Serum 25-hydroxyvitamin D levels are strongly related to systolic blood pressure but do not predict future hypertension

The relationship between serum 25-hydroxy vitamin D status and hypertension in Syrian population: retrospective cohort study

Introduction

Vitamin D is a liposoluble steroid hormone that plays a crucial role in the maintenance of bone metabolism and calcium homoeostasis. Many studies on the effects of vitamin D on general health have been significantly increased, driven by new findings concerning the systemic and extraskeletal effects of this hormone. This study was performed to determine whether low levels of vitamin D were associated with hypertension in Syrian people.

Materials and methods

This retrospective cohort study consisted of 207 subjects, including 83 (40.1%) patients suffering from essential hypertension and 124 (59.9%) patients with normal blood pressure. Aged older than 18 years, who was referred to the endocrinology clinic from September 2022 to September 2023. The data were analysed by using SPSS (version 25). Logistic regression analyses were performed with adjustments for age, sex, and waist circumference.

Results

Hypertension rates were 73%, 20%, and 5% in 25-hydroxyvitamin D groups less than 12 ng/ml, 12-20 ng/mL, and greater than or equal to 20 ng/ml, respectively. Odds ratios (95% CIs) for hypertension adjusting for age, sex, and waist circumference were 178.6 (30.5_1045.6), 5.13 (0.9_26.5) for 25-hydroxyvitamin D levels less than 12 ng/ml, and 12-20 ng/ml, respectively, compared with the greater than or equal to 20 ng/ml group.

Conclusions

This study has shown a high prevalence of low vitamin D levels (25OHVD/20 ng/ml) among a sample of Syrian people (78.3%). The lowest 25OHVD group was associated with a higher prevalence of hypertension, which refers to an adverse association between vitamin D level and essential hypertension. Further research is needed to confirm this relationship.

The Role of Vitamin D and Its Molecular Bases in Insulin Resistance, Diabetes, Metabolic Syndrome, and Cardiovascular Disease: State of the Art

In the last decade, an increasing awareness was directed to the role of Vitamin D in non-skeletal and preventive roles for chronic diseases. Vitamin D is an essential hormone in regulating calcium/phosphorous balance and in the pathogenesis of inflammation, insulin resistance, and obesity. The main forms of vitamin D, Cholecalciferol (Vitamin D3) and Ergocalciferol (Vitamin D2) are converted into the active form (1,25-dihydroxyvitamin D) thanks to two hydroxylations in the liver, kidney, pancreas, and immune cells. Some anti-inflammatory cytokines are produced at higher levels by vitamin D, while some pro-inflammatory cytokines are released at lower levels. Toll-Like Receptor (TLR) expression is increased, and a pro-inflammatory state is also linked to low levels of vitamin D. Regardless of how it affects inflammation, various pathways suggest that vitamin D directly improves insulin sensitivity and secretion. The level of vitamin D in the body may change the ratio of pro- to anti-inflammatory cytokines, which would impact insulin action, lipid metabolism, and the development and function of adipose tissue. Many studies have demonstrated an inverse relationship between vitamin D concentrations and pro-inflammatory markers, insulin resistance, glucose intolerance, metabolic syndrome, obesity, and cardiovascular disease. It is interesting to note that several long-term studies also revealed an inverse correlation between vitamin D levels and the occurrence of diabetes mellitus. Vitamin D supplementation in people has controversial effects. While some studies demonstrated improvements in insulin sensitivity, glucose, and lipid metabolism, others revealed no significant effect on glycemic homeostasis and inflammation. This review aims to provide insight into the molecular basis of the relationship between vitamin D, insulin resistance, metabolic syndrome, type 1 and 2 diabetes, gestational diabetes, and cardiovascular diseases.

Relationship between serum 25-hydroxyvitamin D concentrations and blood pressure among US adults without a previous diagnosis of hypertension: evidence from NHANES 2005-2018

Background

There are various cross-sectional studies that concluded that vitamin D is associated with blood pressure, but randomized controlled studies have not yielded consistent conclusions. Considering many limitations indeed, our study aimed to examine whether concentrations of 25(OH)D are inversely associated with blood pressure in people without a previous diagnosis of hypertension.

Method

We analyzed data from the 2005-2018 National Health and Nutrition Examination Survey. Odds ratios (ORs) and 95% confidence intervals (CIs) were estimated by applying multivariable logistic regression models. The dose-response relationship was assessed by means of restricted cubic spline regression, and stratification analyses were employed to test the consistency between the subgroups.

Results

Of 17,467 participants aged ≥ 20 years without a previous diagnosis of hypertension, 4,769 had higher blood pressure. Compared with individuals whose 25(OH)D levels were in the bottom quartile (<44.3 nnol/L), adjusting for multiple confounders, the ORs for higher blood pressure were 0.90(95%CI 0.78, 1.05), 0.85(95%CI 0.72, 0.99), and 0.86(95%CI 0.72, 1.02), respectively (P for trend = 0.096). Furthermore, as a continuous variable, 25(OH)D concentrations were non-linearly associated with an increased risk of hypertension (P < 0.001). The interaction between the sleeplessness subgroup and higher blood pressure was significant (P = 0.042).

Conclusion

In adults without a previous diagnosis of hypertension in the United States, concentrations of 25(OH)D were inversely associated with higher blood pressure when it was <84 nmol/L.

Latest Knowledge on the Role of Vitamin D in Hypertension

Hypertension is the third leading cause of the global disease burden, and while populations live longer, adopt more sedentary lifestyles, and become less economically concerned, the prevalence of hypertension is expected to increase. Pathologically elevated blood pressure (BP) is the strongest risk factor for cardiovascular disease (CVD) and related disability, thus making it imperative to treat this disease. Effective standard pharmacological treatments, i.e., diuretics, angiotensin converting enzyme (ACE) inhibitors, angiotensin receptor blocker (ARBs), beta-adrenergic receptor blockers (BARBs), and calcium channel blockers (CCBs), are available. Vitamin D (vitD) is known best for its role in bone and mineral homeostasis. Studies with vitamin D receptor (VDR) knockout mice show an increased renin-angiotensin-aldosterone system (RAAS) activity and increased hypertension, suggesting a key role for vitD as a potential antihypertensive agent. Similar studies in humans displayed ambiguous and mixed results. No direct antihypertensive effect was shown, nor a significant impact on the human RAAS. Interestingly, human studies supplementing vitD with other antihypertensive agents reported more promising results. VitD is considered a safe supplement, proposing its great potential as antihypertensive supplement. The aim of this review is to examine the current knowledge about vitD and its role in the treatment of hypertension.

Circulating 25-hydroxyvitamin D levels and hypertension risk after adjusting for publication bias

BACKGROUND

Previous systematic reviews reported that serum vitamin D deficiency was associated with risk of hypertension. The aim was to conduct a meta-epidemiological analysis for evaluating the potential effects of publication bias.

METHODS

The selection criterion was defined as a follow-up study for evaluating the association between circulating 25-hydroxyvitam D level and hypertension risk in adults. A funnel plot and Egger's test were used to detect a publication bias. If a publication bias was identified, trim-and-fill analysis (TFA) with linear estimator was performed to estimate a summary relative risk (sRR).

RESULTS

The meta-analysis of 13 cohorts resulted in the lower the vitamin D, the higher the risk of hypertension statistically significant (sRR, 1.22; 95% confidence interval [CI], 1.05 to 1.41). But The P-value of Egger's test (=0.015) and asymmetry of the funnel plot showed that there was a publication bias. TFA resulted in that statistical significance disappeared in the association between vitamin D level and hypertension risk in total cohorts (filled sRR, 1.03; 95% CI, 0.89 to 1.18) as well as men and women cohorts.

CONCLUSIONS

The publication bias-adjusted results by TFA had no statistically significant association between vitamin D levels and the risk of hypertension. The significant results in previous systematic reviews might be interpreted as due to publication bias.

Serum Vitamin D Levels in Relation to Hypertension and Pre-hypertension in Adults: A Systematic Review and Dose–Response Meta-Analysis of Epidemiologic Studies

Background

Findings of observational studies that evaluated the association of serum vitamin D status and high blood pressure were contradictory. This meta-analysis of epidemiologic studies assessed the relation of serum vitamin D levels to hypertension (HTN) and pre-hypertension in adults.

Methods

We conducted a systematic search of all published articles up to March 2021, in four electronic databases (MEDLINE (PubMed), Web of Science (ISI), Embase and Scopus), and Google scholar. Seventy epidemiologic studies (10 prospective cohort, one nested case–control, and 59 cross-sectional investigations) that reported relative risks (RRs), odds ratios (ORs), hazard ratios, or prevalence ratios with 95% CIs for HTN or pre-hypertension in relation to serum vitamin D concentrations in adults were included in the analysis.

Results

In prospective studies, a 16% decrease in risk of hypertension was observed in participants with high levels of serum vitamin D compared to low levels (RR: 0.84; 95%CI: 0.73, 0.96; 12 effect sizes). Dose–response analysis in prospective studies revealed that each 25 nmol/L increase in serum vitamin D concentrations resulted in 5% reduced risk of HTN (RR: 0.95; 95% CI: 0.90, 1.00). Also, a significant nonlinear relationship between serum vitamin D levels and HTN was found (P_nonlinearity < 0.001). In cross-sectional investigations, highest vs. lowest level of serum vitamin D was related to reduced odds of HTN (OR: 0.84; 95%CI: 0.79, 0.90; 66 effect sizes) and pre-hypertension (OR: 0.75; 0.95%CI: 0.68, 0.83; 9 effect sizes). Dose–response analysis in these studies showed that each 25 nmol/L increase in serum vitamin D levels was related to a significant 6% reduction in odds of hypertension in all populations (RR: 0.94; 95%CI: 0.90, 0.99) and 3% in studies with representative populations (RR: 0.97; 95%CI: 0.95, 0.99).

Conclusion

This meta-analysis of epidemiologic studies disclosed that serum vitamin D concentrations were inversely related to the risk of HTN in adults, in a dose–response manner in both prospective cohort and cross-sectional studies.

Systematic Review Registration:http://www.crd.york.ac.uk/Prospero, identifier: CRD42021251513.

Vitamin D status is favorably associated with the cardiovascular risk factors in adults with obesity

BACKGROUND & AIMS

Previous investigations have been indicated that vitamin D deficiency is an amendable risk for cardiovascular disease (CVD) in the general populations. Limited data is available concerning the relationship of vitamin D status and risk factors of CVD in the individuals with obesity and the existing data are highly controversial. We investigated whether serum vitamin D situation is related to multiple traditional CVD risk factors in Iranian obese subjects.

METHODS

A cross-sectional study was done among 214 Iranian adults with obesity (94 males and 120 females) aged 20-60 years, who attended the specialized outpatient clinics in Zabol city. Participants were categorized as vitamin D sufficient, insufficient, and deficient according to their serum 25(OH)D concentrations. Afterward, the presence of hypercholesterolemia, hypertriglyceridemia, low high-density lipoprotein cholesterol (HDL-C), high low-density lipoprotein cholesterol (LDL-C) as well as diabetes, hypertension, and high serum concentrations of high-sensitivity C-reactive protein (hs-CRP) as CVD risk factors were evaluated in the participants.

RESULTS

There was a noticeable regular trend regarding hypercholesterolemia (p = 0.008), high LDL-C (p = 0.024), hypertension (p = 0.021), and high hs-CRP (p < 0.0001) across various categories of vitamin D status. In adjusted model, vitamin D-deficient subjects were at higher risk for having hypercholesterolemia (OR: 3.22, p = 0.031), high LDL-C (OR: 2.37, p = 0.047), hypertension (OR: 2.32, p = 0.042), and high hs-CRP (OR: 5.49, p = 0.001) than ones with sufficient vitamin D status.

CONCLUSIONS

Vitamin D deficiency in obese subjects was found to be strongly related to higher risk of unfavorable lipid profile, hypertension, and high hs-CRP.

Vitamin D Deficiency Is a Potential Risk for Blood Pressure Elevation and the Development of Hypertension

Background and objectives: Hypertension is a global health problem and a major risk factor for cardiovascular diseases. Vitamin D deficiency is closely related to high blood pressure and the development of hypertension. This study investigated the relationship between the vitamin D and blood pressure status in healthy adults, and their 8-year follow-up was added. Materials and Methods: A total of 491 healthy middle-aged participants without any chronic illness, ages 21 to 67 at baseline, were divided into two groups as non-optimal blood pressure (NOBP) and optimal blood pressure (OBP). NOBP group was divided into two subgroups: normal (NBP) and high normal blood pressure (HNBP). Serum 25-hydroxy vitamin D levels were measured with the immunoassay method. 8-year follow-up of the participants was added. Results: The average vitamin D level was detected 32.53 ± 31.50 nmol/L in the OBP group and 24.41 ± 14.40 nmol/L in the NOBP group, and a statistically significant difference was found (p < 0.001). In the subgroup analysis, the mean vitamin D level was detected as 24.69 ± 13.74 and 24.28 ± 14.74 nmol/L in NBP and HNBP, respectively. Together with parathyroid hormone, other metabolic parameters were found to be significantly higher in the NOBP. During a median follow-up of 8 years, higher hypertension development rates were seen in NOBP group (p < 0.001). Conclusions: The low levels of vitamin D were significantly associated with NBP and HNBP. The low levels of vitamin D were also associated with the development of hypertension in an 8-year follow-up.

The Interdependency and Co-Regulation of the Vitamin D and Cholesterol Metabolism

Vitamin D and cholesterol metabolism overlap significantly in the pathways that contribute to their biosynthesis. However, our understanding of their independent and co-regulation is limited. Cardiovascular disease is the leading cause of death globally and atherosclerosis, the pathology associated with elevated cholesterol, is the leading cause of cardiovascular disease. It is therefore important to understand vitamin D metabolism as a contributory factor. From the literature, we compile evidence of how these systems interact, relating the understanding of the molecular mechanisms involved to the results from observational studies. We also present the first systems biology pathway map of the joint cholesterol and vitamin D metabolisms made available using the Systems Biology Graphical Notation (SBGN) Markup Language (SBGNML). It is shown that the relationship between vitamin D supplementation, total cholesterol, and LDL-C status, and between latitude, vitamin D, and cholesterol status are consistent with our knowledge of molecular mechanisms. We also highlight the results that cannot be explained with our current knowledge of molecular mechanisms: (i) vitamin D supplementation mitigates the side-effects of statin therapy; (ii) statin therapy does not impact upon vitamin D status; and critically (iii) vitamin D supplementation does not improve cardiovascular outcomes, despite improving cardiovascular risk factors. For (iii), we present a hypothesis, based on observations in the literature, that describes how vitamin D regulates the balance between cellular and plasma cholesterol. Answering these questions will create significant opportunities for advancement in our understanding of cardiovascular health.

An evidence-based appraisal of complementary and alternative medicine strategies for the management of hypertension

: Hypertension is a major risk factor for cardiovascular disease and all-cause mortality. Numerous antihypertensive medications and lifestyle changes have proven effective for the reduction of blood pressure (BP). Over the past few decades, the emergence of complementary and alternative medicine (CAM)-based strategies to lower BP have broadened the therapeutic armamentarium for hypertension. CAM is defined as a group of heterogeneous medical treatments that are used to enhance the effect of standard therapy, or, conversely, are implemented as an alternative to standard practice. The available body of evidence does substantiate the BP-lowering effects of certain CAM-based therapies in individuals with and without established hypertension. Collectively, alternative strategies for BP reduction have undergone less rigorous testing than traditional BP-lowering strategies and the lack of robust clinical data has greatly hampered the broad-scale adoption of CAM therapies into clinical practice. Despite these limitations, CAM-based therapies for the reduction of BP require consideration as they could offer substantial public health benefits given the high prevalence of hypertension in the general population. This article reviews some of the most promising CAM-based therapies for the reduction of BP and cardiovascular outcomes based on the current literature.

Association of serum 25-hydroxyvitamin D levels with primary hypertension: a study from south India

Hypertension is a major risk factor for cardiovascular and cerebrovascular disease. Recent studies have identified an association between low vitamin D levels and hypertension. We investigated the association between vitamin D levels and hypertension in the general population. We recruited 400 hypertensive subjects and compared them with 400 age- and sex-matched normotensive subjects. This study was carried out at Yashoda Hospital, Hyderabad, India from January 2015 to December 2017. Both groups underwent risk factor evaluation, estimation of serum 25-hydroxyvitamin D levels, and C-reactive protein (CRP) and liver function tests. Out of the 400 hypertensive subjects, 164 (40.2%) had serum 25-hydroxyvitamin D deficiency, compared with 111 (27.7%) normotensive subjects (p = 0.0001). Deficiency of serum 25-hydroxyvitamin D in hypertensive subjects was significantly associated with CRP positivity, low levels of mean serum calcium, low levels of mean serum phosphorous, high levels of mean alkaline phosphatase (p < 0.0001), and abnormal alanine transaminase (ALT) (p = 0.0015) compared with the same parameters in the normotensive subjects. After adjustment in the multiple logistic regression analysis, serum 25-hydroxyvitamin D deficiency (odds: 1.78; 95% CI: 1.31-2.41), CRP positivity (odds: 1.48; 95% CI: 1.48-2.32) and abnormal ALT (odds: 1.2; 95% CI: 0.98-1.94) were significantly associated with hypertension. Serum 25-hydroxyvitamin D deficiency was significantly associated with hypertension.

Effect of Vitamin D on Blood Pressure and Hypertension in the General Population: An Update Meta-Analysis of Cohort Studies and Randomized Controlled Trials

Background

The effect of vitamin D supplementation on blood pressure has been explored in previous meta-analyses, but whether the association is causal in the general population is still unknown. We evaluated the association comprehensively and quantitatively.

Methods

We searched PubMed and Embase for relevant cohort studies and randomized controlled trials (RCTs). We used a 2-step generalized least-squares method to assess the dose–response association of circulating 25-hydroxyvitamin D (25[OH]D) and hypertension and a fixed-effects model to pool the weighted mean differences (WMDs) and corresponding 95% confidence intervals (95% CIs) of blood pressure across RCTs.

Results

We identified 11 cohort studies and 27 RCTs, with 43,320 and 3,810 participants, respectively. The dose–response relationship between circulating 25(OH)D levels and hypertension risk was approximately L-shaped (P_nonlinearity = .04), suggesting that the risk of hypertension increased substantially below 75 nmol/L as 25(OH)D decreased, but it remained significant over the range of 75–130 nmol/L. However, pooled results of RCTs showed that there was no significant reduction in systolic blood pressure (WMD, −0.00 mm Hg; 95% CI, −0.71 to 0.71) or diastolic blood pressure (WMD, 0.19 mm Hg; 95% CI, −0.29 to 0.67) after vitamin D intervention.

Conclusions

The results of this meta-analysis indicate that supplementation with vitamin D does not lower blood pressure in the general population. RCTs with long-term interventions and a sufficient number of participants who have low levels of vitamin D are needed to validate these findings.

Association between vitamin D and hypertension in people coming for health check up to a tertiary care centre in South India

INTRODUCTION

Vitamin D has many effects apart from its role in calcium metabolism and bone health. Vitamin D is derived from endogenous ultraviolet-B induced vitamin D synthesis in the skin, and the current high prevalence of vitamin D deficiency in India, can be attributed to lifestyle related low sunlight exposure. Identification of the vitamin D receptor (VDR) in almost all human cells, suggests a role in extra skeletal diseases. Studies have shown that vitamin D deficiency is an independent risk factor for hypertension.

AIM

To evaluate the association between vitamin D and hypertension in people coming for health check up to a tertiary care center in South India.

MATERIALS AND METHODS

Study was carried out as a cross sectional study in a tertiary care hospital in South India. Participants (520) were both males and females (337 males and 183 females), between the age group of 20-60 years attending the comprehensive health check up clinic of our hospital.

STATISTICAL ANALYSIS

Statistical analysis was done using IBM SPSS statistics 20.0.

RESULTS

Severe vitamin D deficiency was highly prevalent in people with hypertension than in people without hypertension (P value <0.001).

CONCLUSION

Since India is a tropical country, till recently it was believed that vitamin D deficiency and its ill effects are uncommon. But it was found that, vitamin D deficiency was highly prevalent in people with hypertension in South India, emphasizing the need of early vitamin D supplementation. Therefore, to reduce cardiovascular morbidity, early identification of vitamin D deficiency and appropriate vitamin D supplementation may be of primary importance in population, especially like ours, having high prevalence.

Sex-specific role of CYP24A1 rs2762939 in the risk of essential hypertension based on the serum vitamin D and total renin concentrations

CYP24A1, Vitamin D 24-hydroxylase catabolizes 25-hydroxyvitamin D (25(OH)D) and 1,25-dihydroxyvitamin D to 24-hydroxylated vitamin D products. It is widely known that low Vitamin D can lead to increased renal renin and angiotensin II production, consequently elevating blood pressure or development of essential hypertension (EH). We have conducted an investigation on hypertensives and controls to evaluate the association of the gene variant, CYP24A1 rs2762939 and 25(OH)D in an Indian population with EH. On gender-based stratification, with multivariate logistic analysis after adjustment for covariates, the CYP24A1 rs2762939 CC variant showed a higher risk of EH in males (aOR = 3.141, CI 1.164-8.478, P = .024) while females illustrated an inverse association with EH (aOR = 0.398, CI 0.172-0.092, P = .031). The 25(OH)D levels among the three genotypes of hypertensives substantiate these results. Our results clearly suggest that gender, CYP24A1 rs2762939, and Vitamin D status may play a significant role in disease susceptibility towards EH in Indian population.

Inverse Relationship between Metabolic Syndrome and 25-Hydroxyvitamin D Concentration in Elderly People without Vitamin D deficiency

Vitamin D status is inversely associated with the prevalence of metabolic syndrome (MetS). Whether this is true in the elderly without vitamin D deficiency is rarely investigated. Our data source is a cross-sectional survey of 1,966 community-dwelling elderly Taiwanese in 2012. An overnight fasting blood were obtained for biochemistry variables. Vitamin D deficiency was defined as serum 25-hydroxyvitamin D3 [25(OH)D] concentration <20 ng/mL. MetS is defined using modified ATP-III criteria. Of 523 participants without vitamin D deficiency (Men/Women = 269/254, age = 76.0 ± 6.2 years old [65–102 years old]), mean 25(OH)D was 44.0 ± 11.1 ng/mL, and the MetS prevalence of MS was 46.5%. Serum 25(OH)D was negatively associated with osteocalcin, the homeostatic model assessment insulin resistance (HOMA-IR) index, body mass index (BMI), and glycated hemoglobin A1c. Participants with more MetS features have lower serum 25(OH)D and osteocalcin. Binary logistic regression models showed that 25(OH)D, physical activity, and osteocalcin were negatively independent MetS factors, but that the HOMA-IR index, BMI, and being female were positively independent factors. The risk of MetS was progressively lower along with the increased 25(OH)D concentration, even above 60 ng/mL. In conclusion, a low 25(OH)D concentration is an independent risk factor for MetS in elderly people without vitamin D deficiency.

Vitamin D supplementation does not improve CVD risk factors in vitamin D-insufficient subjects

OBJECTIVE

Low serum 25(OH)D levels are associated with cardiovascular disease (CVD) and some of its risk factors. However, in interventional studies, the effects of vitamin D supplementation have been uncertain, possibly due to inclusion of vitamin D-sufficient subjects. Our aim was therefore to examine effects of vitamin D supplementation on CVD risk factors in vitamin D-insufficient subjects.

DESIGN

Double-blinded randomized controlled trial.

METHODS

A 4-month interventional study with high-dose vitamin D (100,000 IU loading dose, followed by 20,000 IU/week) or placebo with measurements of blood pressure, lipids (total-, LDL- and HDL-cholesterol, triglycerides, apolipoproteins A1 and B), and glucose metabolism parameters (blood glucose, HbA_1c, serum human receptors for advanced glycation end products (sRAGE), insulin, C-peptide and HOMA-IR).

RESULTS

A total of 422 subjects with mean serum 25(OH)D level 34 nmol/L were included, with 411 subjects completing the study. Serum 25(OH)D levels increased with 56 nmol/L and decreased with 4 nmol/L in the vitamin D and placebo group, respectively. We found no statistically significant differences between the two groups in any of the measured CVD risk factors, except for a minor increase in sRAGE in the vitamin D group. Stratified analyses of subjects with low baseline serum 25(OH)D levels alone, or combined with blood pressure, lipid and HOMA-IR values above the median for the cohort, did not skew the results in favour of vitamin D supplementation.

CONCLUSION

Supplementation with vitamin D in subjects with baseline vitamin D insufficiency does not improve CVD risk factor profile.

Vitamin D Deficiency, Supplementation, and Cardiovascular Health

Vitamin D has been traditionally recognized as a vitamin quintessential for bone-mineral health. In the past 2 decades, numerous experimental and observational studies have highlighted the role of vitamin D in immunity, metabolic syndrome (obesity and diabetes), cancers, renal disease, memory, and neurological dysfunction. In this article, we review important studies that focused on the impact of vitamin D on blood pressure, myocardial infarction, peripheral arterial disease, heart failure, and statin intolerance. Amidst the current pool of ambiguous evidence, we intend to discuss the role of vitamin D in "high-value cardiovascular health care".

RCTS are the only appropriate way to demonstrate the role of vitamin D in health

Despite thousands of vitamin D studies published, including hundreds of reviews and meta-analyses, it is still uncertain if supplementation with vitamin D will have positive health effects, except for the skeleton. This cannot be answered by doing more observational studies as it is impossible to control for confounding factors and reverse causality. The only way to firmly prove positive vitamin D effects is by doing the properly designed randomized controlled trials (RCTs). However, it has been difficult to show the expected positive effects by vitamin D supplementation in RCTs, which may indicate that the effects, if present must be small. On the other hand, results from Mendelian randomization studies have shown promising results at least for mortality and multiple sclerosis. In the near future, results from several large RCTs with hard endpoints will be available. If these show positive results, the main question on vitamin D and health is answered. If they turn out negative, they will be criticized for having included subjects without vitamin D deficiency, and some studies might not have used an optimal dosing regimen. New and better-designed RCTs will then be needed, but will be very hard to perform.

Vitamin D, Calcium, and Cardiovascular Disease: A"D"vantageous or "D"etrimental? An Era of Uncertainty

While the function of vitamin D in regulating calcium homeostasis is well established, there has been growing interest in its role in the prevention of numerous chronic diseases, including cardiovascular disease (CVD). There is mounting epidemiological evidence suggesting that vitamin D deficiency is linked to increased CVD risk. However, the results of previous vitamin D supplementation trials have yielded mixed results in regards to cardiovascular health, and the results of ongoing large-scale randomized controlled trials are not yet available. Further complicating the issue, calcium supplementation, which is often prescribed concurrently with vitamin D, has been associated with increased CVD risk in some (but not all) studies. Thus, it is currently unclear whether vitamin D supplements, particularly for those that are deficient, can help prevent the development of CVD. In addition, there has not been uniform consensus regarding the threshold of 25-hydroxyvitamin D levels that constitutes "sufficiency" across organizational guidelines. This review will provide an update on the most recent evidence regarding the effects of vitamin D and calcium supplements on CVD clinical outcomes, summarize ongoing vitamin D trials, and discuss the current but remarkably disparate recommendations regarding vitamin D deficiency screening and supplementation.

25-hydroxyvitamin D Levels was not Associated with Blood Pressure and Arterial Stiffness in Patients with Chronic Kidney Disease

Background

We investigated the effect of vitamin D deficiency on cardiovascular risk profiles in an Asian population with chronic kidney disease (CKD).

Methods

A total of 210 participants (62 non-dialysis CKD patients and 148 hemodialysis [HD] patients) were enrolled between December 2009 and February 2010. Vitamin D deficiency was determined using the serum 25-hydroxyvitamin D [25(OH)D] concentration. Blood pressure and arterial stiffness were measured. Subjects were divided into groups according to 25(OH)D concentration based on a cut-off of 13.5 ng/mL in non-dialysis CKD patients and 11.3 ng/mL in HD patients.

Results

The mean age was 61.7±12.3 years in non-dialysis CKD patients and 57.0±12.7 years in HD patients. In the non-dialysis CKD group, mean estimated glomerular filtration rate (eGFR) was 29.7±15.4 mL/min/1.73 m². Mean 25(OH)D concentration was 13.6±7.8 ng/mL in non-dialysis CKD patients and 11.3±6.7 ng/mL in HD patients. More than half of the subjects had vitamin D deficiency (67.6% in non-dialysis CKD patients and 80.4% in HD patients). There were no significant differences in systolic blood pressure, pulse pressure, and arterial stiffness between higher and lower 25(OH)D groups among non-dialysis CKD and HD patients. Multivariate analysis revealed that female sex (odds ratio [OR]: 5.890; 95% confidence interval [CI]: 2.597–13.387; p<0.001) and presence of diabetes (OR: 2.434; 95% CI: 1.103–5.370; p=0.028) were significantly associated with lower serum 25(OH)D levels in HD patients.

Conclusion

The prevalence of vitamin D deficiency was high in both nondialysis CKD patients and HD patients. Serum 25(OH)D concentration was not a significant factor associated with blood pressure and arterial stiffness among non-dialysis CKD and HD patients.

Nutraceutical approaches to metabolic syndrome

Metabolic Syndrome (MetS), affecting at least 30% of adults in the Western World, is characterized by three out of five variables, from high triglycerides, to elevated waist circumference and blood pressure. MetS is not characterized by elevated cholesterolemia, but is rather the consequence of a complex interaction of factors generally leading to increased insulin resistance. Drug treatments are of difficult handling, whereas well-characterized nutraceuticals may offer an effective alternative. Among these, functional foods, e.g. plant proteins, have been shown to improve insulin resistance and reduce triglyceride secretion. Pro- and pre-biotics, that are able to modify intestinal microbiome, reduce absorption of specific nutrients and improve the metabolic handling of energy-rich foods. Finally, specific nutraceuticals have proven to be of benefit, in particular, red-yeast rice, berberine, curcumin as well as vitamin D. All these can improve lipid handling by the liver as well as ameliorate insulin resistance. While lifestyle approaches, such as with the Mediterranean diet, may prove to be too complex for the single patient, better knowledge of selected nutraceuticals and more appropriate formulations leading to improved bioavailability will certainly widen the use of these agents, already in large use for the management of these very frequent patient groups. Key messages Functional foods, e.g. plant proteins, improve insulin resistance. Pro- and pre-biotics improve the metabolic handling of energy-rich foods. Nutraceutical can offer a significant help in handling MetS patients being part of lifestyle recommendations.

The association between serum 25-hydroxyvitamin D3 concentration and serum lipids in the rural population of China

Background

Vitamin D deficiency is implicated in some diseases, including cardiovascular. Few studies have assessed the correlation between 25-hydroxyvitamin D3 [25(OH) D3] and serum lipids. In this study, we explored the correlation between serum 25(OH) D3 concentrations and serum lipids with a typical sample of the rural population in China.

Methods

Face-to-face research was used to gather some basic information. Fasting serum concentrations of 25-(OH) D3, total cholesterol (TC), triglyceride (TG), HDL cholesterol (HDL-C) and, LDL cholesterol (LDL-C) tested in the laboratory.

Results

The mean of serum 25(OH) D3 level was 28.71 ± 29.29 ng/mL. The results showed that the dyslipidemia was strongly associated with gender (P = 0.031), drinking (P = 0.043), high-fat diet intake (P = 0.017), HDL-C (P<0), TG (P<0), body mass index (BMI) (P<0) and serum 25(OH)D3 levels (P = 0.002). There was a positive correlation between serum 25(OH)D3 and HDL-C (P<0) in all groups. The relationship between 25(OH) D3 and LDL-C (P = 0.024) was discovered only in normal lipid group. The multivariable adjusted odds ratio (95%CI) of hypoalphalipoproteinemia/HDL and dyslipidemia by comparing the sufficiency vs. the deficiency serum 25-(OH) D3 level were 0.31 (0.192, 0.499) (P = 0.001) and 0.52 (0.36, 0.73) (P = 0.005), respectively.

Conclusions

Serum 25(OH) D3 concentrations were associated with the serum lipids level and the association was different in normal serum lipid group and dyslipidemia group. With the increase of serum 25(OH) D3 levels, the incidence of dyslipidemia decreased.

Vitamin D and Blood Pressure Among U.S. Adults: A Cross-sectional Examination by Race/Ethnicity and Gender

INTRODUCTION

The cross-sectional association of serum vitamin D levels with blood pressure and hypertension status among a representative sample of U.S. adults was examined.

METHODS

Participants of the National Health and Nutrition Examination Survey from 2001 to 2010 were included in these analyses. Harmonizing of the vitamin D levels from 2001 to 2006 with vitamin D measurement from 2007 to 2010 was done using regression equations released by the Centers for Disease Control and Prevention. Use of vitamin D supplements was assessed for all participants. Statistical analyses included examination of linear association of vitamin D levels with blood pressure and non-linear cubic splines with hypertension in overall population, by gender, and by race/ethnicity.

RESULTS

With every 10 nmol/L higher vitamin D, systolic blood pressure decreased by 0.19 mmHg in this population (p<0.01). In fully adjusted stratified analyses, this association was present among females (-0.25 mmHg, p<0.01) and non-Hispanic whites (0.22 mmHg, p<0.01). After race/ethnic and gender stratification, this association was observed among non-Hispanic white females (0.26 mmHg, p=0.01), non-Hispanic black females (0.65 mmHg, p=0.02), and marginally significant among Hispanic males (0.33 mmHg, p=0.07). Non-parametric assessment with cubic splines show that vitamin D has an inverse association with odds of hypertension up to 100 nmol/L with no apparent benefit at higher levels in overall population, and even lower threshold levels of vitamin D in non-Hispanic blacks (50 nmol/L) and Hispanic Americans (70 nmol/L).

CONCLUSIONS

Significant race/ethnic and gender differences exist in the association of vitamin D and systolic blood pressure. Odds for hypertension are reduced significantly at higher vitamin D levels, but this benefit plateaus at very high vitamin D levels.

No effect of vitamin D supplementation on cardiovascular risk factors in subjects with metabolic syndrome: a pilot randomised study

Introduction

Patients with metabolic syndrome (MetS) may have lower 25-hydroxyvitamin D (25(OH)VitD) serum levels compared with non-MetS individuals. Vitamin D (VitD) deficiency is associated with various cardiovascular disease (CVD) risk factors. Yet, the effect of VitD supplementation on MetS remains uncertain. Our aim was to examine the effect of VitD supplementation on CVD risk factors in MetS subjects.

Material and methods

This pilot study had a PROBE (prospective, randomised, open-label, blinded end-point) design. Fifty patients with MetS were included and randomised either to dietary instructions (n = 25) (control group) or dietary instructions plus VitD 2000 IU/day (n = 25) (VitD group) for 3 months. This study is registered in ClinicalTrials.gov (NCT01237769).

Results

In both groups a similar small weight reduction was achieved. In the VitD group serum 25(OH)VitD levels significantly increased by 91% (from 16.0 (3.0–35.0) to 30.6 (8.4–67.0) ng/ml, p < 0.001), while in the control group no significant change was observed (from 10.0 (4.0–39.6) to 13.0 (3.5–37.0) ng/ml). In both groups triglycerides, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, fasting glucose, haemoglobin A_1c, homeostasis model assessment index and diastolic blood pressure did not significantly change. Systolic blood pressure decreased by 3.7% (from 134 ±14 to 129 ±13 mm Hg, p = 0.05) in the VitD group, while it decreased by 1.5% (from 132 ±13 to 130 ±16 mm Hg, p = NS) in the control group (p = NS between groups). In the VitD group serum 25(OH)VitD increase was negatively correlated with SBP decrease (r = –0.398, p = 0.049).

Conclusions

VitD supplementation (2000 IU/day) did not affect various CVD risk factors in patients with MetS.

The Effect of Improved Serum 25-Hydroxyvitamin D Status on Glycemic Control in Diabetic Patients: A Meta-Analysis

BACKGROUND

Type 2 diabetes is a global health concern, with an increased prevalence and high cost of treatment.

OBJECTIVE

The aim of this systematic review and meta-analysis was to determine the effect of vitamin D supplementation and improved vitamin D status on glycemia and insulin resistance in type 2 diabetic patients.

DATA SOURCE

We searched PUBMED/Medline, Cumulative Index to Nursing and Allied Health, and Cochrane Library (until January 2017).

STUDY SELECTION

Prospective clinical trials were selected evaluating the impact of vitamin D supplementation on glycosylated hemoglobin (HbA1c), serum fasting plasma glucose (FPG), and homeostatic model assessment of insulin resistance (HOMA-IR) in diabetic patients.

DATA EXTRACTION AND SYNTHESIS

We used a random-effects model to synthesize quantitative data, followed by a leave-one-out method for sensitivity analysis. The systematic review registration was CRD42017059555. From a total of 844 entries identified via literature search, 24 controlled trials (1528 individuals diagnosed with type 2 diabetes) were included. The meta-analysis indicated a significant reduction in HbA1c [mean difference: -0.30%; 95% confidence interval (CI): -0.45 to -0.15, P < 0.001], FPG [mean difference: -4.9 mg/dL (-0.27 mmol/L); 95% CI: -8.1 to -1.6 (-0.45 to -0.09 mmol/L), P = 0.003], and HOMA-IR (mean difference: -0.66; 95% CI: -1.06 to -0.26, P = 0.001) following vitamin D supplementation and significant increase in serum 25-hydroxyvitamin D levels [overall increase of 17 ± 2.4 ng/mL (42 ± 6 nmol/L)].

CONCLUSIONS

Vitamin D supplementation, a minimum dose of 100 µg/d (4000 IU/d), may significantly reduce serum FPG, HbA1c, and HOMA-IR index, and helps to control glycemic response and improve insulin sensitivity in type 2 diabetic patients.

Non-skeletal health effects of vitamin D supplementation: A systematic review on findings from meta-analyses summarizing trial data

BACKGROUND

A large number of observational studies have reported harmful effects of low 25-hydroxyvitamin D (25OHD) levels on non-skeletal outcomes. We performed a systematic quantitative review on characteristics of randomized clinical trials (RCTs) included in meta-analyses (MAs) on non-skeletal effects of vitamin D supplementation.

METHODS AND FINDINGS

We identified systematic reviews (SR) reporting summary data in terms of MAs of RCTs on selected non-skeletal outcomes. For each outcome, we summarized the results from available SRs and scrutinized included RCTs for a number of predefined characteristics. We identified 54 SRs including data from 210 RCTs. Most MAs as well as the individual RCTs reported null-findings on risk of cardiovascular diseases, type 2 diabetes, weight-loss, and malignant diseases. Beneficial effects of vitamin D supplementation was reported in 1 of 4 MAs on depression, 2 of 9 MAs on blood pressure, 3 of 7 MAs on respiratory tract infections, and 8 of 12 MAs on mortality. Most RCTs have primarily been performed to determine skeletal outcomes, whereas non-skeletal effects have been assessed as secondary outcomes. Only one-third of the RCTs had low level of 25OHD as a criterion for inclusion and a mean baseline 25OHD level below 50 nmol/L was only present in less than half of the analyses.

CONCLUSIONS

Published RCTs have mostly been performed in populations without low 25OHD levels. The fact that most MAs on results from RCTs did not show a beneficial effect does not disprove the hypothesis suggested by observational findings on adverse health outcomes of low 25OHD levels.

Evaluation of the Relationship between Serum 25-Hydroxy Vitamin D and Hypertension in Hamadan, Iran-A Case Control Study

INTRODUCTION

Hypertension or high blood pressure is one of the main reasons of fatality in the world. The role of vitamin D in developing hypertension has not been proved yet. Some studies have shown positive correlation between low serum vitamin D level and hypertension. Due to this fact, recognising hypertension risk factors such as potential impact of low serum vitamin D level seems to be required.

AIM

This study was conducted to evaluate potential impact of serum vitamin D level on hypertension.

MATERIALS AND METHODS

This case-control study had 188 subjects including 55 cases suffering from hypertension and 133 controls with normal blood pressure in Hamadan, Iran. After taking the medical history and physical examination, 5 cc of their blood was taken to measure their serum 25-Hydroxyvitamin D [25(OH)D] level through ELISA test. Data analysis was done by version 16.0 of SPSS software and used independent sample t-test and Chi-square test for related comparisons.

RESULTS

Mean and standard deviation of serum 25(OH)D level in patients suffering from hypertension was 13.10±9.7 ng/ml and in control group was 20.87±10.34 ng/ml. This variance was statistically significant (p<0.001). Mean serum 25(OH)D level in both case and control groups was measured after gender and age stratification. Mean serum 25(OH)D level in cases and controls was 13.12±11.4 ng/ml and 21.38±11.47 ng/ml in males (p=0.016) and 13.10±9.91 ng/ml and 19.19±10.55 ng/ml (p=0.004) in females, respectively. Mean serum 25(OH)D level in under 50-year-old was 10.82±8.73 ng/ml and 20.07±11.17 ng/ml in cases and controls respectively (p<0.001). In over 50-year-old, there was no significant relationship between mean serum 25(OH)D and blood pressure levels (p>0.05).

CONCLUSION

According to this study, reverse relationship between serum 25(OH)D and blood pressure levels was seen.

Does Vitamin D Deficiency Lead to Hypertension?

Hypertension (HTN) or high blood pressure is one of the most chronic and deadliest disorders in the world. There are many risk factors responsible for HTN which include age, race, using tobacco, high salt intake, etc. One of the risk factors we would like to highlight is low vitamin D levels. While there is strong evidence that Vitamin D plays an important role in maintaining bone and muscle health, there has been recent debate regarding its role in hypertension. However, there are many studies that have shown an indirect relation between 25-hydroxyvitamin D serum level and blood pressure. However, we suggest that more studies, especially randomised trials, should be conducted.

The effect of vitamin D supplementation on hypertension in non-CKD populations: A systemic review and meta-analysis

OBJECTIVES

To investigate the vitamin D supplementation on blood pressure control by a systemic review and meta-analysis.

METHODS

Randomized controlled clinical trials were analyzed, which date from eight studies in databases including MEDLINE, EMBASE, Clinical trials, China Integrated Knowledge Resources Database and the Cochrane library.

RESULTS

Total 917 patients from eight randomized controlled trials (RCTs), treatment with vitamin D for more than 3months were analyzed. Meta-analysis showed that vitamin D supplementation slightly reduced the systolic blood pressure (SBP) by 1.964mmHg (95% CI, 0.362-3.566; P=0.016), but not lowered diastolic blood pressure (SMD: -0.087, 95% CI, -0.208-0.033; P=0.155). Subgroup analysis also showed that sBP lowering by vitamin D supplementation was not dose-dependent. Comparison to placebo, there is also no statistical difference in SBP lowering by vitamin D supplementation.

CONCLUSIONS

This meta-analysis indicated that vitamin D is not an antihypertensive agent although it has a moderate SBP lowering effect. More RCTs are required to observe the role of vitamin D plus other antihypertensive drugs in blood pressure control, and define the optimum dose, dosing interval, and type of vitamin D to administer.

Effect of Calcitriol Supplementation on Blood Pressure in Older Adults

Recent studies suggest that vitamin D plays an important role in the control of blood pressure. Unfortunately, because older adults are more likely to have low 25-hydroxyvitamin-D [25(OH)D] levels, this study investigated whether calcitriol supplementation reduces blood pressure in older adults with hypertension. The design was a double-blind placebo-controlled randomized clinical trial with 36 randomly assigned subjects (71.7 ± 10 years). Blood pressure and serum levels of 25(OH)D before and after calcitriol intervention (1,000 IU daily for 6 weeks; n = 22) or placebo (n = 23) for 6 weeks were analyzed. At the end of the study, the calcitriol group presented a significant decrease of systolic blood pressure [20.25 mmHg (p = 0.001)] and diastolic blood pressure [7 mmHg (p = 0.01)], compared with the placebo group. In conclusion, 1,000 IU/day of calcitriol for 6 weeks efficiently reduced systolic and diastolic blood pressure levels in this population of older adults presenting with high blood pressure (Clinical Trial Approbation NCT02047799).

Effect of vitamin D3 supplementation on blood pressure in adults: An updated meta-analysis

BACKGROUND AND AIMS

Previous randomized clinical trials (RCTs) of the effects of vitamin D3 supplementation (VD3S) on blood pressure have generated inconsistent results. We evaluated the effect of VD3S on systolic blood pressure (SBP) and diastolic blood pressure (DBP) in a meta-analysis.

DATA SYNTHESIS

Literature searches of PubMed, Scopus, Ovid, and Google scholar for publications in English were conducted up to April 2015. RCTs that assessed the effect of VD3S on SBP and DBP were selected.

CONCLUSIONS

A total of 30 RCTs with 41 arms including 4744 participants were included. The mean duration of the studies was 5.6 ± 4.0 months, and doses of VD3S varied between 200 and 12,000 IU/day. VD3S had no effect on SBP (-0.68 mmHg, 95%CI: -2.19 to 0.84), and DBP (-0.57 mmHg, 95%CI: -1.36 to 0.22). Subgroup analysis revealed that daily vitamin D3 therapy at a dose of >800 IU/day for <6 months in subjects ≥50 years old reduced both SBP and DBP (p < 0.001). In addition, VD3S showed hypotensive effects in healthy subjects and hypertensive patients, but a hypertensive effect in overweight and obese subjects. However, after excluding overweight and obese subjects, VD3S significantly reduced SBP and DBP. VD3S in combination with calcium supplementation significantly elevated SBP (3.64 mmHg, 95%CI: 3.15-4.13) and DBP (1.71 mmHg, 95%CI: 1.25-2.18). No evidence of publication bias was found. The effects of VD3S on blood pressure depend on dose of supplementation, treatment regimens, trial duration, and population subgroup. Supplementation may be beneficial at daily doses >800 IU/day for <6 months in subjects ≥50 years old.

Determinants of vitamin D status in young adults: influence of lifestyle, sociodemographic and anthropometric factors

BACKGROUND

Very few studies have investigated the determinants of circulating 25-hydroxyvitamin D (25[OH]D) in young adults (18-25 years old) using a set of variables that include lifestyle, sociodemographic, and anthropometric data. Our aim was to investigate the association between these variables and vitamin D status in a sample of untreated young adults.

METHODS

A total of 738 young adults were enrolled in a (June cross-sectional study 2012 to May 2014) and were recruited from educational institutions in the Copenhagen area. For multivariate logistic regression subjects was categorized based on 25[OH]D in serum into; vitamin D sufficiency (S-25[OH]D > 50 nmol/L), vitamin D insufficiency (25 nmol/L ≤ S-25[OH]D ≤ 50 nmol/L), vitamin D deficiency (S-25[OH]D < 25 nmol/L). Information on lifestyle factors and education was obtained by self-reported questionnaires.

RESULTS

700 subjects with a valid measurement of S-25[OH]D and a completed questionnaire was analysed. 238 had vitamin D insufficiency, 135 had vitamin D deficiency of which 13 had severe vitamin D deficiency (S-25[OH]D < 12.5 nmol/L). The relative risk (RR) for vitamin D deficiency was highest for men 2.09 (1.52, 2.87); obese subjects 2.00 (1.27, 3.15); smokers 1.33 (1.02, 1.73); subjects who exercised 0-½ hours a week 1.88 (1.21, 2.94); and subjects who consumed fast food once a week 1.59 (1.05, 2.43). The relative risk was significantly lower for subjects who were studying for a Bachelor's degree (0.40 (0.23, 0.68). For vitamin D insufficiency, the highest RR was again for men 1.31 (1.06, 1.61); obese subjects 1.57 (1.17, 2.11); and subjects who exercised 0-½ hours a week 1.51 (1.11, 2.06).

CONCLUSION

In this study of young adults, vitamin D deficiency was highly prevalent. Modifiable factors such as smoking, maintenance of normal BMI, and physical activity are all potential targets for interventional trials to determine the causal order; such knowledge would be useful in improving S-25[OH]D in young adults. The small group with severe vitamin D deficiency warrants increased attention.

Effects of vitamin D binding protein phenotypes and vitamin D supplementation on serum total 25(OH)D and directly measured free 25(OH)D

OBJECTIVE

To determine the relationship between serum total 25-hydroxyvitamin D (25(OH)D), directly measured free 25(OH)D and calculated free 25(OH)D with regard to vitamin D-binding protein (DBP) phenotypes, sex, BMI, age and season, and their interrelationship to vitamin D supplementation.

DESIGN, PATIENTS AND INTERVENTIONS

A randomized controlled trial with 20 000 IU of vitamin D3 per week or placebo for 12 months was designed. A total of 472 subjects, 236 in each of the intervention groups, were included in the analyses.

MAIN OUTCOME MEASURES

Baseline serum concentrations and increases in serum total 25(OH)D, directly measured free 25(OH)D, calculated free 25(OH)D and DBP.

RESULTS

Serum total 25(OH)D and DBP concentrations were significantly lower in subjects with the phenotype Gc2/Gc2 compared to phenotypes with the Gc1S allele, and lower in males compared to females. When using directly measured free 25(OH)D, the differences related to DBP phenotypes and sexes were clearly diminished. All calculated free 25(OH)D concentrations were overestimated compared to the directly measured free 25(OH)D. Serum parathyroid hormone showed an inverse correlation with all vitamin D parameters analyzed. The increases after 12 months of vitamin D supplementation were not significantly different for any of the vitamin D parameters regardless of DBP phenotype, sex or age. Supplementation with vitamin D did not affect serum DBP.

CONCLUSION

Direct measurements of free 25(OH)D reduce the differences seen in total 25(OH)D between DBP phenotype groups and sexes, probably caused by differences in DBP concentrations. With conditions affecting serum DBP concentrations, direct measurements of free 25(OH)D should be considered.

Interaction effect of serum 25-hydroxyvitamin D levels and CYP1A1, CYP1B1 polymorphisms on blood pressure in an elderly population

OBJECTIVE

Hypertension and vitamin D deficiency are prevalent worldwide, especially in the elderly. Considering the possibility of gene-environment contributions to disease development, we evaluated the influence of certain cytochrome P450 polymorphisms and vitamin D levels on blood pressure (BP).

METHODS

We measured serum 25-hydroxyvitamin D levels [25(OH)D] and BP in 535 individuals over 60 years old and identified single-nucleotide polymorphisms (SNPs) of CYP1A1 and CYP1B1 in lymphocyte DNA. Repeated measure analyses were used to determine the statistical association.

RESULTS

The relationship between 25(OH)D and SBP or DBP was inversely significant, and influence of several CYP1A1 and CYP1B1 SNPs on BP was found across different genotypes. Estimated effect of 25(OH)D levels on BP in the group with higher risky genotype scores of selected SNPs (rs4646421, rs2551188, and rs1056836) was greater (β = -2.841, P = 0.004 for SBP; β = -2.035, P = 0.001 for DBP) than the group with lower genotype score (β = -0.878, P = 0.347 for SBP; β = 0.037, P = 0.947 for DBP), and synergistic interaction between vitamin D levels and genotype variations was observed (P-interaction = 0.081 for SBP and 0.008 for DBP). When stratified by the hypertension medication status, interaction effect was found only in individuals taking medication (P-interaction = 0.004 for SBP and 0.001 for DBP).

CONCLUSION

Genetic variations in CYP1A1 and CYP1B1 and the serum levels of 25(OH)D showed synergistic effect on BP, especially in individuals currently in treatment for hypertension.

Association of Serum 25-Hydroxyvitamin D and Parathyroid Hormone With Hypertension in Middle-Aged and Older Korean Adults

BACKGROUND

Previous studies have suggested that serum 25-hydroxyvitamin D [25(OH)D] and parathyroid hormone (PTH) levels are associated with hypertension. However, the associations have yet to be studied in Koreans. This study explored the relationship among serum 25(OH)D, PTH concentrations, and the presence of hypertension in middle-aged and older Korean adults using the most recent nationally representative survey data.

METHODS

A population-based, cross-sectional study was conducted with data collected from 5,260 Korean adults (aged ≥50 years) who participated in the 2010 and 2011 Korean National Health and Nutrition Examination Surveys. Hypertension was defined as a systolic blood pressure ≥140 mm Hg, diastolic blood pressure ≥90 mm Hg, or current use of antihypertensive medication.

RESULTS

The prevalence of hypertension significantly increased according to the quartiles of serum PTH levels (P < 0.0001), but not of serum 25(OH)D levels. In multivariable logistic analysis, the adjusted odds ratios (ORs) for hypertension were significantly higher among participants in the highest quartile than among those in the lowest quartile of serum PTH level, after adjusting for potential confounders (OR = 1.26, 95% confidence interval: 1.02-1.56, P = 0.03). The adjusted ORs for hypertension tended to decrease across the quartiles of serum 25(OH)D level, but the associations were not significant.

CONCLUSION

Serum 25(OH)D was not associated with the presence of hypertension, whereas serum PTH was positively associated, suggesting that serum PTH may be an independent risk factor for hypertension in middle-aged and older Korean adults.

Vitamin D deficiency and essential hypertension

Essential hypertension (EH) results when the balance between vasoconstriction and vasodilation is shifted in favor of vasoconstriction. This balance is controlled by the interaction of genetic and epigenetic factors. When there is an unstable balance, vitamin D deficiency as an epigenetic factor triggers a shift to the side of vasoconstriction. In this article, we critically analyze clinical findings on the effect of vitamin D on blood pressure, combined with progress in molecular mechanisms. We find that vitamin D repletion exerts a clinically significant antihypertensive effect in vitamin D-deficient EH patients. Of note, a few trials reported no antihypertensive effect from vitamin D due to suboptimal study design. Short-term vitamin D supplementation has no effect on blood pressure in normotensive subjects. This could explain the mixed results and may provide a theoretical basis for future trials to identify beneficial effects of vitamin D in intervention for EH.

Metabolic syndrome: A review of the role of vitamin D in mediating susceptibility and outcome

Despite the well-recognised role of vitamin D in a wide range of physiological processes, hypovitaminosis is common worldwide (prevalence 30%-50%) presumably arising from inadequate exposure to ultraviolet radiation and insufficient consumption. While generally not at the very low levels associated with rickets, hypovitaminosis D has been implicated in various very different, pathophysiological processes. These include putative effects on the pathogenesis of neoplastic change, inflammatory and demyelinating conditions, cardiovascular disease (CVD) and diabetes. This review focuses on the association between hypovitaminosis D and the metabolic syndrome as well as its component characteristics which are central obesity, glucose homeostasis, insulin resistance, hypertension and atherogenic dyslipidaemia. We also consider the effects of hypovitaminosis D on outcomes associated with the metabolic syndrome such as CVD, diabetes and non-alcoholic fatty liver disease. We structure this review into 3 distinct sections; the metabolic syndrome, vitamin D biochemistry and the putative association between hypovitaminosis D, the metabolic syndrome and cardiovascular risk.

Vitamin D status and hypertension: a review

Vitamin D is a steroid prohormone synthesized in the skin following ultraviolet exposure and also achieved through supplemental or dietary intake. While there is strong evidence for its role in maintaining bone and muscle health, there has been recent debate regarding the role of vitamin D deficiency in hypertension based on conflicting epidemiological evidence. Thus, we conducted a scoping systematic literature review and meta-analysis of all observational studies published up to early 2014 in order to map trends in the evidence of this association. Mixed-effect meta-analysis was performed to pool risk estimates from ten prospective studies (n=58,262) (pooled risk for incident hypertension, relative risk [RR] =0.76 (0.63–0.90) for top vs bottom category of 25-hydroxyvitamin D [25OHD]) and from 19 cross-sectional studies (n=90,535) (odds ratio [OR] =0.79 (0.73–0.87)). Findings suggest that the better the assessed quality of the respective study design, the stronger the relationship between higher 25OHD levels and hypertension risk (RR =0.67 (0.51–0.88); OR =0.77 (0.72–0.89)). There was significant heterogeneity among the findings for both prospective and cross-sectional studies, but no evidence of publication bias was shown. There was no increased risk of hypertension when the participants were of older age or when they were vitamin D deficient. Younger females showed strong associations between high 25OHD levels and hypertension risk, especially in prospective studies (RR =0.36 (0.18–0.72); OR =0.62 (0.44–0.87)). Despite the accumulating evidence of a consistent link between vitamin D and blood pressure, these data are observational, so questions still remain in relation to the causality of this relationship. Further studies either combining existing raw data from available cohort studies or conducting further Mendelian analyses are needed to determine whether this represents a causal association. Large randomized controlled trials are also needed to determine whether vitamin supplementation may be beneficial in the prevention or the treatment of hypertension.

Vitamin D and health: the need for more randomized controlled trials

The importance of vitamin D for calcium absorption and bone health is undisputed. In addition, vitamin D may also be important for more than the skeleton as low serum levels of 25-hydroxyvitamin D (25(OH)D) have been associated with a number of diseases like cardiovascular disease, diabetes, cancer and infections. This is mainly based on observational studies and proof of causal relations from randomized controlled trials (RCTs) are lacking. At present several large RCTs including from 2152 to 25,000 subjects and with cardiovascular disease and cancer as endpoints are ongoing. Results are expected within 3-5 years, and hopefully these studies will give us a definite answer on need for vitamin D supplementation. However, since vitamin D deficiency (serum 25(OH)D <50nmol/L) has not been an inclusion criterion in these studies, there is a risk of a null effect. If so, one has to establish the effects of vitamin D in truly vitamin D deficient subjects, studies that in retrospect obviously should have been the starting point for RCTs on vitamin D and health. This article is part of a Special Issue entitled '17th Vitamin D Workshop'.

Vitamin D deficiency in the pathogenesis of hypertension: still an unsettled question

Vitamin D deficiency is inversely associated with blood pressure and is felt to contribute to the genesis and maintenance of hypertension. Although well demonstrated in animal studies, in many clinical studies the association between vitamin D status and blood pressure has not been consistently observed or else has been quite small. These discrepancies may relate in part to methodological differences including: patient selection, study size and duration, and, in the case of vitamin D repletion studies, differences in the vitamin D supplement used, its dose, and dosing intervals. Polymorphisms in genes regulating vitamin D activation and function may explain some of the observed inconsistencies as suggested by recent studies. The present review examines experimental and clinical studies bearing on the inverse association between blood pressure and vitamin D status and concludes that a new definition of vitamin D deficiency using additional biomarkers may better select patients with hypertension who will respond to vitamin D supplementation.

Vitamin D depletion aggravates hypertension and target-organ damage

Background

We tested the controversial hypothesis that vitamin D depletion aggravates hypertension and target‐organ damage by influencing renin.

Methods and Results

Four‐week‐old double‐transgenic rats (dTGR) with excess angiotensin (Ang) II production due to overexpression of the human renin (hREN) and angiotensinogen (hAGT) genes received vitamin D‐depleted (n=18) or standard chow (n=15) for 3 weeks. The depleted group had very low serum 25‐hydroxyvitamin D levels (mean±SEM; 3.8±0.29 versus 40.6±1.19 nmol/L) and had higher mean systolic BP at week 5 (158±3.5 versus 134.6±3.7 mm Hg, P<0.001), week 6 (176.6±3.3 versus 162.3±3.8 mm Hg, P<0.01), and week 7 (171.6±5.1 versus 155.9±4.3 mm Hg, P<0.05). Vitamin D depletion led to increased relative heart weights and increased serum creatinine concentrations. Furthermore, the mRNAs of natriuretic peptides, neutrophil gelatinase‐associated lipocalin, hREN, and rRen were increased by vitamin D depletion. Regulatory T cells in the spleen and in the circulation were not affected. Ang metabolites, including Ang II and the counter‐regulatory breakdown product Ang 1 to 7, were significantly up‐regulated in the vitamin D‐depleted groups, while ACE‐1 and ACE‐2 activities were not affected.

Conclusions

Short‐term severe vitamin D depletion aggravated hypertension and target‐organ damage in dTGR. Our data suggest that even short‐term severe vitamin D deficiency may directly promote hypertension and impacts on renin‐angiotensin system components that could contribute to target‐organ damage. The findings add to the evidence that vitamin D deficiency could also affect human hypertension.

Potential pathophysiological role for the vitamin D deficiency in essential hypertension

Vitamin D deficiency has been indicated as a pandemic emerging public health problem. In addition to the well-known role on calcium-phosphorus homeostasis in the bone, vitamin D-mediated processes have been recently investigated on other diseases, such as infections, cancer and cardiovascular diseases. Recently, both the discovery of paracrine actions of vitamin D (recognized as “local vitamin D system”) and the link of vitamin D with renin-angiotensin-aldosterone system and the fibroblast growth factor 23/klotho pathways highlighted its active cardiovascular activity. Focusing on hypertension, this review summarizes the more recent experimental evidence involving the vitamin D system and deficiency in the cardiovascular pathophysiology. In particular, we updated the vascular synthesis/catabolism of vitamin D and its complex interactions between the various endocrine networks involved in the regulation of blood pressure in humans. On the other hand, the conflicting results emerged from the comparison between observational and interventional studies emphasize the fragmentary nature of our knowledge in the field of vitamin D and hypertension, strongly suggesting the need of further researches in this field.

25-Hydroxyvitamin D: analysis and clinical application

25-Hydroxyvitamin D (25-OHD) is one of the most popular tests requested by clinicians nowadays because in addition to bone diseases, many non-skeletal disorders have been suggested to be linked to vitamin D deficiency or insufficiency. Methodologies used in clinical laboratories include competitive vitamin D protein binding assays (CPBA), immunoassays, high performance liquid chromatography (HPLC), and liquid chromatography-tandem mass spectrometry (LC-MS/MS). In this review article, we introduce the basic metabolism and physiology of vitamin D, key issues in the methods for 25-OHD measurement currently used in most clinical laboratories, and clinical applications of 25-OHD testing. We conclude that although the methodologies for 25-OHD testing have improved significantly, considerable bias between different methods and laboratories still exists. Therefore, standardization of the method is critical. The optimal 25-OHD levels should be determined based on the standardized method. Also, more studies are needed to further determine the relationship between vitamin D deficiency or insufficiency and non-skeletal diseases as well as daily vitamin D dose requirement for reducing the risk of non-skeletal diseases.

Association between vitamin D status and risk of metabolic syndrome among Korean postmenopausal women

This study aimed to investigate the association between serum levels of 25-hydroxyvitamin D [25(OH)D] and metabolic syndrome along with its associated risk factors in Korean postmenopausal women. This study was performed using data from the KNHANES 2008–2010 study and included 4,364 postmenopausal Korean women. Clinical and other objective characteristics, seasonality, and presence of metabolic syndrome with its five components were evaluated and correlated with the serum levels of 25(OH)D. Although no statistically significant associations were observed between the levels of serum 25(OH)D and the prevalence of metabolic syndrome, the adjusted OR for elevated blood pressure, elevated triglycerides (TGs), and reduced high-density lipoprotein cholesterol (HDL-C) showed tendency to decrease sequentially as tertiles of serum 25(OH)D levels increased (p for trends  = 0.066, 0.043, and 0.010, respectively). Women in the highest tertile of serum 25(OH)D showed a significant decrease in the prevalence of elevated blood pressure, elevated TGs, and reduced HDL-C as compared with those in the lowest tertile of serum 25(OH)D (p = 0.020, 0.014, and 0.002, respectively). Based on these results, we consider that adequate serum levels of 25(OH)D in Korean postmenopausal women may not entirely indicate a lower risk of developing metabolic syndrome. However, adequate serum levels of 25(OH)D are significantly associated with a decrease in elevated blood pressure, elevated TGs, and reduced HDL-C levels in postmenopausal women.

Vitamin D and the cardiovascular system: an overview of the recent literature

Since the discovery that the enzyme catalyzing the synthesis of the most active natural vitamin D metabolite(calcitriol) and the vitamin D-specific receptor (VDR)were expressed in a wide range of tissues and organs, not only involved in the mineral metabolism (MM), there has been increasing interest on the putative ‘non classical’ roles of vitamin D metabolites, particularly on their possible effects on the cardiovascular (CV) system. These hypothetical CV effects of vitamin D gained particular interesting the nephrology field, given the high prevalence of CV disease in patients affected by either acute or chronic kidney diseases. However, notwithstanding a huge amount of experimental data suggesting a possible protective role of vitamin D on the CV system, the conclusions of two recent meta-analyses from the Cochrane group and a recent statement from the Institute of Medicine, based on a complete revision of the available data, concluded that there is no clear evidence for a role of vitamin D other than that strictly associated with bone health. However, a continuous and increasing flow of new studies still continues to add information on this topic. In the present review, we have tried to critically address the data added on this topicin the last 2 years, considering separately the experimental,observational, and intervention studies that have appeared in PubMed in the last 2 years, discussing the data providing proof, pro or contra, the involvement of vitamin D in CV disease, both in the absence or presence of kidney function impairment.