factor for infection and presenteeism. Across the board, the included studies consistently highlighted a high prevalence of Vitamin D deficiency among healthcare workers. Many also identified specific occupational risk factors contributing to this deficiency. To enhance clarity and support a comprehensive understanding of the findings, the results were systematically organized into four overarching semantic themes.

3.1 Prevalence of Vitamin D deficiency and insufficiency among healthcare workers and associated risk factors

A total of 25 cross-sectional studies (23–47) focused on the prevalence and risk factors of Vitamin D deficiency among healthcare workers (HCWs) across diverse settings and geographic regions. Research was conducted in Asia (India, Thailand, Pakistan, Qatar, Japan, Israel, Taiwan, Turkey, Saudi Arabia), Europe (Romania, Germany, UK, Iceland, Spain, Turkey) South Africa and America with two more recent focusing on pandemic related Vitamin D deficiency (5). All studies focused exclusively on healthcare workers (HCWs) in alignment with the definition of WHO (22), encompassing a broad spectrum of roles such as physicians, medical residents, dentists, staff nurses, medical students, as well as supportive, technical, and administrative personnel in hospital settings.

Nurses were the most frequently studied professional group with several studies reporting high prevalence of deficiency among shift- working nurses (35) and those with limited sun exposure (28, 41). Physicians and medical residents were also widely represented (39, 40, 42, 43). Two studies examined specific subgroups and medical specialties such as dental staff (26), anesthesiologists (34), dermatology personnel (38). Reported prevalence varied, ranging from approximately 30–90%, influenced by geographic location, season, and professional role. Studies from South Asia and the Middle East generally reported higher deficiency rates compared to European cohorts (24, 31, 32, 45). Seasonal variation was highlighted in Turkish healthcare workers (33), while pandemic-related studies indicated worsening deficiency during COVID-19 (27, 30). Six studies (27, 30, 31, 34, 41, 45) examined specifically sex or gender differences in Vitamin D levels among healthcare professionals. Porojnicu et al. (48) focused on female caregivers in Romania, while Lehnert et al. (35) and Wallingford et al. (28) focused on female nurses, including premenopausal staff and shift-working nurses. Tang et al. (44) studied 95 female nurses, examining associations between fatigue and sleep quality. Jadoon et al. (31) performed gender-specific analysis on 56 doctors and 62 nurses in Pakistan with women reportedly having lower Vitamin D levels due to religious veiling and less sun exposure. Risk factors for deficiency in women included young age, night shifts and irregular schedules, indoor work, poor diet, lack of supplementation, and use of protective clothing (31). Two cross-sectional studies from Thailand and Germany addressed age-related risk for Vitamin D deficiency, with contradictory findings (35, 46). Of note, in nurses, older age combined with night shifts and higher BMI increased risk (35) while among Thai medical students, younger age was associated with lower Vitamin D levels, with fourth-year students having significantly lower levels compared to fifth-year students (46). This suggests that age-related risk may vary by role and lifestyle. Four studies (33, 34, 38, 43) explicitly examined seasonal variation, with most data collected at the end of winter, a period typically associated with lower Vitamin D levels. Skarphedinsdottir et al. (34) reported seasonal deficiency among anesthesia staff, Munter et al. (43) found summer sun exposure to be the strongest predictor of Vitamin D status, Rajatanavin et al. (38) noted high insufficiency among Thai dermatologists despite the summer season. Haliloğlu et al. (33) compared summer and winter levels in Turkish healthcare workers, finding deficiency more common in winter, highlighting the need for seasonal screening and supplementation strategies. Regarding comorbidities diabetes mellitus was reported as one with a prevalence of 26% among 355 HCWs with Vitamin D deficiency (23). Higher BMI was significantly associated with lower Vitamin D levels among female night-shift nurses in Germany (35). Vascular health implications linked with metabolic conditions such as obesity were also reported in Haliloğlu et al. (33) study although this was not the primary aim of the study.

Overall, Vitamin D deficiency prevalence was not pooled into a single global estimate due to substantial heterogeneity across geographic regions, deficiency thresholds, assay methods, and occupational roles.

In South Asia, studies applying <20 ng/mL thresholds reported very high deficiency (e.g., 72–97%), whereas in Sub-Saharan Africa one large cohort reported 28.5% deficiency (<20 ng/mL). In East Asia, prevalence varied by pandemic context and season (e.g., 45.9–90% using <20 ng/mL). European cohorts showed wide variability with strong seasonal effects (e.g., 48.9% end-summer vs. 71.5% winter deficiency in Turkey). Across studies, thresholds differed (<10, <20, <30 ng/mL, and nmol/L-based cutoffs) and assays varied, limiting direct comparability. Nurses and shift workers were frequently studied, with several cohorts reporting high deficiency burdens.

3.2 Vitamin D deficiency and reported health implications for healthcare workers

Thirteen studies have examined how Vitamin D deficiency affects the physical and mental health of healthcare workers (HCWs) (23, 28, 33, 35, 39, 40, 42, 44, 49–53). The health outcomes investigated include immune vulnerability and susceptibility to viral respiratory infections, fatigue, muscle weakness, depression, poor bone health and non- specific musculoskeletal pain, cardiometabolic diseases, neoplasms, highlighting occupational vulnerability. Three studies examined the association of Vitamin D deficiency with cardiovascular and metabolic risks (23, 33, 49). Madani et al. (49) found that among 28% of the included HCWs had obesity, diabetes mellitus and hypertension while Haliloglu et al. (33) found that HCWs had low Vitamin D levels both in summer and winter and medical doctors reported worse endothelial function. Another study found that medical residents have low Vitamin D levels due to limited sun exposure which may affect their triglyceride levels (40). Shift work emerges as a significant determinant, with nurses and other rotating staff showing lower Vitamin D levels and related risks for bone health, skin cancer, mental wellbeing, and hormonal balance (28, 35, 44, 51). HCWs with Vitamin D deficiency showed higher rates of SARS-CoV-2 infection and symptomatic disease, suggesting a potential link between low Vitamin D and immune vulnerability (52). Multani et al. (42), examined the association of low body mass among resident doctors with Vitamin D insufficiency but no correlation was identified. While Manickam et al. (39), found that female physicians with higher BMI demonstrated lower BMI density in the lumbar region along with lower Vitamin D levels. A more recent study revealed that even rapidly rotating clockwise shift work in female healthcare workers can lead to low Vitamin D levels and is also associated with the rise of some hormones, likely associated with stress (51). In addition, although night shift nurses experienced 84.2% fatigue and sleep disturbance and had low Vitamin D levels (96.1%) depression was also present, no significant association was noted with Vitamin D levels (44). Ghammam et al. (53) assessed chronic fatigue among healthcare professionals in a North African university hospital and included serum Vitamin D measurement as a potential biological factor. While Vitamin D deficiency was common, no independent association was detected between serum 25-hydroxyVitamin D levels and chronic fatigue after adjustment, whereas obesity and depressive symptoms were significant correlates (53). Seasonal variation and pandemic-related restrictions further exacerbate deficiency, as observed during COVID-19 (27, 30). A large prospective study of US (50) found that higher circulating 25(OH)D levels may reduce breast cancer risk, particularly in premenopausal women.

3.3 Association between Vitamin D levels and work productivity among healthcare workers

Seven studies examined the relationship between Vitamin D status and work-related outcomes (44, 46, 52, 54–57). Plotnikoff et al. (55) conducted the largest prospective observational study to date, enrolling 10.946 HCWs. Their findings indicated a positive association between serum Vitamin D concentrations and productivity, with markedly lower rates of presenteeism among HCWs maintaining levels of Vitamin D above 40 ng/mL, with modeled estimates suggesting potential payroll savings if deficiency thresholds were addressed. However, the economic projections reported by Plotnikoff et al. (55) should be interpreted with caution as model-based estimates derived from observational associations and assumptions regarding productivity valuation, residual confounding, and generalizability. These findings are hypothesis-generating rather than causal evidence.

In addition, Anuroj et al. (46) reported high fatigue and reduced energy among deficient medical students, suggesting functional impairment and reduced academic or clinical performance. Tang et al. (44) reported high prevalence of fatigue among shift female nurses but no significant associations were established with Vitamin D deficiency.

Accordingly, Villasis Keever et al. (52) found that 69.4% of frontline healthcare workers in Mexico City were Vitamin D deficient, with obesity, diabetes, and occupational sun deprivation identified as key risk factors. This high prevalence suggested increased risks for infection-related absenteeism and reduced physical resilience. Furthermore, three interventional studies (54, 56, 57) demonstrated that high regimens of supplementations of Vitamin D effectively reduced both the incidence and the severity of respiratory viral infections. These outcomes translated into decreased healthcare utilization and fewer sick leave days among participants, underscoring the potential occupational health benefits of maintaining adequate Vitamin D levels and work ability.

3.4 The role of supplementation in addressing Vitamin D deficiency among healthcare workers

Six studies (26, 30, 49, 54, 56, 57) highlighted the necessity of addressing Vitamin D deficiency among health workers and the important role of Vitamin D supplementation. Two interventional studies (54, 57) demonstrated that supplementation reduced COVID-19 incidence and severity, especially in high-dose regimens (57). In addition, supplementation with Vitamin D3 5,000 IU for 9 months reduced the overall incidence of influenza-like illness (54). Ito et al. (30) and Do gruel et al. (26) supported supplementation as a preventive strategy, while Alavi et al. (49) found that Vitamin D supplementation can increase the Vitamin D levels with a notable alleviation of musculoskeletal discomfort in female nurses.

4 Discussion

Although individual studies exist, the literature on Vitamin D status, overall health and productivity among healthcare workers remains fragmented. The review aimed to map the existing evidence, clarify key concepts, identify research gaps, and to inform future study directions A total of 36 studies conducted over the past 15 years were included, with a notable surge during the COVID-19 pandemic (27, 30, 56, 57). Pandemic-era studies (2020 onward) focused on Vitamin D and immune function (COVID-19 susceptibility, severity, and seroconversion), supplementation trials, occupational vulnerability during lockdowns, and reduced sun exposure implicating Vitamin D as modifiable risk factor for infection and presenteeism. This surge reflects three drivers: (i) COVID-19 highlighted Vitamin D role in immune modulation, (ii) HCWs represent a high-risk group, prompting targeted studies, (iii) Increased funding and urgency for workplace health interventions.

Collectively, the evidence underscores a critical yet overlooked issue- Vitamin D deficiency among HCWs- where reported prevalence often surpasses 70%, regardless of geography or climate. Vitamin D deficiency is a global issue, affecting all age groups and regions, highly prevalent in the Middle East, South Asia and among populations with darker skin in northern latitudes (5, 58, 59). Deficiency persists even in sunny regions such as the Mediterranean, underscoring the influence of behavioral and occupational factors over solar exposure. More geographically diverse epidemiological studies are needed, along with ethnic- and sex-specific analyses to address inter- and intra-individual variability (58).

Occupational and environmental factors: indoor work, long shifts, night duties, and limited sun exposure were the most cited determinants. Additional risk factors included female sex, younger age, higher BMI, veiling, and lack of supplementation and use of sunscreen. Seasonal variation was addressed in four studies, all of which confirmed lower Vitamin D levels during winter months, reinforcing the need for seasonal screening protocols (28, 33, 34, 38).

Shift work emerged as the primary occupational determinant (28, 35, 44, 51), and this comes in alignment with the findings of another systematic review and metanalysis that shift workers demonstrate higher risk for Vitamin D hypovitaminosis compared to non- shifters (60). In addition, granted the pleiotropic role of Vitamin D (61) in human body as well the broad spectrum of occupational risks in healthcare settings, associations with other workplace exposures (e.g., chemicals) warrant further investigation.

Vitamin D deficiency was associated with a range of health concerns. Several studies linked low levels to immune dysfunction, including increased susceptibility to respiratory infections and COVID-19 (27, 36, 48, 52, 54, 56, 57). Others explored musculoskeletal health, noting associations with low bone mineral density and osteopenia particularly among young female doctors (39, 42). In addition, low vitamin levels were associated with non- specific musculoskeletal pain in nurses (49). Mental health outcomes such as fatigue, sleep disturbance, and depression were also examined, though findings were mixed (44). While some studies reported high rates of fatigue and poor sleep among deficient individuals, statistical correlations with mental health outcomes were not always significant (46).

Cardiometabolic parameters were also assessed in relation to Vitamin D, showing that medical residents had elevated indices of atherosclerosis and higher triglyceride levels (33). In addition, high prevalence of metabolic syndrome was observed among Vitamin D deficient female nurses (23).

Only a small number of studies directly assessed the impact of Vitamin D status on productivity. One large prospective study found a positive correlation between higher Vitamin D levels and productivity, particularly in reducing presenteeism (55). Other studies suggested indirect effects -such as fatigue and reduced energy- potentially impairing cognitive and physical performance, though these were rarely quantified (44). This highlights a gap in the literature and underscores the need for more targeted research on the issue.

Four studies, including two randomized controlled trials (49, 54), evaluated the role of Vitamin D supplementation among HCWs. Findings consistently indicated beneficial effects, particularly in reducing COVID-19 severity and improving immune resilience. Phelan et al. (62) advocates for recognizing Vitamin D deficiency as a modifiable occupational risk factor, urging institutional policies to include regular monitoring and supplementation programs. Accordingly, Dogruel et al. (26) recommends Vitamin D supplementation along with increase of sun exposure as preventative measures for vulnerable dental staff. While not always reducing infection rates, supplementation—especially at higher doses—may reduce symptom severity and improve immune resilience. Supplementation was well-tolerated and effective in normalizing serum levels, especially in high-dose regimens. A consensus statement further supported routine screening and supplementation in high-risk occupational groups, including HCWs (10).

Serum 25-hydroxyVitamin D concentrations above 30 ng/mL (75 nmol/L) have been associated with reduced risk for major chronic diseases such as including cardiometabolic, infectious and neurodegenerative diseases (20, 63). Currently, no supplementation is suggested for adult population, unless they belong to certain high-risk groups (10). Despite growing interest, significant gaps remain. Few studies assessed direct links between Vitamin D status and job performance, absenteeism, or cognitive functioning (55). Evidence on long-term outcomes and cost-effectiveness of supplementation programs is limited. Additionally, most research focused on nurses and physicians, neglecting other HCW categories such as technicians, administrative staff, and paramedics. Geographic and ethnic variability, as well as sex-specific differences, require further investigation to inform tailored interventions. The key domains that need further exploration on healthcare workers are those in terms with immune system modulation and the vulnerability for infections, mental health and fatigue as well as comorbidities undermining the work functioning and productivity. Although studies suggest a link between low Vitamin D and mood disorders (18), neurodegenerative diseases as well sleep disorders there is little attention to the occupational groups (20). The review supports a highly promising field of research: the broader role of micronutrients in promoting wellbeing and productivity of healthcare workers (15, 16, 64).

This review offers valuable insights but is subject to notable limitations. First, the absence of prospective protocol preregistration represents a methodological limitation. However, the review followed a predefined PCC framework and PRISMA-ScR guidance, and its methodology was established a priori and applied consistently throughout.

Since most studies employed a cross-sectional design, causal relationships cannot be established. Sample sizes varied widely, and demographic or methodological data were often incomplete. Few studies included quality assessments, and definitions of deficiency or measurement techniques lacked standardization. Interpretation of Vitamin D status across included studies was influenced by variability in the thresholds used to define deficiency. In the present review, the <12 ng/mL cut-off referenced in the Introduction reflects the National Academy of Medicine (NAM) definition of Vitamin D deficiency, which is primarily based on skeletal health outcomes. In contrast, most included studies applied a < 20 ng/mL threshold, consistent with thresholds commonly used in epidemiological research and clinical practice. This variability mirrors the lack of universal consensus regarding optimal 25-hydroxyVitamin D cut-offs, with definitions differing across scientific bodies, research contexts, and regional guidelines. Such heterogeneity complicates direct comparison of prevalence estimates and outcome associations across studies and should be considered when interpreting the findings (see Supplementary Table S3). In addition, substantial heterogeneity was observed in Vitamin D assay methods across studies (liquid chromatography–tandem mass spectrometry (LC–MS/MS), chemiluminescent immunoassay (CLIA), electrochemiluminescence immunoassay (ECLIA), high-performance liquid chromatography (HPLC), and radioimmunoassay (RIA)), which may contribute to variability in reported concentrations and prevalence estimates. Differences in analytical performance and calibration further limit direct inter-study comparability.

Broader research across different specialties could uncover occupational differences and risk patterns. Nurses were the most studied group among healthcare workers (28, 31, 35, 37, 41, 44, 46, 49, 51, 52) with women overrepresented—likely reflecting the workforce composition and greater willingness for participation in health-related research (65, 66). However, some evidence suggests young males may be particularly vulnerable to deficiency (38, 46, 62). In addition, most studies focus primarily on physicians and nurses. This narrow focus fails to represent the full spectrum of HCWs, such as administrative staff, technicians, paramedics, scientific and support personnel. Aside from the general observations mentioned earlier, no further evaluation of study quality or risk of bias was conducted. This was because the primary aim was to map the breadth and the scope of the existing literature. Additionally, while the 15-year time limit was considered appropriate, this temporal limitation may have excluded important earlier developments in the field. Moreover, due to the cross-sectional design of most of the included studies, causality could not be inferred. Low Vitamin D may contribute to fatigue, musculoskeletal symptoms, and reduced work functioning, but reverse causality is plausible: individuals with poorer health, higher BMI, reduced outdoor activity, or more demanding shift patterns may both have lower Vitamin D and worse outcomes. Key confounders include BMI/adiposity, physical activity, comorbidities, smoking, dietary intake, supplementation, sun-avoidance behaviors, and seasonality.

Despite these limitations, the consistency of findings across diverse settings strengthens the overall conclusions. Given the high prevalence of Vitamin D deficiency reported across healthcare worker populations, future research should prioritize the evaluation of targeted screening strategies, including the identification of subgroups most likely to benefit from assessment and intervention. In addition, well-designed prospective studies and randomized controlled trials are needed to clarify whether Vitamin D supplementation confers measurable benefits on health-related outcomes, work performance, and productivity in this occupational group. Particular attention should be given to optimal dosing strategies, duration of supplementation, and potential modifiers such as baseline Vitamin D status, seasonality, and occupational exposures.

5 Conclusion

This scoping review maps the available evidence on Vitamin D status in healthcare workers and highlights consistently reported Vitamin D inadequacy across many occupational settings. However, the existent literature is heterogeneous in deficiency thresholds, assay methods, and sampling season, limiting direct comparability between studies.

Evidence gaps remain substantial, particularly with respect to productivity outcomes. Standardized measures of presenteeism and absenteeism are infrequently applied, and causal inference is constrained by the predominance of cross-sectional study designs. Accordingly, rather than issuing direct clinical or policy recommendations, this scoping review identifies key priorities for future research. These include longitudinal and implementation studies evaluating targeted workplace interventions, as well as harmonized approaches to measurement and reporting. Future research should also emphasize prospective and interventional designs that assess clinically and occupationally meaningful outcomes, while further exploring the evolving role of micronutrients in supporting the health, wellbeing, and productivity of healthcare workers.

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