We read with great interest the article by Haque et al () published recently in Arthritis Care & Research. The authors provide the first study investigating the association between vitamin D levels and several cardiovascular risk factors in patients with rheumatoid arthritis (RA). Although the study results support the hypothesis that vitamin D may contribute to increased cardiovascular risk observed in RA patients, we believe that these findings should be critically reviewed, taking into consideration the following issues.
First, a large amount of recent evidence indicates there is an association between vitamin D levels and obesity (), which is an established cardiovascular risk factor. However, body mass index (BMI) and waist circumference were considered only as potential confounding factors in the statistical analysis of the study by Haque et al. Thus, it would be interesting to know whether vitamin D levels were associated with the presence of obesity and/or metabolic syndrome in RA patients.
Second, impaired renal function, which significantly affects vitamin D levels and is commonly observed in RA patients (), was not included in the present analysis as a possible confounding factor. Furthermore, it should be noted that no association was found between vitamin D levels and systolic or diastolic blood pressure levels in this population, which is in contrast with experimental () and cross-sectional data () linking vitamin D deficiency with hypertension.
Finally, after adjusting for potential confounders, the vitamin D levels were associated with only high-density lipoprotein cholesterol, E-selectin, and soluble intercellular adhesion molecule 1 (sICAM-1) levels. However, E-selectin and sICAM-1 have been investigated in earlier studies as humoral markers of endothelial dysfunction and atherosclerosis, but their role in cardiovascular risk stratification has not been established ().
In conclusion, it is our opinion that well-designed prospective studies are needed to further investigate the role of vitamin D as a marker of cardiovascular risk in patients with RA. In addition, even if vitamin D is independently associated with cardiovascular risk in RA patients, whether the measurement of vitamin D levels can add something more to our knowledge of the risk stratification in these patients needs to be clarified. Nevertheless, the promising therapeutic opportunity of vitamin D supplementation has not been confirmed by randomized studies in patients with excessive cardiovascular risk.