The association of plasma resistin with dietary sodium manipulation, the renin-angiotensin-aldosterone system, and 25-hydroxyvitamin D3 in human hypertension

Physical Activity and the Acute Hemodynamic Response to ACE Inhibition in Hypertension

Introduction. Physical activity (PA) can reduce blood pressure (BP) in hypertensives through possibly interacting with the renin-angiotensin-aldosterone system (RAAS). We conducted a nested-cohort analysis to determine if self-reported PA was associated with BP responsiveness to acute angiotensin converting enzyme inhibition (ACEi). Methods. Data were extracted from the HyperPATH dataset, a cohort designed to identify mechanisms of cardiometabolic risk. Hypertensives that completed a self-assessed PA questionnaire, hormonal assessments (aldosterone [ALDO]), and BP to a single dose of an ACEi (captopril, 25 mg) were included. All participants (n = 144) were studied on a controlled diet for 7 days. PA was recorded as no PA, or little, moderate, or high amounts of exercise. Analyses were adjusted for age, sex, race, and body mass index. Results. Individuals who reported high amounts of PA displayed a greater BP lowering effect from ACEi compared to those who reported moderate (−14.8 ± 8.1 vs −8.4 ± 9.9 mm Hg, P < .01) or no additional PA (−14.8 ± 8.1 vs −2.6 ± 9.9 mm Hg, P < .001). Exploratory analyses indicated high amounts of PA were associated with a reduced heart rate (54 ± 8 vs 66 ± 10 bpm, P < .001) and blunted ALDO (β = 0.44, 95% confidence interval = 0.19-0.70). Conclusions. Higher self-reported PA was associated with an augmented BP lowering effect to acute ACEi in hypertensive patients.

The Association between Serum Resistin Level, Resistin (-420C/G) Single Nucleotide Variant, and Markers of Endothelial Dysfunction, including Salt Taste Preference in Hypertensive Patients

Background: Resistin action links to conditions such as diabetes, obesity, but its role in hypertension is less well understood. This study aimed to estimate the relationship between resistin (−420G/C) single nucleotide variant (SNV) and markers associated with endothelial dysfunction in hypertension. Methods: The study enrolled 162 hypertensive patients (HT) and 165 non-hypertensive (NHT) patients. Resistin serum concentration was estimated with immuoenzymatic assay. Anthropometric measurements, blood pressure and arterial stiffness index (SI), uric acid (UA) serum concentration, and salty taste preference of normal (NS) or high (HS) were assessed in the study. Genotyping was achieved by polymerase chain reaction-restriction fragment length polymorphism. Results: Resistin concentration and SI do not differ significantly between HT and NHT individuals; UA significantly increased in HT subjects. Resistin, UA, and SI did not differ among particular resistin genotypes in HT, NHT, NS, or HS groups. GG and CG genotypes were more frequent (OR 1.57 (95% CI; 1.01–2.43); p = 0.04) in hypertensive individuals than the NHT group, but less frequent (OR 0.58 (95% CI; 0.37–0.91); p = 0.01) in HS patients compared to NS individuals. Concerning HT patients with different salt preferences, GG + CG genotypes were less frequent (OR 0.50 (95% CI; 0.26–0.97); p = 0.04) in the HS group than in NS individuals. HT carriers of GG and CG genotype have significantly increased UA concentrations compared to the respective NHT subjects. HS individuals carrying GG and CG genotypes have higher SI values than the NS group. Allele G of SNV (−420G/C) adjusted for age, BMI, serum resistin, UA concentration, salt taste preference, SI, and HR values increased the risk of developing hypertensive phenotype 1.8 fold. Conclusions: Resistin SNV (−420G/C) is related to several markers associated with endothelial dysfunction, including salt taste preference in hypertensive patients.

Proteomic and Mechanistic Analysis of Spironolactone in Patients at Risk for HF

OBJECTIVES

This study sought to further understand the mechanisms underlying effect of spironolactone and assessed its impact on multiple plasma protein biomarkers and their respective underlying biologic pathways.

BACKGROUND

In addition to their beneficial effects in established heart failure (HF), mineralocorticoid receptor antagonists may act upstream on mechanisms, preventing incident HF. In people at risk for developing HF, the HOMAGE (Heart OMics in AGEing) trial showed that spironolactone treatment could provide antifibrotic and antiremodeling effects, potentially slowing the progression to HF.

METHODS

Baseline, 1-month, and 9-month (or last visit) plasma samples of HOMAGE participants were measured for protein biomarkers (n = 276) by using Olink Proseek-Multiplex cardiovascular and inflammation panels (Olink, Uppsala, Sweden). The effect of spironolactone on biomarkers was assessed by analysis of covariance and explored by knowledge-based network analysis.

RESULTS

A total of 527 participants were enrolled; 265 were randomized to spironolactone (25 to 50 mg/day) and 262 to standard care ("control"). The median (interquartile range) age was 73 years (69 to 79 years), and 26% were female. Spironolactone reduced biomarkers of collagen metabolism (e.g., COL1A1, MMP-2); brain natriuretic peptide; and biomarkers related to metabolic processes (e.g., PAPPA), inflammation, and thrombosis (e.g., IL17A, VEGF, and urokinase). Spironolactone increased biomarkers that reflect the blockade of the mineralocorticoid receptor (e.g., renin) and increased the levels of adipokines involved in the anti-inflammatory response (e.g., RARRES2) and biomarkers of hemostasis maintenance (e.g., tPA, UPAR), myelosuppressive activity (e.g., CCL16), insulin suppression (e.g., RETN), and inflammatory regulation (e.g., IL-12B).

CONCLUSIONS

Proteomic analyses suggest that spironolactone exerts pleiotropic effects including reduction in fibrosis, inflammation, thrombosis, congestion, and vascular function improvement, all of which may mediate cardiovascular protective effects, potentially slowing progression toward heart failure. (HOMAGE [Bioprofiling Response to Mineralocorticoid Receptor Antagonists for the Prevention of Heart Failure]; NCT02556450).

Association Between Vitamin D and Resistin in Postmenopausal Females With Altered Bone Health

BACKGROUND

Resistin is a relatively novel adipokine that has a role in bone remodeling and may regulate bone mineral density (BMD). Vitamin D and adipokines have a dynamic role in the body's various metabolic processes, including bone metabolism, and may alter bone metabolism in relation to each other. This study aimed to investigate the association between vitamin D and serum resistin levels in postmenopausal non-osteoporotic and osteoporotic females.

METHODS

This correlational analytical study was conducted on 161 postmenopausal females, divided into two groups, non-osteoporotic and osteoporotic, between 50-70 years. Bone mineral density (BMD) was assessed by dual-energy X-ray absorptiometry (DXA) scan. Serum resistin and vitamin D levels were analyzed by enzyme-linked immunosorbent assay (ELISA) method. Serum calcium, phosphate, and alkaline phosphatase with spectrophotometry. A correlation was checked using spearman's rho correlation coefficient, and multivariate stepwise regression analysis was used to predict serum resistin levels.

RESULTS

Postmenopausal females (n=161) having sufficient, insufficient and deficient levels of vitamin D were 87 (54.0%), 64 (39.8%), and 10 (6.2%), respectively. Lumbar spine BMD (p < 0.001), total hip BMD (p < 0.001), and serum resistin levels (p < 0.001) were significantly different between the two groups. There was a significant negative correlation between serum resistin and vitamin D in postmenopausal females (rho = -0.182, p = 0.021) and osteoporotic group (rho = -0.253, p = 0.019) but non-significant in non-osteoporotic group (rho = -0.077, p = 0.509). Serum vitamin D was found to be independent predictor of serum resistin levels, accounting for only 3% variance.

CONCLUSION

Serum vitamin D levels were low while serum resistin levels were high in postmenopausal osteoporotic females and vitamin D is a negative predictor of serum resistin levels.

Serum vitamin D and diabetic foot complications

Background: Foot complications such as ulceration and neuropathy are common complications of diabetes mellitus (DM). Previous reports have demonstrated a possible increased risk of these complications in diabetic patients with low levels of serum vitamin D.Objectctive: The purpose of this study is to compare serum vitamin D levels in diabetic patients with and without Charcot neuroarthropathy (CN), peripheral arterial disease (PAD), infection (DFI), ulceration (DFU), and peripheral neuropathy (DPN). Design: A retrospective chart review of all patients undergoing foot and ankle surgery with a history of DM over a 13 month period was performed. From this cohort, fifty subjects with CN were matched with 50 without CN and preoperative lab values were compared. A secondary evaluation was performed on the subjects' other comorbidities including PAD, DFI, DFU, and DPN. Results: Seventy-eight percent of our patients had vitamin D deficiency or insufficiency. Preoperative serum vitamin D levels were not significantly different between diabetic patients with and without CN (p = 0.55). Diabetic patients with PAD (p = 0.03), DFI (p = 0.0006), and DFU (p = 0.04) were all found to have significantly lower serum vitamin D levels than diabetic patients without these complications. Lower levels of serum albumin and higher serum creatinine were also noted with subjects with PAD, DFI, DPN, and DFU. While seasonal serum vitamin D level fluctuation was noted, this difference did not reach statistical significance with the numbers available. Conclusion: We found various lower extremity complications to be associated with low serum vitamin D including PAD, DFI, and DFU. While other studies have questioned the role of vitamin D and CN, we were unable to identify any significant difference between diabetic patients with and without Charcot neuroarthropathy. Level of evidence: Level 2.

Vitamin D supplementation increases adipokine concentrations in overweight or obese adults

PURPOSE

Vitamin D regulates adipokine production in vitro; however, clinical trials have been inconclusive. We conducted secondary analyses of a randomized controlled trial to examine whether vitamin D supplementation improves adipokine concentrations in overweight/obese and vitamin D-deficient adults.

METHODS

Sixty-five individuals with a BMI ≥ 25 kg/m² and 25-hydroxyvitamin D (25(OH)D) ≤ 50 nmol/L were randomized to oral cholecalciferol (100,000 IU single bolus followed by 4,000 IU daily) or matching placebo for 16 weeks. We measured BMI, waist-to-hip ratio, % body fat (dual X-ray absorptiometry), serum 25(OH)D (chemiluminescent immunoassay) and total adiponectin, leptin, resistin, and adipsin concentrations (multiplex assay; flow cytometry). Sun exposure, physical activity, and diet were assessed using questionnaires.

RESULTS

Fifty-four participants completed the study (35M/19F; mean age = 31.9 ± 8.5 years; BMI = 30.9 ± 4.4 kg/m²). After 16 weeks, vitamin D supplementation increased 25(OH)D concentrations compared with placebo (57.0 ± 21.3 versus 1.9 ± 15.1 nmol/L, p < 0.001). There were no differences between groups for changes in adiponectin, leptin, resistin, or adipsin in unadjusted analyses (all p > 0.05). After adjustment for baseline values, season, sun exposure, and dietary vitamin D intake, there was a greater increase in adiponectin (β[95%CI] = 13.7[2.0, 25.5], p = 0.02) and leptin (β[95%CI] = 22.3[3.8, 40.9], p = 0.02) in the vitamin D group compared with placebo. Results remained significant after additional adjustment for age, sex, and % body fat (p < 0.02).

CONCLUSIONS

Vitamin D may increase adiponectin and leptin concentrations in overweight/obese and vitamin D-deficient adults. Further studies are needed to clarify the molecular interactions between vitamin D and adipokines and the clinical implications of these interactions in the context of obesity.

CLINICAL TRIAL REGISTRATION

clinicaltrials.gov: NCT02112721.

Serum adipokines and vitamin D levels in patients with type 1 diabetes mellitus

INTRODUCTION

Adiponectin, leptin and resistin are adipokines that play important roles in the regulation of lipid and carbohydrate metabolism in type 2 diabetes (T2DM). However, their influence in type 1 diabetes mellitus is still unknown. The aim of this study was to measure serum adiponectin, leptin and resistin levels and to investigate their relationships with vitamin D and other clinical and laboratory parameters in patients with type 1 diabetes.

MATERIAL AND METHODS

Fifty subjects with type 1 diabetes and 50 healthy age- and sex-matched subjects were selected from the Endocrinology Outpatient Clinic of Cairo University Pediatrics Hospital. Enzyme-linked immunosorbent assay was used to measure the levels of leptin, adiponectin and resistin. Vitamin D levels were measured using electro-chemiluminescence immunoassay.

RESULTS

There were no significant differences in adiponectin and leptin levels between diabetic and control subjects (p = 0.6 and p = 0.5 respectively). Resistin levels were significantly higher in the diabetic group compared to controls (p < 0.001) and in postpubertal patients compared to prepubertal patients (p < 0.04). Serum resistin in type 1 diabetes showed a negative correlation with vitamin D (p < 0.001) and a positive correlation with glycated hemoglobin (HbA_1c) (p = 0.006), while other adipokines were not interrelated.

CONCLUSIONS

These results strongly support a role of resistin and vitamin D deficiency in the pathophysiology of type 1 diabetes. Vitamin D may be involved in resistin regulation through an unknown mechanism. Further studies are recommended to understand resistin regulation in type 1 diabetes.

Renin Phenotypes Characterize Vascular Disease, Autonomous Aldosteronism, and Mineralocorticoid Receptor Activity

CONTEXT

Mild cases of autonomous aldosterone secretion may go unrecognized using current diagnostic criteria for primary aldosteronism (PA).

OBJECTIVE

To investigate whether the inability to stimulate renin serves as a biomarker for unrecognized autonomous aldosterone secretion and mineralocorticoid receptor (MR) activation.

PARTICIPANTS

Six hundred sixty-three normotensive and mildly hypertensive participants, who were confirmed to not have PA using current guideline criteria and were on no antihypertensive medications.

DESIGN

Participants had their maximally stimulated plasma renin activity (PRA) measured while standing upright after sodium restriction. Tertiles of maximally stimulated PRA were hypothesized to reflect the degree of MR activation: lowest PRA tertile = "Inappropriate/Excess MR Activity;" middle PRA tertile = "Intermediate MR Activity;"; and highest PRA tertile = "Physiologic MR Activity." All participants underwent detailed biochemical and vascular characterizations under conditions of liberalized sodium intake, and associations with stimulated PRA phenotypes were performed.

RESULTS

Participants with lower stimulated PRA had greater autonomous aldosterone secretion [higher aldosterone-to-renin ratio (P = 0.002), higher urine aldosterone excretion rate (P = 0.003), higher systolic blood pressure (P = 0.004), and lower renal plasma flow (P = 0.04)] and a nonsignificant trend toward lower serum potassium and higher urine potassium excretion, which became significant after stratification by hypertension status.

CONCLUSIONS

In participants without clinical PA, the inability to stimulate renin was associated with greater autonomous aldosterone secretion, impaired vascular function, and suggestive trends in potassium handling that indicate an extensive spectrum of unrecognized MR activation.

Maternal vitamin D deficiency during pregnancy affects expression of adipogenic-regulating genes peroxisome proliferator-activated receptor gamma (PPARγ) and vitamin D receptor (VDR) in lean male mice offspring

PURPOSE

Maternal vitamin D deficiency during pregnancy is a widespread issue that may have long-lasting consequences on offspring adiposity. We sought to determine how maternal vitamin D deficiency during the perinatal period would affect offspring adipose tissue development and gene expression.

METHODS

Female C57BL/6 J mice were fed either a vitamin D deficient (VDD) or control diet from 4 weeks before pregnancy (periconception) until 7 days postparturition. Male offspring were weighed and euthanized at 75 days of age (early adult period), at which point serum was collected for biochemical analyses, and perigonadal and subcutaneous white adipose tissue (PGAT and SQAT, respectively) were excised, weighed, then flash-frozen for later histology and analyses of adipogenic gene expression.

RESULTS

All adult male offspring were nonobese; there were no significant differences in body weight, adipose pad weight, or adipocyte size. However, VDD-exposed offspring had greater expression of the adipogenic-regulating genes peroxisome proliferator-activated receptor gamma (Pparg) and vitamin D receptor (Vdr).

CONCLUSIONS

This study suggests that exposure to vitamin D deficiency during the perinatal period can directly affect genes involved in the development of adipose tissue in nonobese offspring. These novel findings invite further investigation into the mechanisms by which maternal vitamin D status during pregnancy affects adipose development and metabolic health of offspring.

Adipokines: novel players in resistant hypertension

Resistant hypertension (RH) is a multifactorial disease, frequently associated with obesity and characterized by blood pressure above goal (140/90 mm Hg) despite the concurrent use of ≥3 antihypertensive drugs of different classes. The mechanisms of obesity-related hypertension include, among others, aldosterone excess and inflammatory adipokines, which have demonstrated a significant role in the pathogenesis of metabolic syndrome and RH. This review aims to summarize recent studies on the role of the adipokines leptin, resistin, and adiponectin in the pathophysiology of RH and target-organ damage associated with this condition. The deregulation of adipokine levels has been associated with clinical characteristics frequently recognized in RH such as diabetes, hyperactivity of sympathetic and renin-angiotensin-aldosterone systems, and vascular and renal damage. Strategies to regulate adipokines may be promising for the management of RH and some clinical implications must be considered when managing controlled and uncontrolled patients with RH.

Obesity, adipose tissue function and the role of vitamin D

Introduction

Obesity is not just a cosmetic problem. Pathological accumulation of body fat can cause many health problems: insulin resistance, impaired glucose tolerance, and diabetes mellitus type 2. It may also increase morbidity and mortality. Adipose tissue plays an important role in body homeostasis by producing and secreting several bioactive proteins known as adipokines: adiponectin, leptin, resistin, visfatin, and apelin, which are involved in the regulation of food intake, glucose and lipid metabolism, and insulin action. There can be observed nutritional deficiencies, despite increased food intake, in morbidly obese people. Data concerning concentrations of serum 25(OH)D₃ presented an inverse correlation with obesity parameters like: BMI (body mass index), waist circumference, fat mass or percentage of body fat. Also, higher insulin sensitivity was associated with higher concentrations of vitamin D.

Conclusions

Studies published up to now suggest that vitamin D plays an important role in adipose tissue function and could be involved in the synthesis and modulation of adipokine production. This article is a review of the literature on fatty tissue function and the role of vitamin D in obesity.

Aldosterone dysregulation with aging predicts renal vascular function and cardiovascular risk

Aging and abnormal aldosterone regulation are both associated with vascular disease. We hypothesized that aldosterone dysregulation influences the age-related risk of renal vascular and cardiovascular disease. We conducted an analysis of 562 subjects who underwent detailed investigations under conditions of liberal and restricted dietary sodium intake (1124 visits) in the General Clinical Research Center. Aldosterone regulation was characterized by the ratio of maximal suppression to stimulation (supine serum aldosterone on a liberal sodium diet divided by the same measure on a restricted sodium diet). We previously demonstrated that higher levels of this Sodium-modulated Aldosterone Suppression-Stimulation Index (SASSI) indicate greater aldosterone dysregulation. Renal plasma flow (RPF) was determined via p-aminohippurate clearance to assess basal renal hemodynamics and the renal vascular responses to dietary sodium manipulation and angiotensin II infusion. Cardiovascular risk was calculated using the Framingham Risk Score. In univariate linear regression, older age (β=-4.60; P<0.0001) and higher SASSI (β=-58.63; P=0.001) predicted lower RPF and a blunted RPF response to sodium loading and angiotensin II infusion. We observed a continuous, independent, multivariate-adjusted interaction between age and SASSI, where the inverse relationship between SASSI and RPF was most apparent with older age (P<0.05). Higher SASSI and lower RPF independently predicted higher Framingham Risk Score (P<0.0001) and together displayed an additive effect. Aldosterone regulation and age may interact to mediate renal vascular disease. Our findings suggest that the combination of aldosterone dysregulation and renal vascular dysfunction could additively increase the risk of future cardiovascular outcomes; therefore, aldosterone dysregulation may represent a modifiable mechanism of age-related vascular disease.

Lysine-specific demethylase-1 modifies the age effect on blood pressure sensitivity to dietary salt intake

How interactions of an individual's genetic background and environmental factors, such as dietary salt intake, result in age-associated blood pressure elevation is largely unknown. Lysine-specific demethylase-1 (LSD1) is a histone demethylase that mediates epigenetic regulation and modification of gene transcription. We have shown previously that hypertensive African-American minor allele carriers of the LSD1 single nucleotide polymorphism (rs587168) display blood pressure salt sensitivity. Our goal was to further examine the effects of LSD1 genotype variants on interactions between dietary salt intake, age, and blood pressure. We found that LSD1 single nucleotide polymorphism (rs7548692) predisposes to increasing salt sensitivity during aging in normotensive Caucasian subjects. Using a LSD1 heterozygous knockout mouse model, we compared blood pressure values on low (0.02 % Na(+)) vs. high (1.6 % Na(+)) salt intake. Our results demonstrate significantly increased blood pressure salt sensitivity in LSD1-deficient compared to wild-type animals with age, confirming our findings of salt sensitivity in humans. Elevated blood pressure in LSD1(+/-) mice is associated with total plasma volume expansion and altered renal Na(+) excretion. In summary, our human and animal studies demonstrate that LSD1 is a genetic factor that interacts with dietary salt intake modifying age-associated blood pressure increases and salt sensitivity through alteration of renal Na(+) handling.

Evaluating hormonal mechanisms of vitamin D receptor agonist therapy in diabetic kidney disease: the VALIDATE-D study

BACKGROUND

Insufficient vitamin D status and increased renin-angiotensin system (RAS) activity have been associated with renal-vascular disease and nephropathy in diabetes. Accumulating evidence indicates that vitamin D receptor (VDR) activation lowers unfavorable RAS activity; however, more human intervention studies evaluating whether this mechanism could influence diabetic kidney disease are needed. We previously reported that both vitamin D levels and genetic variation at the VDR predict human RAS activity, and that vitamin D therapy can lower RAS activity in non-diabetics. The VALIDATE-D study is a randomized, placebo-controlled, intervention study designed to extend these findings by evaluating whether direct VDR activation in diabetes lowers circulating and local renal-vascular tissue RAS activity (Aims 1 and 2) in a manner similar to the action of ACE inhibitors (Aim 3).

METHODS/DESIGN

Forty subjects with type 2 diabetes, microalbuminuria, and without chronic kidney disease will be recruited to undergo detailed assessment of the RAS before and after randomization to calcitriol 0.75 mcg/day or placebo. Primary analyses will evaluate whether calcitriol therapy reduces circulating and renal-vascular tissue-RAS activity in comparison to placebo. All subjects will thereafter be treated with lisinopril and followed for 3.5 months to evaluate whether combination therapy (calcitriol + lisinopril vs. placebo + lisinopril) additively or synergistically improves renal-vascular function, and lowers proteinuria.

DISCUSSION

The VALIDATE-D study is the first human intervention study to evaluate whether direct VDR activation can lower the human RAS in diabetes, compared to the effect of an ACE inhibitor, and whether this mechanism can translate to clinically relevant endpoints for diabetic kidney disease. The outcomes of VALIDATE-D will have major implications for the recommendation of vitamin D supplementation for the primary prevention of kidney complications in diabetes.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT01635062.

The influence of sodium- and calcium-regulatory hormone interventions on adipocytokines in obesity and diabetes

OBJECTIVE

The renin-angiotensin-aldosterone system (RAAS), vitamin D, and parathyroid hormone have all been implicated as regulators of adipocytokines and inflammation. We evaluated human interventional study protocols to investigate whether controlled modulations of these calcium- and sodium-regulatory hormones could influence adipocytokines and inflammation in obesity and diabetes.

METHODS

Post-hoc analyses of two separate human protocols (Protocol 1, n=14; Protocol 2, n=24) conducted in a clinical research setting after rigorous control of diet, posture, medications, and diurnal rhythm, were performed. Protocol 1 evaluated obese hypertensives with vitamin D deficiency who received an infusion of angiotensin II (AngII) before and after 1month of vitamin D3 therapy. Protocol 2 evaluated obese subjects with type 2 diabetes who also received AngII. Adipocytokines and inflammatory markers were measured before and after vitamin D3 therapy, and also before and after infusions of AngII.

RESULTS

Vitamin D3 therapy significantly raised 25(OH)D and 1,25(OH)2D concentrations, and lowered parathyroid hormone, but had no effect on concentrations of adiponectin, resistin, leptin, IL-6, PAI-1, urinary TGFβ1, or HOMA-IR. AngII infusions, despite significant elevations in blood pressure and serum aldosterone, did not influence adipocytokine concentrations in either protocol.

CONCLUSION

In contrast to prior studies conducted in healthy populations, or those that could not control major regulators of the RAAS or adipocytokines, we observed that robust modulations in calcium- and sodium-regulatory hormones did not influence adipocytokines or inflammation in obesity or diabetes. Adipose-tissue physiology in these conditions may alter the hormonal regulation of inflammatory parameters.

Vitamin D and vascular disease: the current and future status of vitamin D therapy in hypertension and kidney disease

Over the past decade, vitamin D has generated considerable interest as potentially having important effects on the vasculature and the kidney. Animal and human data indicate that vitamin D suppresses the activity of the renin-angiotensin system and improves endothelial function. Observational studies in humans suggest that low 25-hydroxyvitamin D (25[OH]D) levels are associated with a higher risk of hypertension. However, findings from randomized trials of vitamin D supplementation (with cholecalciferol or ergocalciferol) to lower blood pressure are inconsistent, possibly stemming from variability in study population, sample size, vitamin D dose, and duration. Supplementation with activated vitamin D (i.e., 1,25-dihydroxyvitamin D or analogues) in patients with chronic kidney disease reduces urine albumin excretion, an important biomarker for future decline in renal function. These studies are reviewed, with special emphasis on recent findings. Definitive studies are warranted to elucidate the effects of vitamin D supplementation on mechanisms of hypertension and kidney disease.

The influence of body mass index and renin-angiotensin-aldosterone system activity on the relationship between 25-hydroxyvitamin D and adiponectin in Caucasian men

OBJECTIVE

Previous studies have suggested that circulating adiponectin concentrations are associated positively with vitamin D and negatively with body mass index (BMI) but have not accounted for the influence of the renin-angiotensin-aldosterone system (RAAS) in this relationship. This is particularly relevant because increased RAAS activity is associated with obesity and is known to lower adiponectin levels. We evaluated the association between adiponectin and 25-hydroxyvitamin D (25(OH)D) after controlling RAAS activity with dietary sodium equilibration and also evaluated whether this relationship was influenced by BMI.

DESIGN

Cross-sectional study of 115 hypertensive Caucasian men from the Hypertensive Pathotype Consortium.

METHODS

To manipulate RAAS activity, all subjects underwent 1 week of high dietary sodium (HS) diet to suppress RAAS and 1 week of low dietary sodium (LS) diet to stimulate RAAS. Linear regression was used to evaluate the association between adiponectin and 25(OH)D, and the effect of BMI on this relationship, in each dietary condition.

RESULTS

Adiponectin was higher on HS, where circulating RAAS activity was low, when compared with LS (HS=2.9 versus LS=2.4 μg/ml, P<0.0001). 25(OH)D levels were positively associated with adiponectin, and BMI was a statistically significant effect modifier of the relationship between 25(OH)D and adiponectin on both diets (P interaction <0.01 between BMI and 25(OH)D).

CONCLUSIONS

Higher 25(OH)D concentrations were independently associated with higher adiponectin levels, particularly when BMI was high. Dietary sodium balance and circulating RAAS activity did not appear to affect this relationship. Future studies should explore whether vitamin D supplementation increases adiponectin levels in obesity.