The uncertain significance of low vitamin D levels in African descent populations: a review of the bone and cardiometabolic literature

A Prospective Open-Label Dose-Response Study to Correct Vitamin D Deficiency in Cirrhosis

BACKGROUND

Patients with advanced liver disease often have vitamin D deficiency, but the daily dosages of vitamin D3 needed to raise their serum 25-hydrodroxyvitamin D [25(OH)D] concentrations are unknown.

OBJECTIVE

We aimed to establish the dose-response relationship between vitamin D3 and 25(OH)D in patients with liver cirrhosis.

DESIGN

An open-label study of orally-administered vitamin D3 (gelcaps) was conducted in patients with liver cirrhosis using a tiered-dosing regimen: 4,000 IU/d for baseline 25(OH)D ≤ 15 ng/mL and 2,000 IU/d for baseline 25(OH)D > 15 to ≤ 25 ng/mL (NCT01575717). Supplementation continued for 6 months, or until liver transplantation. Changes in 25(OH)D were measured after ≥ 3 months. Dose-response data on 48 patients (21 receiving 4000 IU/d and 27 receiving 2,000 IU/d) reporting ≥ 80% adherence were analyzed using generalized estimating equations (GEE).

RESULTS

Among the 48 patients, 39 (81%) had 25(OH)D > 20 ng/mL while on supplements, and none experienced hypercalcemia. The magnitude of the increase in 25(OH)D was approximately twofold greater in patients receiving the higher dose. The mean incremental increase was 5.1 ng/ml ± 3.9 of 25(OH)D per 1000 IU/d of vitamin D3. Multivariable models demonstrated a significant positive relationship between baseline 25(OH)D and serum albumin (p < 0.01) and hemoglobin (p = 0.01), and a negative relationship with the MELD score (p < 0.01) and total bilirubin (p < 0.01).

CONCLUSIONS

A two-tiered dosing regimen of daily oral vitamin D3 supplementation safely raised 25(OH)D concentrations in the majority of adults with liver cirrhosis who were adherent to supplement use.

Bariatric surgery, gastrointestinal hormones, and the microbiome: An Obesity Medicine Association (OMA) Clinical Practice Statement (CPS) 2022

Background

This Obesity Medicine Association (OMA) Clinical Practice Statement (CPS) is intended to provide clinicians an overview of bariatric surgery (i.e., bariatric procedures that improve metabolic disease are often termed "metabolic and bariatric surgery"), gastrointestinal hormones, and the microbiome as they relate to patients with obesity.

Methods

The scientific information for this CPS is based upon published scientific citations, clinical perspectives of OMA authors, and peer review by the Obesity Medicine Association leadership.

Results

This CPS includes the pros and cons of the most common types of bariatric procedures; the roles of gastrointestinal (GI) hormones in regulating hunger, digestion, and postabsorptive nutrient metabolism; and the microbiome's function and relationship with body weight. This CPS also describes patient screening for bariatric surgery, patient care after bariatric surgery, and treatment of potential nutrient deficiencies before and after bariatric surgery. Finally, this CPS explores the interactions between bariatric surgery, GI hormones, and the microbiome.

Conclusions

This Obesity Medicine Association (OMA) Clinical Practice Statement (CPS) regarding bariatric surgery, gastrointestinal hormones, and the microbiome is one of a series of OMA CPSs designed to assist clinicians in the care of patients with the disease of obesity. Implementation of appropriate care before and after bariatric surgery, as well as an awareness of GI hormones and the microbiome, may improve the health of patients with obesity, especially patients with adverse fat mass and adiposopathic metabolic consequences.

Vitamin D, skin filaggrin, allergic sensitization, and race

BACKGROUND

In addition to its involvement in both the innate and adaptive immune systems, vitamin D has been found to affect keratinocyte function and proliferation, suggesting a possible role for vitamin D in cutaneous allergic sensitization.

OBJECTIVE

To explore the role of circulating vitamin D levels in allergic sensitization.

METHODS

Serum 25-hydroxyvitamin D (25(OH)D) levels were measured in a subset of children (N = 323) enrolled in the Mechanisms of Progression of Atopic Dermatitis to Asthma in Children cohort, a prospective early life cohort of children with atopic dermatitis. Allergic sensitization was determined using skin prick testing, and FLG expression in the keratinocytes was measured by quantitative polymerase chain reaction. Multiple Poisson regression was used to evaluate interaction effects between serum 25(OH)D levels and FLG expression with sensitization load as the outcome.

RESULTS

Black participants had significantly lower mean levels of serum 25(OH)D compared with non-Black participants (29.3 vs 32.9 ng/mL; P < .001). FLG expression and sensitization load were negatively correlated in non-Black participants with 25(OH)D levels less than 27.2 ng/mL (Rho = -0.45; P = .02). No association between FLG expression and sensitization load was found in Black participants or participants with 25(OH)D levels greater than or equal to 27.2 ng/mL. Multiple Poisson regression models confirmed that 25(OH)D levels interact with FLG expression to affect sensitization load in non-Black participants.

CONCLUSION

Despite lower vitamin D levels in Black participants, sensitization load was associated with nonlesional skin FLG expression in non-Black, but not Black, children with low vitamin D levels. Thus, a complex interplay of factors determines the impact of vitamin D on allergic sensitization.

How Does the Immune System Enter the Brain?

Multiple Sclerosis (MS) is considered the most frequent inflammatory demyelinating disease of the central nervous system (CNS). It occurs with a variable prevalence across the world. A rich armamentarium of disease modifying therapies selectively targeting specific actions of the immune system is available for the treatment of MS. Understanding how and where immune cells are primed, how they access the CNS in MS and how immunomodulatory treatments affect neuroinflammation requires a proper knowledge on the mechanisms regulating immune cell trafficking and the special anatomy of the CNS. The brain barriers divide the CNS into different compartments that differ with respect to their accessibility to cells of the innate and adaptive immune system. In steady state, the blood-brain barrier (BBB) limits immune cell trafficking to activated T cells, which can reach the cerebrospinal fluid (CSF) filled compartments to ensure CNS immune surveillance. In MS immune cells breach a second barrier, the glia limitans to reach the CNS parenchyma. Here we will summarize the role of the endothelial, epithelial and glial brain barriers in regulating immune cell entry into the CNS and which immunomodulatory treatments for MS target the brain barriers. Finally, we will explore current knowledge on genetic and environmental factors that may influence immune cell entry into the CNS during neuroinflammation in Africa.

Obesity history, physical exam, laboratory, body composition, and energy expenditure: An Obesity Medicine Association (OMA) Clinical Practice Statement (CPS) 2022

Background

This Obesity Medicine Association (OMA) Clinical Practice Statement (CPS) on History, Physical Exam, Body Composition and Energy Expenditure is intended to provide clinicians an overview of the clinical and diagnostic evaluation of patients with pre-obesity/obesity.

Methods

The scientific information for this CPS is based upon published scientific citations, clinical perspectives of OMA authors, and peer review by the Obesity Medicine Association leadership.

Results

This CPS outlines important components of medical, dietary, and physical activity history as well as physical exams, with a focus on specific aspects unique to managing patients with pre-obesity or obesity. Patients with pre-obesity/obesity benefit from the same preventive care and general laboratory testing as those without an increase in body fat. In addition, patients with pre-obesity/obesity may benefit from adiposity-specific diagnostic testing - both generally and individually - according to patient presentation and clinical judgment. Body composition testing, such as dual energy x-ray absorptiometry, bioelectrical impedance, and other measures, each have their own advantages and disadvantages. Some patients in clinical research, and perhaps even clinical practice, may benefit from an assessment of energy expenditure. This can be achieved by several methods including direct calorimetry, indirect calorimetry, doubly labeled water, or estimated by equations. Finally, a unifying theme regarding the etiology of pre-obesity/obesity and effectiveness of treatments of obesity centers on the role of biologic and behavior efficiencies and inefficiencies, with efficiencies more often associated with increases in fat mass and inefficiencies more often associated with decreases in fat mass.

Conclusion

The Obesity Medicine Association (OMA) Clinical Practice Statement (CPS) on History, Physical Exam, Body Composition and Energy Expenditure is one of a series of OMA CPSs designed to assist clinicians in the care of patients with the disease of pre-obesity/obesity.

Vitamin D: Possible Therapeutic Roles in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is a unique type of liver cancer instigated by underlying liver diseases. Pre-clinical evidence suggests that HCC progression, like other cancers, could be aided by vitamin D deficiency. Vitamin D is a lipid-soluble hormone usually obtained through sunlight. Vitamin D elucidates its biological responses by binding the vitamin D receptor; thus, promoting skeletal mineralization, and maintain calcium homeostasis. Other reported Vitamin D functions include specific roles in proliferation, angiogenesis, apoptosis, inflammation, and cell differentiation. This review highlighted studies on vitamin D's functional roles in HCC and discussed the specific therapeutic targets from various in vivo, in vitro and clinical studies over the years. Furthermore, it described recent advancements in vitamin D's anticancer effects and its metabolizing enzymes' roles in HCC development. In summary, the review elucidated specific vitamin D-associated target genes that play critical functions in the inhibition of tumorigenesis through inflammation, oxidative stress, invasion, and apoptosis in HCC progression.

Darker Skin Color Measured by Von Luschan Chromatic Scale and Increased Sunlight Exposure Time Are Independently Associated with Decreased Odds of Vitamin D Deficiency in Thai Ambulatory Patients

Background

Little is known about the association among skin color, sunlight exposure. and vitamin D status in Southeast Asian population.

Objective

To investigate the association between skin color measured by von Luschan chromatic scale (VLCS) and vitamin D status in Thai medical ambulatory patients.

Methods

Medical ambulatory patients were enrolled. The eligibility criteria were as follows: aged >18 years, stable medical conditions, and no conditions directly affecting vitamin D status. Serum 25-hydroxyvitamin D [25(OH)D] levels were assessed. Skin color at the outer forearm was assessed using VLCS which grades skin color from the lightest score of 1 to the darkest score of 36. Patients were systematically interviewed to estimate daily sunlight exposure time.

Results

A total of 334 patients were enrolled. Data were expressed as mean ± SD. The mean serum 25(OH)D was 25.21 ± 10.06 ng/mL. There were 17 (5.1%), 217 (65.0%), and 100 (29.9%) patients who had light brown (VLCS score 18–20), medium brown (VLCS score 21–24), and dark brown (VLCS score 25–27) skin colors, respectively. The mean serum 25(OH)D level was higher in patients with dark brown skin than in patients with medium brown and light brown skin (28.31 ± 10.34 vs. 24.28 ± 9.57 and 19.43 ± 9.92 ng/mL, respectively, both p < 0.05). Multivariate analysis showed that darker skin color and increased sunlight exposure time were independently associated with decreased odds of vitamin D deficiency (dark brown vs. light brown: odds ratio, 0.263, 95% CI: 0.081–0.851, p=0.026; medium brown vs. light brown: odds ratio, 0.369, 95% CI: 0.987–1.003, p=0.067; sunlight exposure time odds ratio per 1 minute/day increase 0.955, 95% CI: 0.991–1.000, p=0.037), after adjusting for possible confounders.

Conclusions

We found that darker skin color at sunlight exposure area and increased sunlight exposure time were independently associated with decreased odds of vitamin D deficiency in Thai medical ambulatory patients.

Does solar ultraviolet radiation play a role in COVID-19 infection and deaths? An environmental ecological study in Italy

A significantly stronger impact in mortality and morbidity by COVID-19 has been observed in the northern Italian regions compared to the southern ones. The reasons of this geographical pattern might involve several concurrent factors. The main objective of this work is to investigate whether any correlations exist between the spatial distribution of COVID-19 cases and deaths in the different Italian regions and the amount of solar ultraviolet (UV) radiation at the Earth's surface. To this purpose, in this environmental ecological study a mixed-effect exponential regression was built to explain the incidence of COVID-19 based on the environmental conditions, and demographic and pathophysiologic factors. Observations and estimates of the cumulative solar UV exposure have been included to quantify the amount of radiation available e.g., for pre-vitamin D3 synthesis or SARS-CoV-2 inactivation by sunlight. The analysis shows a significant correlation (p-value <5 × 10^-2) between the response variables (death percentage, incidence of infections and positive tests) and biologically effective solar UV radiation, residents in nursing homes per inhabitant (NHR), air temperature, death percentage due to the most frequent comorbidities. Among all factors, the amount of solar UV radiation is the variable contributing the most to the observed correlation, explaining up to 83.2% of the variance of the COVID-19 affected cases per population. While the statistical outcomes of the study do not directly entail a specific cause-effect relationship, our results are consistent with the hypothesis that solar UV radiation impacted on the development of the infection and on its complications, e.g. through the effect of vitamin D on the immune system or virus inactivation by sunlight. The analytical framework used in this study, based on commonly available data, can be easily replicated in other countries and geographical domains to identify possible correlations between exposure to solar UV radiation and the spread of the pandemic.

Beta cell function, insulin resistance and vitamin D status among type 2 diabetes patients in Western Kenya

Serum vitamin D status exerts effects on glucose-insulin-homeostatic states underlying Diabetes-Mellitus, Type 2 (T2DM). This has been described in white and Asian population where low Vitamin D levels predicted future impairments in beta cell function and worsening of insulin resistance. This study aimed to examine the relationship between serum vitamin D, insulin resistance and beta cell function in a sub population of black Kenyan T2DM patients. The primary objective was to determine the levels of serum 25 hydroxy (25-OH) vitamin D, and estimate the insulin resistance, and beta cell function among T2DM patients at Moi Teaching and Referral Hospital (MTRH). This was a cross sectional study. 124 T2DM patients attending the MTRH Diabetes clinic between February and May 2016 were enrolled. Patients on insulin therapy and/or thiazolidinediones were excluded. Anthropometric, clinical and demographic data was obtained. Samples were drawn for estimation of serum 25-OH vitamin D, fasting insulin levels and fasting blood glucose levels. HOMA (Homeostatic model of assessment) model was used to estimate Beta cell secretion (HOMA-B) and insulin resistance (HOMA-IR); while the Disposition index {(DI) hyperbola product of insulin sensitivity (1/HOMA-IR) and beta cell secretion} was used to estimate the beta cell function. The relationships between serum vitamin D, insulin resistance and beta cell function were explored using a linear regression model. The study participants had a mean age of 56.2 (± 9.2) years, and a mean BMI of 26.9 kg/m² (4.3). Forty nine percent (n = 61) were males. Vitamin D deficiency was present in 71.1% (n = 88) of the respondents. Relatively low levels of insulin resistance and higher levels of beta cell dysfunction were observed {median HOMA-IR of 2.3 (0.7, 6.5) and Disposition Index (DI) of 25.5 (14.3, 47.2)}. Vitamin D levels exhibited a low positive correlation with DI [r = 0.22 (95% CI: 0.03, 0.37)], but was not significantly correlated with HOMA-IR [r = 0.07(95% CI: - 0.11, 0.25)]. These results indicate that beta cell dysfunction rather than insulin resistance as the predominant defect among black T2DM patients seeking care at the MTRH diabetes clinic. Vitamin D deficiency is also prevalent among them and exhibits a low positive correlation with beta cell dysfunction. There was no correlation observed between Vitamin D deficiency and insulin resistance.

Mechanisms of Bone Impairment in Sickle Bone Disease

Sickle bone disease (SBD) is a chronic and invalidating complication of Sickle cell disease (SCD), a multisystem autosomal recessive genetic disorder affecting millions of people worldwide. Mechanisms involved in SBD are not completely known, especially in pediatric age. Among the hypothesized pathogenetic mechanisms underlying SBD are bone marrow compensatory hyperplasia and bone ischemic damage, both secondary to vaso-occlusive crisis (VOC), which leads to cell sickling, thus worsening local hypoxia with a negative impact on osteoblast recruitment. Furthermore, the hypoxia is a strong activator of erythropoietin, which in turn stimulates osteoclast precursors and induces bone loss. Hemolysis and iron overload due to a chronic transfusion regimen could also contribute to the onset of bone complications. Vitamin D deficiency, which is frequently seen in SCD subjects, may worsen SBD by increasing the resorptive state that is responsible for low bone mineral density, acute/chronic bone pain, and high fracture risk. An imbalance between osteoblasts and osteoclasts, with a relative decrease of osteoblast recruitment and activity, is a further possible mechanism responsible for the impairment of bone health in SCD. Moreover, delayed pubertal growth spurt and low peak bone mass may explain the high incidence of fracture in SCD adolescents. The aim of this review was to focus on the pathogenesis of SBD, updating the studies on biochemical, instrumental, and biological markers of bone metabolism. We also evaluated the growth development and endocrine complications in subjects affected with SCD.

Understanding Covid and the associated post-infectious hyper-inflammatory state (PIMS-TS) in children

When SARS-CoV2 infection was first reported from China, very few children had severe lung or systemic disease. Approximately six weeks after the first adult cases were reported in the United Kingdom, a small subgroup of children of largely non-white backgrounds, presented with severe hyper-inflammatory disease, most likely associated with Covid. The possible reasons for this ethnic predilection are explored.

Evaluation of the effectiveness of prophylactic oral vitamin D (cholecalciferol) in children with sickle cell disease

BACKGROUND

Vitamin D (25(OH)D) deficiency has become an emerging public health problem due to its influence on skeletal and extraskeletal diseases. Bone health in patients with sickle cell disease (SCD) is especially compromised and they are more likely to have 25(OH)D deficiency than the general population. Despite this, there is little information on the efficacy of vitamin D3 (vitD3) prophylaxis and its role in improving bone mineral density (BMD) in this population.

PROCEDURES

A prospective, longitudinal, single-center study was conducted with 136 children with SCD monitored at a tertiary referral hospital for SCD. Demographic, clinical and management data, 25(OH)D levels and bone densitometries (DXA) were collected.

RESULTS

Eighty patients were included. There are significant differences between the means of each of 25(OH)D levels as a function of whether the patient started prophylactic treatment as an infant or not (35.71 vs. 27.89 ng/ml, respectively [p = .014]). In multivariate analysis, 800 IU daily dose was shown as a protective factor (p = .044) to reach optimal blood levels (≥30 ng/ml). According to Kaplan-Meier curves, patients younger than 10 years reached optimal levels earlier than older (p = .002), as well as those who were not being treated with hydroxyurea (p = .039).

CONCLUSIONS

VitD3 prophylaxis is a safe practice in SCD. It is important to start this prophylactic treatment when the child is an infant. The daily regimen with 800 IU could be more effective for reaching levels ≥30 ng/ml, and, especially in preadolescent and adolescent patients, we should raise awareness about the importance of good bone health.

Hepatocyte gene expression and DNA methylation as ancestry-dependent mechanisms in African Americans

African Americans (AAs) are an admixed population with widely varying proportion of West African ancestry (WAA). Here we report the correlation of WAA to gene expression and DNA methylation in AA-derived hepatocytes, a cell type important in disease and drug response. We perform mediation analysis to test whether methylation is a mediator of the effect of ancestry on expression. GTEx samples and a second cohort are used as validation. One hundred and thirty-one genes are associated with WAA (FDR < 0.10), 28 of which replicate and represent 220 GWAS phenotypes. Among PharmGKB pharmacogenes, VDR, PTGIS, ALDH1A1, CYP2C19, and P2RY1 nominally associate with WAA (p < 0.05). We find 1037 WAA-associated, differentially methylated regions (FDR < 0.05), with hypomethylated genes enriched in drug-response pathways. In conclusion, WAA contributes to variability in hepatocyte expression and DNA methylation with identified genes previously implicated for diseases disproportionately affecting AAs, including cardiovascular (PTGIS, PLAT) and renal (APOL1) disease, and drug response (CYP2C19).

Biomarkers of Nutrition and Health: New Tools for New Approaches

A main challenge in nutritional studies is the valid and reliable assessment of food intake, as well as its effects on the body. Generally, food intake measurement is based on self-reported dietary intake questionnaires, which have inherent limitations. They can be overcome by the use of biomarkers, capable of objectively assessing food consumption without the bias of self-reported dietary assessment. Another major goal is to determine the biological effects of foods and their impact on health. Systems analysis of dynamic responses may help to identify biomarkers indicative of intake and effects on the body at the same time, possibly in relation to individuals' health/disease states. Such biomarkers could be used to quantify intake and validate intake questionnaires, analyse physiological or pathological responses to certain food components or diets, identify persons with specific dietary deficiency, provide information on inter-individual variations or help to formulate personalized dietary recommendations to achieve optimal health for particular phenotypes, currently referred as "precision nutrition." In this regard, holistic approaches using global analysis methods (omics approaches), capable of gathering high amounts of data, appear to be very useful to identify new biomarkers and to enhance our understanding of the role of food in health and disease.

Is there a relationship between vitamin D nutritional status and metabolic syndrome in childhood acute lymphoblastic leukemia survivors? A PETALE study

BACKGROUND

Treatment of childhood acute lymphoblastic leukemia (cALL) has reached unprecedented success leading to survival rates reaching 90%. This is regrettably linked to increased risk of developing long-term health-related sequels into early adulthood.

OBJECTIVE

This study aims at assessing the relationship between the vitamin D status and metabolic biomarkers in PETALE, a well-characterized cohort of cALL survivors.

RESULTS

We demonstrate that 15.9% of the study participants exhibited 3 or more metabolic syndrome (MetS) risk factors. We also show a direct relationship between s25OHD₃ and plasma HDL-Cholesterol concentrations in female but not male participants.

CONCLUSION

Our data, from a metabolically well-described cohort, support a modest role for vitamin D in lipid metabolism in childhood leukemia survivors. The major outcome of this study is the strong association between HDL-Cholesterol concentration and s25OHD₃ only in female subjects, thereby conveying vitamin D a gender-specific cardio-protective effect. cALL survivors represent a population at higher risk for secondary diseases. For this reason thorough nutritional evaluation, including vitamin D should be part of the regular follow-up.

Endocrine and metabolic complications in children and adolescents with Sickle Cell Disease: an Italian cohort study

BACKGROUND

Children with Sickle Cell Disease (SCD) show endocrine complications and metabolic alterations. The physiopathology of these conditions is not completely understood: iron overload due to chronic transfusions, ischemic damage, and inflammatory state related to vaso-occlusive crises may be involved. Aims of this study were to evaluate the growth pattern, endocrine complications, and metabolic alterations and to detect the relationship between these conditions and the SCD severity in affected children and adolescents.

METHODS

Fifty-two children and adolescents with SCD [38 homozygous sickle hemoglobin (HbSS) and 14 heterozygous sickle hemoglobin (HbSC); age range 3-18 years] were recruited. Anthropometric [height, body mass index (BMI), arm span, sitting height, target height (TH), and pubertal status] and laboratory [blood cell counts, hemolysis indices, metabolic and nutritional status indices and hormonal blood levels] data were evaluated. The SCD severity was defined according to hematological and clinical parameters.

RESULTS

Height-SDS adjusted for TH and BMI-SDS were significantly higher in HbSC children than in HbSS ones. Forty-eight out of 52 patients (92%) had at least one metabolic and/or endocrine alteration: insufficiency/deficiency of vitamin D (84.7%), insulin resistance (11.5%), growth hormone deficiency (3.8%), subclinical hypothyroidism (3.8%), and hypogonadism (1.9%). Levels of vitamin D were significantly and negatively correlated with clinical indicators of the SCD severity. Subjects with HbSS genotype show significant lower levels of both insulin-like growth factor-1 (IGF-1) and insulin-like growth factor binding protein 3 than children with HbSC. In the study population IGF-1 values were significantly and positively correlated with Hb and negatively with lactate dehydrogenase.

CONCLUSIONS

Metabolic alterations and endocrine complications are very common in children and adolescents with SCD. A regular follow-up is necessary to identify subjects at risk for complications to precociously start an appropriate treatment and to improve the quality of life of SCD patients.

CRP Genotypes Predict Increased Risk to Co-Present with Low Vitamin D and Elevated CRP in a Group of Healthy Black South African Women

Low 25-hydroxyvitamin D (25(OH)D) and elevated C-reactive protein (CRP) concentrations are independently associated with adverse health outcomes, including cardiovascular disease (CVD). Although an inverse association between these factors has been described, the underlying mechanisms remain unknown. We postulate that environment-gene interactions, through which 25(OH)D interacts with single nucleotide polymorphisms (SNPs) within the CRP gene, modulate CRP; that certain CRP genotypes predispose individuals to a co-phenotype of low 25(OH)D and elevated CRP concentrations; and that this co-phenotype is associated with higher CVD risk. Twelve CRP SNPs were genotyped, and both 25(OH)D and CRP were quantified, in 505 black South African women. Alarmingly, 66% and 60% of the women presented with deficient/insufficient 25(OH)D and elevated CRP concentrations, respectively. CRP concentrations were higher in individuals with lower 25(OH)D concentrations. However, no 25(OH)D-CRP genotype interactions were evident. Several genotypes were associated with an altered risk of presenting with the co-phenotype, indicating a genetic predisposition. Women presenting with this co-phenotype had higher blood pressure and increased anthropometric measures, which may predispose them to develop CVD. We recommend increasing vitamin D fortification and supplementation efforts to reduce inflammation among black women with vitamin D deficiency, thereby possibly curbing diseases contingent on the co-phenotype described here.

Patterns of vitamin D, parathyroid hormone and c-terminal telopeptide of collagen type 1 in Caucasian and African descent HIV-infected populations in Central Europe

Risk factors for bone loss in HIV patients might differ or have a different impact in African descent compared to Caucasian populations. The aim of the paper is to analyze the relevance of risk factors on surrogate markers of bone metabolism in HIV-infected African descent and Caucasian patients. This is a cross-sectional study in a single HIV-specialized research and clinical care center in Munich, Germany. We included 889 patients in the study, among them 771 Caucasians (86.7%). Only in Caucasians lower vitamin D levels [OR: 2.5 (95CI: 1.6-3.7)], lower calcium levels [OR: 1.8 (1.2-2.8)], and the use of tenofovir disoproxil fumarate [OR: 2.8 (1.8-4.4)] were significantly associated with elevated PTH in multivariate analysis. Likewise, only in Caucasians elevated PTH was significantly associated with elevated markers of c-terminal telopeptides of collagen type 1 (β-CTX) [OR: 1.7 (1.0-3.0)]. Effects of traditional risk factors for secondary hyperparathyroidism and increased markers of bone turn-over seem to be less distinct in African descent HIV patients. The clinical impact and generalizability of this finding as well as the significance of vitamin D supplementation in African descent patients therefore warrants further investigation.

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.

Biochemical and clinical deficiency is uncommon in African immigrants despite a high prevalence of low vitamin D: the Africans in America study

African ancestry is associated with low vitamin D levels but high bone density. Fifty percent of African immigrants had low vitamin D levels, but <10 % had evidence of deficiency. The value of providing vitamin D supplementation to African immigrants without evidence of deficiency needs to be determined.

INTRODUCTION

The Endocrine Society and Institute of Medicine (IOM) have concluded from studies in largely white populations that 25(OH)D is necessary for bone health. However, their definition of vitamin D insufficiency differs. The Endocrine Society recommends a 25(OH)D threshold of <30 ng/mL. The IOM uses a lower threshold of 25(OH)D of <20 ng/mL. As African ancestry is associated with decreased 25(OH)D but increased bone mineral density (BMD), the applicability of these thresholds to Africans is unknown. Therefore, we examined in African immigrants the relationship of 25(OH)D to parathyroid hormone (PTH) and BMD.

METHODS

One hundred eighty-six African immigrants(69 % male, age 38 ± 10 (mean ± SD), range 20-64 years) living in metropolitan Washington, DC, were enrolled. BMD was determined from whole-body dual-energy X-ray absorptiometry (DXA) scans. Decreased BMD required T-scores ≤-1.0. The threshold for low 25(OH)D was the concentration of 25(OH)D at which PTH became suppressed. This is known as the inflection point. Biochemical deficiency required low 25(OH)D and PTH of >65 pg/mL. Clinical deficiency required low 25(OH)D and T-scores ≤-1.0.

RESULTS

25(OH)D <30 and <20 ng/mL occurred in 83 and 46 % of African immigrants, respectively. PTH inversely correlated with 25(OH)D (r = -0.31, P = 0.002). The inflection point occurred at a 25(OH)D concentration of 20 ng/mL. Biochemical and clinical deficiency occurred in only 8 and 3 % of immigrants, respectively.

CONCLUSION

As PTH became suppressed at 25(OH)D of 20 ng/mL, the 25(OH)D <20 ng/mL threshold for insufficiency may apply to African immigrants. However, ~50 % of African immigrants have 25(OH)D <20 ng/mL, but only <10 % had evidence of deficiency. The value of providing vitamin D supplementation to the large number of African immigrants with 25(OH)D <20 ng/mL and no detectable evidence of deficiency needs to be determined.

Vitamin D signaling in calcium and bone homeostasis: a delicate balance

Loss-of-function mutations in genes involved in the vitamin D/vitamin D receptor system have clearly evidenced its critical role for mineral and skeletal homeostasis. Adequate levels of 1,25-dihydroxyvitamin D [1,25(OH)2D], the active form of vitamin D are therefore required and depend on sufficient sunlight exposure or dietary intake. Intestinal calcium absorption is a primary target of 1,25(OH)2D action and this pathway indirectly promotes calcium incorporation in bone. Severe vitamin D deficiency may thus decrease bone quality and leads to osteomalacia, whereas less severe deficiency increases the risk of osteoporosis and bone fractures. On the other hand, high vitamin D levels together with low dietary calcium intake will increase bone resorption and decrease bone mineralization in order to maintain normal serum calcium levels. Appropriate dietary calcium intake and sufficient serum vitamin D levels are thus important for skeletal health. Dosing of calcium and vitamin D supplements is still debated and requires further investigation.

Prevalence of vitamin D deficiency in sickle cell disease: a systematic review

Vitamin D deficiency has emerged as a public health focus in recent years and patients with sickle cell disease (SCD) reportedly have a high prevalence of the condition. Our objectives were to summarize definitions of vitamin D deficiency and insufficiency used in the literature, and to determine the prevalence and magnitude of each in patients with SCD through a systematic review conducted according to PRISMA guidelines. From a PubMed search, 34 potential articles were identified and 15 met eligibility criteria for inclusion. Definitions of deficiency and insufficiency varied greatly across studies making direct comparisons difficult. This review provides evidence to suggest that suboptimal vitamin D levels are highly prevalent among those with SCD, far more so than in comparable non-SCD patients or matched control populations. Defining deficiency as vitamin D <20ng/mL, prevalence estimates in SCD populations range from 56.4% to 96.4%. When compared with results from the population-based National Health and Nutrition Examination Survey, however, the general African American population appeared to have a similarly high prevalence of vitamin D deficiency. African American patients with and without SCD were both substantially higher than that of Caucasians. What remains to be determined is whether there are adverse health effects for patients with SCD because of concurrent vitamin D deficiency.