Background Numerous studies have demonstrated that inadequate vitamin D levels are common in systemic lupus erythematosus (SLE) patients and they correlate inversely with disease activity. To date, there is paucity of data on the prevalence of vitamin D status, as well as its clinical and immunological associations in Malaysian SLE patients.

Objectives Our study aimed to determine the prevalence of vitamin D deficiency and insufficiency in SLE patients, and to examine the associations between vitamin D status with gender, ethnic groups, clinical manifestations of SLE, Schirmer's test, cardiovascular risk factors, bone mineral density and autoantibodies.

Methods This retrospective study included 216 SLE patients who attended the Rheumatology Clinic of Kuala Lumpur Hospital between January 2013 and December 2015. Data was obtained from patients' medical records. All patients fulfilled the 1997 American College of Rheumatology revised classification criteria for SLE. Serum 25(OH)D concentrations were measured by electrochemiluminescence immunoassay.

Results A total of 216 SLE patients were included in this study. Eleven (5.1%) were males and 205 (94.9%) were females. There were 141 (65.3%) Malay, 53 (24.5%) Chinese, 19 (8.8%) Indian and 3 (1.4%) of other ethnic group. This corresponded with the pattern of ethnic distribution in the Malaysian population. Their ages ranged from 14 to 75 years, with a mean age of 35.9±7.1 years. Mean duration of SLE at the time of 25(OH)D analysis was 6.9 years (range from 0 to 39 years), and mean age was 35.1±6.4 years (range from 14 to 75 years). Mean 25(OH)D concentration was 51.3±14.8 nmol/L (range from 7.5 to 156.1 nmol/L). Fifty (23.1%) patients had vitamin D deficiency, 120 (55.6%) had vitamin D insufficiency, while 46 (21.3%) had adequate vitamin D levels.

Our study showed statistically significant association between vitamin D status and ethnic group (p<0.001). The Chinese ethnic group had the lowest proportion of patients with vitamin D deficiency and insufficiency (60.4%), while Malay had the highest proportion at 86.5%. Mean levels of serum 25(OH)D in Chinese, Indian and Malay SLE patients were 66.3±36.7 nmol/L, 54.9±36.4 nmol/L, and 45.0±27.5nmol/L, respectively. Among the clinical manifestations of SLE, only lupus nephritis showed a statistically significant association with vitamin D status (p<0.001). In terms of cardiovascular risk factors, hypertension demonstrated significant correlation with vitamin D status (p=0.032).

No significant association was found between vitamin D status and gender. Nonetheless, male SLE patients had higher mean 25(OH)D concentrations at 69.4±36.9 nmol/L, compared to female at 50.2±31.6 nmol/L. There were no significant correlations between vitamin D status and clinical features of lupus such as cutaneous lesions, arthritis and NPSLE; positive Schirmer's test; cardiovascular risk factors, that are, dyslipidemia and diabetes mellitus; osteoporosis; and autoantibodies which included anti-dsDNA antibody, anti-Ro antibody, anticardiolipin antibody and rheumatoid factor.

Conclusions Sub-optimal vitamin D levels are prevalent among SLE patients in a tropical country and are associated with ethnic group, lupus nephritis and hypertension. It is essential to include vitamin D supplementation in the management of SLE patients.

References

1. Toloza SMA, Cole DEC, Gladman DD, et al. Vitamin D insufficiency in a large female SLE cohort. Lupus 2010;19: 13–19.

References

Disclosure of Interest None declared