This study is a cross-sectional study that collected physical examination data of healthcare professionals at Shanxi Bethune Hospital from January to March 2022. The primary aim of this study is to compare the vitamin D deficiency status between doctors and nurses. All personal privacy information was removed before analysis.

All on-duty healthcare professionals without malignant diseases during the physical examination.

The inclusion criteria for hospital staff physical examination records were enrolled.

The exclusion criteria for hospital staff physical examination records were enrolled.

This study was approved by the Institutional Ethical Review Board of Shanxi Bethune Hospital (No. YXLL-2023-185, YXLL-SL-2022-221), according to the ethical guidelines of the Helsinki Declaration. All hospital staff signed Informed consent for clinical data use. As all data utilized in this study were anonymized, the requirement for informed consent was therefore waived.

Due to the stable nature of serum 25-hydroxyvitamin D (25-(OH)D), it is used as a marker for vitamin D status. Although there is controversy over using these cut-off values to define vitamin D deficiency, most agree that vitamin D levels <20 ng/mL (50 nmol/L) are considered deficient, 21 - 29 ng/mL (52 - 72 nmol/L) are considered insufficient, and >30 ng/mL (75 nmol/L) are considered sufficient 20. The IOM DRI committee in the United States suggested that people are at risk of deficiency at serum 25(OH)D concentrations <12 ng/mL (30 nmol/L).At the same time, studies have used the most conservative serum 25(OH)D threshold of <10/12 ng/mL (25/30 nmol/L) 8. This study used the enzyme-linked immunosorbent assay (ELISA) to measure [25(OH)D]. The range provided in the reagent instructions is <12.3 ng/mL (30.75 nmol/L) 19.

Besides basic information such as height, weight, gender, age, and blood pressure, we also collect other laboratory indicators from participants, including thyroid-stimulating hormone (TSH), Free triiodothyronine (FT3), Free thyroxine (FT4), low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), UA, cholesterol (CHO), triglycerides (TG), and glucose (Glu). In addition, there are job-related factors such as involvement in surgical procedures and exposure to radiation.

The demographic informations of all participants are listed in Table 1. A significant disparity in sex is observed, with 39.14% of LPs being male compared to 6.59% among nurses (P<0.001). LPs tend to be older, with a mean age of 36.89 years, while nurses have a mean age of 33.33 years (P<0.001). The mean BMI is higher for LPs (23.97 kg/m²) compared to nurses (22.64 kg/m²) (P<0.001). A larger proportion of nurses fall within the normal BMI range (66.54%) compared to LPs (52.80%), whereas more LPs are classified as overweight or obese (44.74% vs. 29.27%) (P<0.001). The incidence of hypertension is greater among LPs (32.57%) compared to nurses (22.23%) (P<0.001). Additionally, nurses are more frequently involved in surgical-related work (48.73% vs. 41.45%) (P<0.001) but have less radiation exposure (3.44% vs. 19.74%) (P<0.001) compared to LPs.

hows the laboratory testing results for health professionals. There are no significant differences in FT3 and FT4 levels between the groups, with both having a mean FT3 of 3.70pg/mL and FT4 of 0.86 ng/dL. However, the median TSH level is 2.24 μIU/mL for LPs and 2.38 μIU/mL for nurses which shows significant difference. (P=0.0165). LDL-C levels are higher in LPs (3.05 mmol/L) compared to nurses (2.81 mmol/L) (P<0.001), while HDL-C levels are lower in LPs (1.36 mmol/L) compared to nurses (1.41 mmol/L) (P<0.001). The median UA level is higher in LPs (291.9 μmol/L) than in nurses (255.5 μmol/L) (P<0.001). CHO levels are higher in LPs (4.75 mmol/L) compared to nurses (4.49 mmol/L) (P<0.001). Glc levels are also higher in LPs (4.99 mmol/L) compared to nurses (4.80 mmol/L) (P<0.001). TG levels are higher in LPs, with a median of 1.03 mmol/L compared to 0.82 mmol/L in nurses (P=0.0001). The median vitamin D level is slightly higher in LPs (9.4 ng/mL) compared to nurses (8.7 ng/mL) (P=0.0001), but both groups exhibit a high prevalence of vitamin D deficiency, with 78.12% of LPs and 85.63% of nurses affected (P<0.001) (Figure 2).

Table 3 shows the results of logistic regression analysis of vitamin D deficiency.

The univariable analysis identifies several factors associated with vitamin D deficiency among health professionals. Age over 30 years is linked to a lower likelihood of vitamin D deficiency (OR=0.61, 95% CI 0.45-0.82, P=0.001). Job category is also a significant factor, with nurses more likely to have vitamin D deficiency compared to LPs (OR=1.67, 95% CI 1.30-2.13, P<0.001). BMI within the normal range serves as the reference group, with underweight individuals (BMI <18) showing an OR of 1.97 (P=0.119) and overweight individuals (BMI >24) showing an OR of 0.72 (P=0.010). UA levels below the normal range are associated with an increased risk of vitamin D deficiency (OR=1.53, P=0.026), whereas UA levels above the normal range show a decreased risk (OR=0.53, P=0.009). CHO levels below (OR=0.68, P=0.221) and above (OR=0.72, P=0.025) the normal range are not significant. The other factors examined, TSH levels, FT3 levels, FT4 levels, LDL-C levels, TG levels, Glc levels, hypertension, engagement in surgery-related work, and radiation exposure did not exhibit a significant association with the prevalence of vitamin D deficiency.

The multivariable analysis further refines the associations between various factors and vitamin D deficiency. Age over 30 years continues to be associated with a lower likelihood of vitamin D deficiency (OR=0.68, 95% CI 0.50-0.92, P=0.013). Job category remains a significant factor, with nurses still more likely to have vitamin D deficiency compared to LPs (OR=1.26, 95% CI 1.10-1.44, P=0.001). UA levels below the normal range continue to show an increased risk of vitamin D deficiency (OR=1.51, P=0.034), while UA levels above the normal range show a decreased risk (OR=0.57, P=0.048).

The rest of other factors examined, including TSH levels, FT3 levels, FT4 levels, LDL-C levels, CHO levels, TG levels, BMI, Hypertension, engagement in surgical relevant work, and radiation exposure are also not significantly associated with vitamin D deficiency.

Table 4 presents the IPTW data set for health professionals, comparing LPs and nurses across various parameters and all the variables are well-balanced with SMD from 0.001 to 0.083, p-values from 0.152 to 0.983.

Table 5 compares the prevalence of vitamin D deficiency between LPs and nurses using the IPTW data set. The results indicate that vitamin D deficiency is prevalent in both groups but higher among nurses. Specifically, 78.02% of LPs are affected by vitamin D deficiency, compared to 83.41% of nurses (P=0.032). This statistically significant difference suggests that, even after adjusting for various confounding factors using IPTW, nurses are more likely to experience vitamin D deficiency compared to LPs.

Table 2

		Overall (n=1,944)	LP (n=608)	Nurse (n=1,336)	Statistics	P-value
TSH (μIU/mL)	median (q1-q3)	2.34 (1.64~3.25)	2.24 (1.61~3.10)	2.38 (1.67~3.35)	χ2=10.253	0.0165
FT3 (pg/mL)	mean ± sd	3.70 ±0.46	3.70 ±0.40	3.70 ±0.49	F=2.45	0.062
FT4 (ng/dL)	mean ± sd	0.86 ±0.15	0.87 ±0.13	0.86 ±0.16	F=0.52	0.670
LDL-C (mmol/L)	mean ± sd	2.89 ±0.65	3.05 ±0.65	2.81 ±0.64	F=31.73	< 0.001
HDL-C (mmol/L)	mean ± sd	1.39 ±0.29	1.36 ±0.30	1.41 ±0.29	F=12.14	< 0.001
UA (μmol/L)	median (q1-q3)	265 (225.9~318.3)	291.9 (236.3~369.7)	255.5 (219.9~298.6)	F=76.40	< 0.001
CHO (mmol/L)	mean ± sd	4.57 ±0.84	4.75 ±0.82	4.49 ±0.84	F=21.40	< 0.001
TG (mmol/L)	median (q1-q3)	0.87 (0.65~1.27)	1.03 (0.76~1.54)	0.82 (0.62~1.15)	χ2=137.839	0.0001
Glc (mmol/L)	mean ± sd	4.86 ±0.72	4.99 ±0.88	4.80 ±0.63	F=10.07	< 0.001
Vitamin D (ng/ml)	median (q1-q3)	8.9 (7.40~11.00)	9.4 (7.70~11.62)	8.7 (7.30~10.60)	χ2=-5.89	0.0001
	min-max	6.50 - 43.70	6.50 - 40.00	6.50 - 43.70
Vitamin D deficiency		1619 (83.28%)	475 (78.12%)	1144 (85.63%)	χ2=34.43	<0.001

LP: Licensed physicians; TSH: thyroid stimulating hormone; FT3: free thyroxine 3; FT4: free thyroxine 4; LDL-C: low-density lipoprotein cholesterol, HDL-C: high-density lipoprotein cholesterol; UA, uric acid; CHO: cholesterol; TG: triacylglycerol; Glc: glucose.

Figure 2

Table 3

			Univariable analysis		Multivariable analysis
		Number (%)	OR (95%CI)	P-value	OR (95%CI)	P-value
Sex	female	1618 (83.23%)	1.27 (0.94, 1.72)	0.123	0.72 (0.49, 1.07)	0.101
Age	>30	1416 (72.84%)	0.61 (0.45, 0.82)	0.001	0.68 (0.50, 0.92)	0.013
Job category	LP	608 (31.28%)	1
	Nurse	1336 (68.72%)	1.67 (1.30, 2.13)	<0.001	1.26 (1.10, 1.44)	0.001
TSH (μIU/mL)	within normal range (0.56-5.91)	1809 (93.06%)	1.0
	subpar to normal range (≤0.56)	54 (2.78%)	0.63 (0.33, 1.19)	0.154
	superior to normal range (≥5.91)	81 (4.17%)	1.27 (0.66, 2.43)	0.469
FT3 (pg/mL)	within normal range (2.30-4.80)	1913 (98.41%)	1.0
	superior to normal range (≥4.80)	31 (1.59%)	1.04 (0.40, 2.74)	0.929
FT4 (ng/dL)	within normal range (0.59-1.25)	1897 (97.58%)	1
	subpar to normal range (≤0.59)	32 (1.65%)	0.71 (0.30, 1.66)	0.430
	superior to normal range (≥1.25)	15 (0.77%)	0.80 (0.22, 2.84)	0.726
BMI (kg/m2)	18-24	1210 (62.24%)	1
	<18	71 (3.65%)	1.97 (0.84, 4.61)	0.119	1.62 (0.68, 3.83)	0.276
	>24	663 (34.10%)	0.72 (0.57, 0.93)	0.010	0.84 (0.64, 1.10)	0.213
Hypertension		495 (25.46%)	0.82 (0.63, 1.07)	0.153
LDL-C (mmol/L)	within normal range (<3.37)	1531 (78.76%)	1
	superior to normal range (≥3.37)	413 (21.24%)	0.76 (0.58, 1.01)	0.055	1.10 (0.68, 1.77)	0.705
HDL-C (mmol/L)	within normal range (1.03-1.55)	1249 (64.25%)	1
	subpar to normal range (≤1.03)	164 (8.44%)	1.14 (0.72, 1.78)	0.578
	superior to normal range (≥1.55)	531 (27.31%)	1.03 (0.78, 1.35)	0.836
UA (μmol/L)	within normal range (208-428)	1551 (79.78%)	1
	subpar to normal range (≤208)	304 (15.64%)	1.53 (1.05, 2.22)	0.026	1.51 (1.03, 2.22)	0.034
	superior to normal range (≥428)	89 (4.58%)	0.53 (0.32, 0.85)	0.009	0.57 (0.33, 0.99)	0.048
CHO (mmol/L)	within normal range (3.25-5.2)	1484 (76.34%)	1
	subpar to normal range (≤3.25)	66 (3.40%)	0.68 (0.37, 1.26)	0.221	0.61 (0.33, 1.13)	0.115
	superior to normal range (≥5.2)	394 (20.27%)	0.72 (0.55, 0.96)	0.025	0.80 (0.50, 1.28)	0.354
TG (mmol/L)	within normal range (≤1.7)	1680 (86.42%)	1
	superior to normal range (＞1.7)	264 (13.58%)	1.07 (0.75, 1.53)	0.705
Glc (mmol/L)	within normal range (3.9-6-1)	1875 (96.45%)	1
	subpar to normal range (≤3.9)	28 (1.44%)	1.19 (0.41, 3.46)	0.745
	superior to normal range (≥6.1)	41 (2.11%)	0.62 (0.30, 1.27)	0.190
Surgical relevant work		903 (46.45%)	1.16 (0.91, 1.48)	0.225
Radiation exposure		166 (8.54%)	0.79 (0.53, 1.18)	0.255

LP: Licensed physicians; TSH: thyroid stimulating hormone; FT3: free thyroxine 3; FT4: free thyroxine 4; LDL-C: low-density lipoprotein cholesterol, HDL-C: high-density lipoprotein cholesterol; UA, uric acid; CHO: cholesterol; TG: triacylglycerol; Glc: glucose; OR: odds ratio; CI: confidence interval.

Despite the widespread prevalence of vitamin D deficiency, certain groups such as healthcare professionals face a higher risk. In this study, factors related to vitamin D deficiency among them in a tertiary hospital were significantly associated with age, job type, and UA levels.

This study indicates that age is a factor associated with vitamin D deficiency in healthcare professionals. Individuals over 30 years old are less likely to develop this condition. A study conducted in the United States shows older age is a protective factor for vitamin D deficiency 21. A study in South Korea shows that nurses in their 30s have higher vitamin D levels compared to nurses in their 20s 18. This may be because young people prefer ordering food delivery 22. Such as quick and convenient food choices, these foods lack natural sources of vitamin D such as fatty fish, egg yolks, and fortified dairy products 23. Therefore, an unbalanced diet can significantly reduce the efficiency of vitamin D absorption, leading to lower vitamin D levels in the body 24.

This study shows that the prevalence of vitamin deviancy is higher among nurses than that of LPs. An important factor is significantly related to the work environment and nature of their jobs. Although both participate in shift work, nurses' rotating shifts are more common 25. Nurses' work content is usually more intensive and varied, including 24-hour continuous bedside care, medication management, and emotional support for patients. In contrast, licensed physicians focus more on diagnosis and treatment and do not engage in 24-hour direct care, resulting in a lower frequency of shift work 26. A study in Korea exploring environmental and occupational factors associated with vitamin D deficiency found that shift work was significantly related to vitamin D deficiency 27. A systematic review by Luca Coppeta et al. also mentioned that shift workers have consistently been reported as the occupational group most likely to be deficient in vitamin D3 28. Shift work including early mornings, partial nights, or overnight shifts, thus it can lead to significantly reduced outdoor activities and daytime sunlight exposure, affecting vitamin D synthesis 29. Furthermore, the night shift conditions for licensed physicians differ from those for nurses. Licensed physicians on night duty in the wards can sleep, whereas nurses on duty cannot, resulting in different sleep conditions. Research shows that lack of sleep and disruption of circadian rhythms affect the secretion of various hormones in the body, including those that influence vitamin D metabolism 30.

Based on our published study, nurses often experience shorter sleeping hours and longer working hours per day compared to LPs 31. Nurses not only work long hours but also handle a large number of direct patient care tasks that demand high physical and mental investment 32. Studies have shown that high stress and long working hours can lead to irregular eating, further reducing vitamin D intake and can easily result in a suboptimal health status 33, 34.

This presented study also found that lower-than-normal UA levels were associated with an increased risk of vitamin D deficiency. Vitamin D is transported in the blood (bound to vitamin D-binding protein) to the liver, where it is hydroxylated to 25-hydroxyvitamin D (25-(OH)D), which is further converted to 1α,25-dihydroxyvitamin D (1α,25-(OH)2D) 35. High uric acid inhibits 1 alpha-hydroxylase, leading to a decrease in 1,25-dihydroxyvitamin D (1,25(OH)2D), which in turn causes a relative increase in 25-(OH) D concentration 36, 37, 38. Another possible reason is UA is a potent antioxidant, and higher UA levels can reduce oxidative stress, thereby reducing the consumption of vitamin D 39. High uric acid levels are generally associated with the consumption of seafood and meat, which are also sources of dietary vitamin D 40, 41.

In this cross-sectional study, we compared the vitamin D status of healthcare professionals during the same physical examination period, and it was indeed found that there is a high prevalence of vitamin D deficiency. Meanwhile, nurses are more likely to experience vitamin D deficiency due to various factors related to their work environment, job nature, and lifestyle. To improve the health status of nurses, it is recommended to adopt multi-level intervention measures, such as increasing sunlight exposure, improving the work environment, providing psychological support, enhancing health education, and conducting regular health check-ups. It is also recommended to strengthen monitoring of vitamin D deficiency and use reasonable supplementation measures to increase their vitamin D levels. This not only helps to improve the health of nurses but also enhances the overall quality of healthcare services.

Our study has several limitations. First, we do not know the frequency of night shifts for each individual before the physical examination, nor do we know their rest conditions during the night shifts. Additionally, we are not aware of each person's specific dietary habits or whether they took vitamin supplements before the examination. Hope further studies can be implemented to answer such questions.

Healthcare professionals generally lack vitamin D, and nurses are more deficient than licensed physicians.