Vitamin D: something new under the sun

Vitamin D and Arterial Hypertension: Facts and Myths

PURPOSE OF REVIEW

Vitamin D and its derivatives are biologically active fat-soluble steroid hormones, which are transcription factors for numerous genes. The results of several observational studies suggest the relationship between plasma concentration of vitamin D and the risk of arterial hypertension, as well as between the intensity of insolation and the risk of arterial hypertension.

RECENT FINDINGS

Based on the results of the abovementioned studies, it was hypothesized that vitamin D is characterized by the antihypertensive properties. Animal experiments have shown that vitamin D reduces activity of the renin-angiotensin-aldosterone system and improves vasorelaxation of blood vessels. Results of clinical studies did not confirm these results. Moreover in interventional clinical trials, it was documented that supplementation of vitamin D did not reduce blood pressure. The influence of exposure to sunshine at different wave lengths on blood pressure was examined in clinical studies and it was found that ultraviolet A radiation (UVA) lead to the release of nitric oxide from the skin. This might explain lower level of blood pressure in subjects from the regions with a higher rate of insolation. The aim of this review is to summarize current knowledge concerning the relationship between vitamin D and arterial hypertension based on both observational and interventional studies.

Vitamin D and Cardiovascular Risk in Children

OBJECTIVE

Vitamin D is a group of fat-soluble molecules that are structurally similar to steroids. Emerging data have led to the hypothesis that Vitamin D plays a role in the regulation of many physiological processes beyond calcium and phosphorus homeostasis. With this review, we aimed to summarize the changes in Vitamin D levels in children with cardiovascular diseases based on the literature. In addition, we also reviewed the potential mechanisms underlying cardiovascular diseases associated with Vitamin D deficiency or insufficiency.

DATA SOURCES

The articles in English were searched from PubMed (1968-2016) and EMBASE (1991-2016), with the keywords of "Vitamin D AND cardiovascular diseases" and "Vitamin D AND children."

STUDY SELECTION

Original articles and critical reviews about Vitamin D and cardiovascular risk in children were selected for review. Researches focused on adults were excluded.

RESULTS

Studies have shown that several pediatric cardiovascular diseases may be associated with Vitamin D deficiency or insufficiency, including hypertension, orthostatic intolerance, and Kawasaki disease.

CONCLUSIONS

Vitamin D may play a role in the regulation of the cardiovascular system. Further investigation would hopefully disclose the usefulness of Vitamin D as a biomarker for cardiovascular diseases in children.

What is the optimal level of vitamin D in non-dialysis chronic kidney disease population?

AIM

To evaluate thresholds for serum 25(OH)D concentrations in relation to death, kidney progression and hospitalization in non-dialysis chronic kidney disease (CKD) population.

METHODS

Four hundred and seventy non-dialysis 3-5 stage CKD patients participating in OSERCE-2 study, a prospective, multicenter, cohort study, were prospectively evaluated and categorized into 3 groups according to 25(OH)D levels at enrollment (less than 20 ng/mL, between 20 and 29 ng/mL, and at or above 30 ng/mL), considering 25(OH)D between 20 and 29 ng/mL as reference group. Association between 25(OH)D levels and death (primary outcome), and time to first hospitalization and renal progression (secondary outcomes) over a 3-year follow-up, were assessed by Kaplan-Meier survival curves and Cox-proportional hazard models. To identify 25(OH)D levels at highest risk for outcomes, receiver operating characteristic (ROC) curves were performed.

RESULTS

Over 29 ± 12 mo of follow-up, 46 (10%) patients dead, 156 (33%) showed kidney progression, and 126 (27%) were hospitalized. After multivariate adjustment, 25(OH)D < 20 ng/mL was an independent predictor of all-cause mortality (HR = 2.33; 95%CI: 1.10-4.91; P = 0.027) and kidney progression (HR = 2.46; 95%CI: 1.63-3.71; P < 0.001), whereas the group with 25(OH)D at or above 30 ng/mL did not have a different hazard for outcomes from the reference group. Hospitalization outcomes were predicted by 25(OH) levels (HR = 0.98; 95%CI: 0.96-1.00; P = 0.027) in the unadjusted Cox proportional hazards model, but not after multivariate adjusting. ROC curves identified 25(OH)D levels at highest risk for death, kidney progression, and hospitalization, at 17.4 ng/mL [area under the curve (AUC) = 0.60; 95%CI: 0.52-0.69; P = 0.027], 18.6 ng/mL (AUC = 0.65; 95%CI: 0.60-0.71; P < 0.001), and 19.0 ng/mL (AUC = 0.56; 95%CI: 0.50-0.62; P = 0.048), respectively.

CONCLUSION

25(OH)D < 20 ng/mL was an independent predictor of death and progression in patients with stage 3-5 CKD, with no additional benefits when patients reached the levels at or above 30 ng/mL suggested as optimal by CKD guidelines.