Association of vitamin D level with systemic lupus erythematosus: A case-control study

Background: Systemic lupus erythematosus (SLE) is a chronic autoimmune connective tissue disease. SLE patients are more prone to vitamin D deficiency because of their light sensitivity, renal involvement, and prolonged steroid use. This current study aimed to determine the relationship between vitamin D deficiency and SLE.
Methods: In this case-control study, 50 SLE patients (cases) and 50 healthy people (controls) were recruited. The reference value of vitamin D is as follows: normal ≥ 30 ng/ml, deficient ≤ 20 ng/ml, and insufficient 21–29 ng/ml.
Results: The mean (standard deviation) of vitamin D levels in SLE patients was 19.5 (5.3) ng/mL, which was significantly lower than those in healthy controls, 27.3 (10.0) ng/mL (P<0.001). The healthy controls had a higher proportion of people with normal vitamin D levels (≥ 30 ng/ml). We noticed a moderate negative correlation between vitamin D levels and fatigability, while a moderate positive correlation was seen with hemoglobin levels and the duration of sun exposure. However, in multiple logistic regression analysis, all the associations mentioned above disappeared.
Conclusion: Although vitamin deficiency was found to be associated with SLE, its relationship disappears when the confounding by other variables is considered in the analysis. 


INTRODUCTION
Systemic lupus erythematous (SLE) is a common multisystemic autoimmune disease among Bangladeshi females.The relationship between vitamin D and SLE was first described in 1995 after discovering vitamin D receptors expressed by immune cells. 1 As in other autoimmune diseases, vitamin D deficiency (VDD) could be one of the factors that may regulate SLE disease activity. 24][5][6] VDD is common in SLE because of the avoidance of sun exposure owing to photosensitivity, use of sun protectors, second chronic renal insufficiency of lupus nephritis, and use of glucocorticoids and hydroxychloroquine medications that enhance the clearance of vitamin D. 7 Researchers of previous studies have tried to establish the prevalence of VDD and its significance in various clinical aspects such as SLE disease activity, fatigability, and laboratory parameters. 8,9  question that is yet to be answered is whether VDD indeed alters the course and prognosis of SLE.The answer to this query has a tremendous clinical impact on SLE treatment to potentiate therapeutic possibilities with vitamin D supplementation. 10,11 ardless of whether VDD is a cause or consequence or both in SLE, its importance is almost undeniable.It is expected that vitamin D levels may differ among populations of different latitudes.Effects of vitamin D on SLE disease course represent an interesting area of

Study design
This case-control study was conducted in the

Data collection
Participants were interviewed using a semi-structured

Data analysis
Data were analyzed using SPSS software, version 23.
Continuous variables were expressed by mean and standard deviation (SD).Qualitative data were presented as numbers and percentages.Analysis was performed with the reference value of vitamin D: normal ≥ 30 ng/mL, insufficient 21-29 ng/mL, and deficient ≤ 20 ng/mL. 12Quantitative variables were compared using t test, and categorical data were compared using chi-square test.Pearson correlation was used to check the relationship between two continuous variables.Statistical significance was set at

RESULTS
The mean (SD) age of cases and controls were 25.

DISCUSSION
This case-control study observed a difference in the vitamin D levels among SLE patients compared to the healthy controls.However, all the differences disappeared after adjustment for the potential confounding by the available variables.A similar observation was identified in an Indian case-control study. 13Similar findings were observed in Saudi Arabia, China, and Bahrain. 6,14In an Egyptian study, researchers showed that their control group had optimal vitamin D levels (79.0 ng/mL), significantly higher than the SLE group (17.6 ng/mL). 10 Surprisingly, younger participants of both cases and controls had lower vitamin D levels than the older participants.This may be due to multiple factors that vary from person to person, e.g., season, sun exposure, and skin complexion.However, a large study from Lebanon found that older adults are more vitamin D deficient. 15,16  lower vitamin D level in women might be attributed to their lifestyle, similar to the findings of another study on female garment workers. 4The people in rural areas are supposed to have more exposure to the sun.As a result, their vitamin D level should be higher than those   living in urban areas.Surprisingly, we found a lower level of vitamin D among rural people.8] In the current study, the individuals with less sun exposures had significantly lower vitamin D levels among both groups.But the differences did not persit when confounding by other variables were considered.Disease activity levels might be one of the major contributors to this. 7,8,10 Hwever, there are conflicting studies 11,14 that warrants resolution using well-designed studies.

Conclusions
Although this study's representativeness is limited, we conclude that the SLE cases had lower levels of vitamin D. However, adjustment of the differences by potential confounders eliminated this difference.Given that studies around the world provided conflicting findings, a well-designed study ensuring representation of the cases and controls might provide a workable solution.
questionnaire.Diagnostic information, clinical and laboratory, were recorded.Four ml of venous blood was obtained from each participant in an 8-hour fasting state.Measurements of an inactive form of vitamin D3-25(OH)D levels in their sera were measured.The SLEDAI score was calculated based on patients' last 10day clinical and lab parameters.The scoring system of SLE consisted of 105 points.The scores were categorized into (a) remission or no flare (scores 0-3), low (3-6), moderate (6-12), and high (>12) disease activity.Fatigue severity was assessed by a fatigue severity scoring system of seven questions (each question carried one point).

FIGURE 1
FIGURE 1 Vitamin D status among the case and controls (n=100)

TABLE 1 Vitamin D level (ng/ml) according to socio-demographic, clinical, and laboratory characteristics of the cases and controls
Saha M et al.Bangabandhu Sheikh Mujib Medical University Journal 2023; https://doi.org/10.3329/bsmmuj.v16i4.68428Vitamin D in patients with SLE 220

Mean (standard deviation) of vitamin D level (ng/mL)
*The Chi-square or t test, as appropria