Vitamin D: Do We Need More Than Sunshine?

There is an astounding amount of conversation and research about vitamin D. It carries many claims, and there is controversy as to what adequate levels should be, how to ensure reaching appropriate serum levels, and what the consequences are of vitamin D insufficiency. This article describes the role of vitamin D, reviews some of the evidence, and provides the current recommendations for vitamin D supplementation, including if a daily walk in the sun is the most appropriate prescription or do we need something more?

Potential immunomodulatory effects of vitamin D in the prevention of severe coronavirus disease 2019: An ally for Latin America (Review)

Currently, the world is under a pandemic of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), responsible for coronavirus disease 2019 (COVID-19). This disease is characterized by a respiratory syndrome that can progress to an acute respiratory distress syndrome. To date, limited effective therapies are available for the prevention or treatment of COVID-19; therefore, it is necessary to propose novel treatment options with immunomodulatory effects. Vitamin D serves functions in bone health and has been recently reported to exert protective effects against respiratory infections. Observational studies have demonstrated an association between vitamin D deficiency and a poor prognosis of COVID-19; this is alarming as vitamin D deficiency is a global health problem. In Latin America, the prevalence of vitamin D deficiency is unknown, and currently, this region is in the top 10 according to the number of confirmed COVID-19 cases. Supplementation with vitamin D may be a useful adjunctive treatment for the prevention of COVID-19 complications. The present review provides an overview of the current knowledge of the potential immunomodulatory effects of vitamin D in the prevention of COVID-19 and sets out vitamin D recommendations for the Latin American population.

Vitamin D analyses in veterinary feeds by gas chromatography-tandem mass spectrometry

This report examines the feasibility of determination of Vitamin D3, D2 and their 25-hydroxy metabolites utilizing Gas Chromatography Tandem Mass Spectrometry (GC/MS/MS) as a potential alternative to popular Liquid Chromatography Tandem Mass Spectrometric (LC/MS/MS) methodologies. The GC/MS/MS approach was found to operate reasonably well despite long-standing concerns that gas-liquid chromatography of vitamin D compounds invoke thermal rearrangements owing to the relatively high inlet and capillary column temperatures used. The workup procedure involved incubation of feed samples with concentrated potassium hydroxide for overnight fat saponification, extraction of D Vitamins in n-hexane and reaction with N,O-bis(trimethylsilyl)trifluoroacetamide at 70 °C for 30 mins. In addition to parent compounds, small amounts of pyro-, isopyro-, and iso-vitamin D and isotachysterol3 variants were obtained from each Vitamin D-related compound upon extraction and GC/MS/MS analysis. Mass spectral and chromatographic behavior of these compounds are herein described and interpreted. Multiple Reaction Monitoring settings on GC/MS/MS included m/z 456→351 for Vitamin D3 and m/z 486→363 for Vitamin D2. Trimethylsilylation enabled single predominant peaks for Vitamins D3 and D2, and sample workup in the presence of deuterated Vitamin D analogs enabled accurate and precise sensitivity to 1 ppb (ng/g) in feeds. The method could be extended with reasonable accuracy to 25-hydroxy (25OH) compounds, but accuracies would be significantly improved by inclusion of respective 25OH-specific deuterated internal standards. The method was applied to 27 submissions of suspect dog foods of which 22% were discovered elevated and 44% were discovered to contain toxic levels of Vitamin D3. The described method was thus discovered to provide a suitable mass spectrometric approach for Vitamin D, proving itself here specifically of value in detection of ergocalciferol and cholecalciferol in animal feeds. The specificity and sensitivity of the tandem quadrupole approach can enable suitable applicability to serum determination if desired.

Vitamin D in human serum and adipose tissue after supplementation

BACKGROUND

Serum 25-hydroxyvitamin D [25(OH)D] concentration is an indicator of vitamin D exposure, but it is also influenced by clinical characteristics that affect 25(OH)D production and clearance. Vitamin D is the precursor to 25(OH)D but is analytically challenging to measure in biological specimens.

OBJECTIVES

We aimed to develop and validate a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for quantification of vitamins D3 and D2 in serum and to explore the potential of circulating vitamin D as a biomarker of exposure in supplementation trials.

METHODS

The method was validated using guideline C62-A from the Clinical and Laboratory Standards Institute and was applied in 2 pilot clinical trials of oral vitamin D3 supplementation. Pilot study 1 included 22 adults randomly assigned to placebo or 2000 IU/d. Blood was collected at baseline, 1, 3, 6, and 12 mo. Pilot study 2 included 15 adults randomly assigned to 2000 or 4000 IU/d. Blood and subcutaneous (SUBQ) adipose tissue were collected at baseline and 3 mo.

RESULTS

In study 1, mean change (baseline to 3 mo) in serum vitamin D3 was -0.1 ng/mL in the placebo group and 6.8 ng/mL in the 2000 IU/d group (absolute difference: 6.9; 95% CI: 4.5, 9.3 ng/mL). In study 2, mean change (baseline to 3 mo) in serum vitamin D3 was 10.4 ng/mL in the 2000 IU/d group and 22.2 ng/mL in the 4000 IU/d group (fold difference: 2.15; 95% CI: 1.40, 3.37). Serum and adipose tissue vitamin D3 concentrations were correlated, and the dose-response of vitamin D3 in adipose mirrored that in serum.

CONCLUSIONS

We validated a sensitive, robust, and high-throughput LC-MS/MS method to quantify vitamins D3 and D2 in serum. Serum and SUBQ adipose tissue vitamin D3 concentrations increased proportionally to dose with 3 mo of daily supplementation.These trials were registered at clinicaltrials.gov as NCT00552409 (pilot study 1) and NCT01477034 (pilot study 2).

Effect of Vitamin D Supplement on Vulvovaginal Atrophy of the Menopause

The effects of oral vitamin D supplements on vaginal health in postmenopausal women with vulvovaginal atrophy (VVA) was evaluated. A double-blinded, randomized placebo-controlled trial was conducted for 12 weeks to investigate changes on vaginal maturation index (VMI), vaginal pH, and the visual analog scale (VAS) of VVA symptoms. The vitamin D group received oral ergocalciferol, at 40,000 IU per week, while the placebo group received an identical placebo capsule. Eighty postmenopausal women were enrolled. There were no significant differences in baseline characteristics between both groups. In an intention-to-treat analysis, VMI, vaginal pH, and VAS of VVA symptoms showed no significant differences between both groups at the six and 12 weeks. However, the mean difference of VMI in the vitamin D group between baseline and at six weeks showed significant improvement (5.5 + 16.27, p <0.05). Moreover, the mean vaginal pH and VAS of VVA patients in the vitamin D group were significantly improved at both six and 12 weeks compared to baseline. The oral vitamin D supplementation for 12 weeks potentially improves vaginal health outcomes in postmenopausal women with VVA symptoms, demonstrated by the improved mean VMI, vaginal pH, and VAS at six and 12 weeks between baseline, however, no significant differences were observed from the placebo treatment.

The role of vitamin D in inflammatory bowel disease: a guide for clinical practice

INTRODUCTION

Inflammatory bowel disease (IBD) is a chronic inflammatory condition of the gastrointestinal tract that carries significant morbidity and mortality. Given the need to identify modifiable risk factors to prevent IBD development and to mitigate disease severity, vitamin D has become a major candidate of interest.

AREAS COVERED

In this review, we discuss the regulatory role played by vitamin D in intestinal immune homeostasis, updates in the recent literature exploring its role in de novo IBD pathogenesis and established IBD activity. We also discuss societal recommendations on its therapeutic role in maintaining bone health and future directions for studying its role in regulating disease activity.

EXPERT OPINION

In contrast to findings from earlier studies suggesting a causal role in IBD, recent findings indicate that vitamin D deficiency may be a sequela rather than a cause of IBD. Additionally, clinical trials exploring vitamin D therapy in reducing disease activity remain inconclusive thus far, with the current evidence best supporting a therapeutic role of vitamin D in bone health. Future studies are needed to clarify the role of vitamin D in IBD development and disease activity and to determine its therapeutic potential for IBD disease activity.

[Method Verification for Vitamin D Analysis in Processed Foods Based on the Analytical Manual for the Standard Tables of Food Composition in Japan 2015 (Seventh Revised Edition)]

Considerable amounts of processed foods contain vitamin D (ergocalciferol (D₂) and cholecalciferol (D₃)) as food additives. For field surveys on food additives, the analytical method for vitamin D should be well-validated. However, the current official method in Japan cannot separately determine the concentrations of D₂ and D₃, whereas the method for the Standard Tables of Food Composition in Japan 2015 (STFC method) can. Therefore, in this study, we verified the applicability of the STFC method to processed foods. During the course of this research, we added some improvements to the original method. Spike and recovery experiments using vegetable juice, soymilk, and corn flakes as food matrices showed that the recovery rates (relative standard deviation) of D₂ and D₃ were 103-112% (4.7-12.6%) and 102-109% (2.4-21.8%), respectively, at the estimated method limit of quantification (EMLOQ) level; and 100-110% (4.0-7.4%) and 102-105% (3.8-4.8%), respectively, at 10 times the EMLOQ level. These results indicated that accuracy and precision of the modified STFC method were enough to determine dietary D₂ and D₃ as endogenous nutrients and/or food additives, and suggested that this method is appropriate for analyzing vitamin D concentrations in processed foods.

Ergocalciferol improves endothelial vasodilatory and vasoconstrictor function in an in vivo model of mild uraemia

Endothelial dysfunction and vitamin D deficiency are prevalent in patients with cardiovascular disease (CVD) and chronic kidney disease (CKD). Both are risk factors for cardiovascular events in patients with CKD. No studies have investigated the effect of nutritional forms of vitamin D on endothelial function in earlier stages of CKD, when vascular endothelium may be more amenable to this therapy. We studied the effect of ergocalciferol in a pre-clinical model of mild uraemia.

Male Wistar rats underwent either a 5/6th nephrectomy or sham surgery. Four weeks after the final stage of the surgery, these two groups were randomly allocated to placebo or an oral dose of 1000 iu of ergocalcfierol at day 7 and 2 pre sacrifice. Vascular responses to acetylcholine, Spermine NONOate and phenylephrine were determined in aortic rings. Blood pressure, calcium, phosphate and parathyroid hormone were measured in all groups.

Ergocalciferol significantly improved the endothelium-dependent responses to acetylcholine and overcame the blunting of the contractile response to phenylephrine seen in uraemic animals. Ergocalciferol improved the contractile response to potassium chloride in uraemic, but not sham animals. All effects occurred independently of changes to calcium, phosphate, parathyroid hormone and systolic blood pressure. There were no differences in endothelium-independent relaxation to Spermine NONOate.

In summary, in a model of mild uraemia, ergocalciferol improved vasodilator and vasoconstrictor tone independently of blood pressure and bone mineral parameters suggesting a direct effect of ergocalciferol on the endothelium.

Vitamin D Supplementation for Extraskeletal Indications in Older Persons

Low levels of vitamin D have been implicated in a wide variety of conditions highly prevalent in the geriatric population, including fractures, functional limitations, cancer, cardiovascular disease, and depression. Vitamin D supplementation is often considered integral to the prevention of falls and fractures in the setting of osteoporosis. For other conditions, however, consensus is lacking, and the clinician may struggle to balance competing recommendations around screening, supplementation, and monitoring. This review seeks to provide an overview of the available evidence on the use of vitamin D supplementation to ameliorate sarcopenia, enhance cognition, treat depression, prevent cancer, and reduce mortality-outcomes that are common concerns in the geriatric population for which the merits of treatment are not always certain. Evidence suggests vitamin D supplementation may decrease mortality. Therefore, it may be reasonable to prescribe routine supplementation with oral cholecalciferol 800 to 1000 IU daily to all patients aged ≥65 years who do not have a contraindication. No screening or monitoring would be recommended for this population. We additionally recommend the use of oral cholecalciferol over ergocalciferol for any routine supplementation as this benefit was only observed with cholecalciferol. For patients with depression or cognitive disorders, we recommend screening for vitamin D deficiency, treating with oral cholecalciferol if present, and monitoring periodically to target a level of >30 ng/mL as an adjunct to usual care. The level of evidence certainly would not justify the use of vitamin D in place of more evidence-based therapies, but given the burden of these conditions in the geriatric population, we believe the potential benefit justifies the minimal risk.

Vitamin D, menopause, and aging: quo vadis?

Menopause and aging are associated with changes in circulating gonadal steroid hormones, insulin sensitivity, body composition, and also lifestyle and social coordinates. Vitamin D status influences different metabolic adjustments, aside from calcium-phosphorus and bone metabolism. The main blood marker used to measure endogenous vitamin D status is 25-hydroxyvitamin D. Aging is associated with increases in serum parathyroid hormone and alkaline phosphatase, and a decrease of serum calcium, phosphorus, and vitamin D metabolites. 25-Hydroxyvitamin D status is also influenced by the circannual rhythm of sun irradiation. Results of clinical association studies have not correlated with intervention trials, experimental studies, and/or meta-analyses regarding the role of vitamin D on different outcomes in women during their second half of life and the vitamin D supplementation dose needed to improve clinical endpoints. Discordant results have been related to the method used to measure vitamin D, the studied population (i.e., sociodemographics and ethnicity), study designs, and biases of analyses. Vitamin D supplementation with cholecalciferol or calcifediol may improve some metabolic variables and clinical outcomes in young postmenopausal and older women. Studies seem to suggest that calcifediol may have some advantages over other forms of vitamin D supplementation. Further studies are needed to define interventions with supplements and effective food fortification.

Electrochemical Oxidation as a Tool for Generating Vitamin D Metabolites

The electrochemical behavior of the vitamers cholecalciferol and ergocalciferol was investigated in order to determine whether it is possible to evaluate phase-I and phase-II metabolism of these steroids and yield metabolites that can serve as reference material. The vitamers were electrochemically-oxidized using an electrochemical system (ROXY™ EC system). The influence of pH value, solvent, and potential was evaluated. When using methanol or ethanol, the formation of artificial methoxy or ethoxy groups, respectively, was observed, while the use of acetonitrile did not show any formation of further functional groups. A neutral pH value and use of a constant potential led to the highest number of oxidation products with intensive signals. Additionally, a binding study between vitamin D and glucuronic acid as an example for phase-II conjugation was carried out. It was possible to detect adduct formation. Coupling mass spectrometry directly to electrochemistry (EC-MS) is a promising approach for generating vitamin D metabolites and/or yielding a number of metabolites without in vivo or in vitro test systems. It can support or even replace animal studies in the long-term and might be promising for yielding reference compounds.

Recent Advances in Formulation Strategies for Efficient Delivery of Vitamin D

Deficiency of vitamin D is a global concern affecting a huge number of human populations. This deficiency has a serious impact on human health not only affecting bone mineral density but also becoming the reason for cardiovascular disorders, infectious diseases, autoimmune diseases and cancers. Exposure to sunlight is the major source of vitamin D, but due to the present day-to-day lifestyle of working in a shade arouses the need for exogenous sources of vitamin D. Ergocalciferol (vitamin D2) and cholecalciferol (vitamin D3) are the two major forms of vitamin D, which are hydrophobic in nature and highly susceptible to environmental conditions, like temperature and light. Therefore, novel drug delivery systems could be explored for efficient delivery of vitamin D. In this review, a brief account of vitamin D is provided followed by a detailed description of recent advances in various delivery systems, including solid lipid nanoparticles, nanoemulsion, self-emulsifying drug delivery systems, polymeric nanoparticles and solid dispersion, for the efficient delivery of vitamin D.

The effect of vitamin D2 supplementation on muscle strength in early postmenopausal women: a randomized, double-blind, placebo-controlled trial

BACKGROUND

Low serum 25-hydroxyvitamin D [25(OH)D] has been shown to be associated with low muscle mass and loss of muscle strength, resulting in increased disability and frailty in older men and women. Vitamin D deficiency is common in postmenopausal women. The primary objective of the present study was to evaluate the effects of vitamin D supplementation on muscle strength in early postmenopausal women. The effects of vitamin D2 supplementation on muscle mass and muscle cross-sectional area (CSA) were secondarily investigated.

METHODS

A 12-week, prospective, randomized, double-blind, placebo-controlled trial was conducted in early postmenopausal women (45-60 years old) with vitamin D deficiency (serum 25(OH)D < 20 ng/ml). A total of 88 subjects were randomized into group I: vitamin D2 supplement 40 000 IU/week (n = 44), or group II: placebo (n = 44). Serum 25(OH)D level, muscle strength, muscle mass and muscle CSA were assessed at baseline and 12 weeks after the supplementation.

RESULTS

After 12 weeks of supplementation, 70% of women in group I achieved a sufficient level of serum 25(OH)D (>30 ng/ml). There were significant differences in changes of serum 25(OH)D levels between the two groups (p < 0.05). Muscle strength and muscle CSA in group I increased significantly after 12 weeks (p = 0.015, 0.045, respectively). However, there were no significant differences in the mean changes of muscle strength, muscle mass and muscle CSA between the two groups (p = 0.16, 0.89, 0.84, respectively).

CONCLUSION

In this study, we found no obvious effect of vitamin D supplementation on the changes in muscle strength, muscle mass and muscle CSA when compared to placebo. However, there were significant changes in muscle strength and muscle CSA from baseline in the vitamin D supplementation group.

Prevalence of Vitamin D Deficiency and Associated Risk Factors in the US Population (2011-2012)

Introduction

1,25-dihydroxyvitamin D3 (cholecalciferol), the hormonally active form of vitamin D3, is a lipid-soluble compound that plays a significant role in clinical medicine due to its potent effects on calcium homeostasis and bone metabolism. Since foods containing natural vitamin D are rare, the primary source of the compound remains its nonenzymatic dermal synthesis through exposure to ultraviolet rays in sunlight. Although uncommon in most developed countries, recent literature has demonstrated that subclinical vitamin D deficiency can exist in certain populations and plays a role in downstream clinical consequences, including cardiovascular disease, cancer, diabetes, osteoporosis, and fractures. This study aims to identify the prevalence and change in the pattern of vitamin D deficiency in subpopulations throughout the United States to provide a foundation for further clinical studies correlating the clinical outcomes to vitamin deficiency.

Methods

Data analyzed in this study were collected through National Health and Nutrition Examination Survey (NHANES), specifically from a population of 4962 participants, age ≥20 years, who were hospitalized between 2011 and 2012. This cohort was stratified to divide the population into patients that were vitamin D sufficient (>50 nmol/L) versus patients who were vitamin D deficient (50 nmol/L). The risk factors were compared between the subpopulations in 2005-2006 and 2011-2012.

Conclusions

The prevalence of vitamin D deficiency is greater in certain clinical subpopulations, and the presence of associated characteristics should raise the index of suspicion for the practicing clinician with regard to conditions associated with vitamin D deficiency, such as osteoporosis and osteomalacia. Further research investigating the pathophysiology of hypovitaminosis D and its clinical consequences can help better understand and prevent the development of associated comorbidities.

Italian Association of Clinical Endocrinologists (AME) and Italian Chapter of the American Association of Clinical Endocrinologists (AACE) Position Statement: Clinical Management of Vitamin D Deficiency in Adults

Vitamin D deficiency is very common and prescriptions of both assay and supplementation are increasing more and more. Health expenditure is exponentially increasing, thus it is timely and appropriate to establish rules. The Italian Association of Clinical Endocrinologists appointed a task force to review literature about vitamin D deficiency in adults. Four topics were identified as worthy for the practicing clinicians. For each topic recommendations based on scientific evidence and clinical practice were issued according to the Grading of Recommendations, Assessment, Development, and Evaluation (GRADE) System. (1) What cut-off defines vitamin D deficiency: even though 20 ng/mL (50 nmol/L) can be considered appropriate in the general population, we recommend to maintain levels above 30 ng/mL (75 nmol/L) in categories at risk. (2) Whom, when, and how to perform screening for vitamin D deficiency: categories at risk (patients with bone, liver, kidney diseases, obesity, malabsorption, during pregnancy and lactation, some elderly) but not healthy people should be screened by the 25-hydroxy-vitamin D assay. (3) Whom and how to treat vitamin D deficiency: beyond healthy lifestyle (mostly sun exposure), we recommend oral vitamin D (vitamin D2 or vitamin D3) supplementation in patients treated with bone active drugs and in those with demonstrated deficiency. Dosages, molecules and modalities of administration can be profitably individually tailored. (4) How to monitor the efficacy of treatment with vitamin D: no routine monitoring is suggested during vitamin D treatment due to its large therapeutic index. In particular conditions, 25-hydroxy-vitamin D can be assayed after at least a 6-month treatment. We are confident that this document will help practicing clinicians in their daily clinical practice.

Effect of vitamin D treatments on plasma metabolism and immune parameters of healthy dairy cows

The objective of this study was to investigate the possible beneficial effect of vitamin D repletion on certain immune parameters of vitamin D insufficient dairy cows. Twenty dairy cows in late lactation were treated daily with vitamin D in five different ways: sunlight exposure (SUN), D₂ supplementation combined with sunlight exposure (D2SUN), D₂ supplementation (D2), D₃ supplementation (D3), and D₂ and D₃ supplementation combined (D2D3). The cows had very low vitamin D levels at d 0 because of the vitamin D deprivation before the study. After 1 month of vitamin D repletion, all cows had plasma 25(OH)D levels within the normal range. Total 25(OH)D concentration was significantly higher in SUN, D2SUN and D2D3 than D2 or D3 at the end of the study. However, milk yield, as well as protein and fat content of the milk, was not influenced by vitamin D treatments. There was no difference obtained in the measured immune parameters: Leucocyte populations, somatic cell count, immunoglobulin concentrations in plasma and milk, and antigen-stimulated cytokine productions did not change in response to vitamin D repletion or difference in vitamin D sources, and no relations to plasma 25(OH)D levels were identified. Despite the fact that plasma 25(OH)D increased from a very low level to normal range, the present study did not show any effect of vitamin D repletion on the tested immune parameters of healthy dairy cows. Therefore, in this study, it was concluded that repletion to physiologically normal plasma 25-hydroxyvitamin D levels of vitamin D-depleted healthy dairy cows had no influence on immune parameters.

Current knowledge of vitamin D in dogs

There is emerging interest in linking vitamin D status to physiological health and disease states in the dog, as evidenced by the recent increase in publications in this area. This research has most likely been spurred by the studies exploring vitamin D and disease in humans. However, there are important differences in vitamin D intake and metabolism between humans and dogs that should be accounted for. The understanding of basic vitamin D metabolism and the relationship between vitamin D intake and vitamin D status in dogs remains even more limited than current knowledge in humans. This review will summarize current knowledge of vitamin D in the dog, including metabolism and dietary recommendations. Emphasis is placed on the limitations to current knowledge. Studies investigating links between vitamin D and disease will be discussed in light of this knowledge. Suggestions for future research, including the development of reference ranges to define blood vitamin D sufficiency, are provided.

The Association between Vitamin D Insufficiency and Nonalcoholic Fatty Liver Disease: A Population-Based Study

Previous studies have shown inconsistent results regarding the association between vitamin D insufficiency and nonalcoholic fatty liver disease (NAFLD). We attempted to demonstrate this relationship using population-based data. Vitamin D insufficiency was defined as a 25(OH)D level ≤20 ng/mL. Hepatic steatosis index was calculated to define NAFLD. Significant fibrosis was assessed using Body mass index, AST/ALT Ratio, Diabetes (BARD) score. Logistic regression analyses were performed to determine the relationship between vitamin D insufficiency and NAFLD. Among 1812 participants, 409 (22.6%) had NAFLD. Patients with nonalcoholic fatty liver disease were more likely to be male (56.7%), had higher body mass index (28.1 kg/m²), and had more metabolic syndrome (57.2%). The proportion of vitamin D insufficiency did not differ between NAFLD and non-NAFLD (77.5% vs. 77.4%). Logistic regression analyses showed that BMI, diabetes, and triglyceride level were significantly associated with NAFLD, whereas vitamin D insufficiency was not related. Subgroup analyses involving non-obese participants, male participants, and participants without metabolic syndrome showed similar results. The BARD score and the proportion of significant fibrosis by BARD score did not differ according to vitamin D status. Vitamin D insufficiency was not associated with the presence of NAFLD as assessed by validated noninvasive prediction models.

Vitamin D prohormone in the treatment of secondary hyperparathyroidism in patients with chronic kidney disease

Secondary hyperparathyroidism (sHPT) represents the adaptive and very often, finally, maladaptive response of the organism to control the disturbed homeostasis of calcium, phosphorus, and vitamin D metabolism caused by declining renal function in chronic kidney disease (CKD). sHPT leads to cardiovascular and extravascular calcifications and is directly linked to an increased risk of cardiovascular morbidity and mortality as well as excess all-cause mortality. Vitamin D plays an important role in the development of sHPT. CKD patients are characterized by a high prevalence of hypovitaminosis D. Supplementation with both vitamin D prohormones cholecalciferol and ergocalciferol enables the achievement and maintenance of a normal vitamin D status when given in adequate doses over an appropriate treatment period. In patients with earlier stages of CKD, sHPT is influenced by and can be successfully treated with vitamin D prohormone supplementation, whereas in patients with very late stages of CKD and those requiring dialysis, treatment with prohormones seems to be of limited efficacy. This review gives an overview of the pathogenesis of sHPT, summarizes vitamin D metabolism, and discusses the existing literature regarding the role of vitamin D prohormone in the treatment of sHPT in patients with CKD.

Role of Vitamin D in Inflammatory Bowel Disease

Vitamin D is a secosteroid hormone that possesses immunomodulatory properties and has been demonstrated to potentially influence inflammatory bowel disease (IBD) pathogenesis and activity. Epidemiologic data have associated vitamin D deficiency with an increased risk of IBD, hospitalizations, surgery, and loss of response to biologic therapy. Conversely, IBD itself can lead to vitamin D deficiency. This bidirectional relationship between vitamin D and IBD suggests the need for monitoring and repletion of vitamin D, as needed, in the IBD patient. This review discusses the role of vitamin D in IBD and provides practical guidance on vitamin D repletion.

Vitamin D bioavailability: state of the art

There has been renewed interest in vitamin D since numerous recent studies have suggested that besides its well-established roles in bone metabolism and immunity, vitamin D status is inversely associated with the incidence of several diseases, e.g., cancers, cardio-vascular diseases, and neurodegenerative diseases. Surprisingly, there is very little data on factors that affect absorption of this fat-soluble vitamin, although it is acknowledged that dietary vitamin D could help to fight against the subdeficient vitamin D status that is common in several populations. This review describes the state of the art concerning the fate of vitamin D in the human upper gastrointestinal tract and on the factors assumed to affect its absorption efficiency. The main conclusions are: (i) ergocalciferol (vitamin D2), the form mostly used in supplements and fortified foods, is apparently absorbed with similar efficiency to cholecalciferol (vitamin D3, the main dietary form), (ii) 25-hydroxyvitamin D (25OHD), the metabolite produced in the liver, and which can be found in foods, is better absorbed than the nonhydroxy vitamin D forms cholecalciferol and ergocalciferol, (iii) the amount of fat with which vitamin D is ingested does not seem to significantly modify the bioavailability of vitamin D3, (iv) the food matrix has apparently little effect on vitamin D bioavailability, (v) sucrose polyesters (Olestra) and tetrahydrolipstatin (orlistat) probably diminish vitamin D absorption, and (vi) there is apparently no effect of aging on vitamin D absorption efficiency. We also find that there is insufficient, or even no data on the following factors suspected of affecting vitamin D bioavailability: (i) effect of type and amount of dietary fiber, (ii) effect of vitamin D status, and (iii) effect of genetic variation in proteins involved in its intestinal absorption. In conclusion, further studies are needed to improve our knowledge of factors affecting vitamin D absorption efficiency. Clinical studies with labeled vitamin D, e.g., deuterated or (13)C, are needed to accurately and definitively assess the effect of various factors on its bioavailability.

Prospective, Randomized, Double-Blind, Parallel-Group, Comparative Effectiveness Clinical Trial Comparing a Powder Vehicle Compound of Vitamin D With an Oil Vehicle Compound in Adults With Cystic Fibrosis

BACKGROUND

There is little consensus on the most efficacious vehicle substance for vitamin D supplements. Fat malabsorption may impede the ability of patients with cystic fibrosis (CF) to absorb vitamin D in an oil vehicle. We hypothesized that vitamin D contained in a powder vehicle would be absorbed more efficiently than vitamin D contained in an oil vehicle in patients with CF.

METHODS

In this double-blind, randomized controlled trial, hospitalized adults with CF were given a one-time bolus dose of 100,000 IU of cholecalciferol (D₃) in a powder-based or oil-based vehicle. Serum D₃, 25-hydroxyvitamin D, and parathyroid hormone concentrations were analyzed at 0, 12, 24, and 48 hours posttreatment. The area under the curve for serum D₃ and the 12-hour time point were also assessed as indicators of D₃ absorption.

RESULTS

This trial was completed by 15 patients with CF. The median (interquartile range) age, body mass index, and forced expiratory volume in 1 second were 23.7 (19.9-33.2) years, 19.9 (18.6-22.6) kg/m², and 63% (37%-80%), respectively. The increase in serum D₃ and the area under the curve was greater in the powder group ( P = .002 and P = .036, respectively). Serum D₃ was higher at 12 hours in the powder group compared with the oil group ( P = .002), although levels were similar between groups by 48 hours.

CONCLUSIONS

In adults with CF, cholecalciferol is more efficiently absorbed in a powder compared with an oil vehicle. Physicians should consider prescribing vitamin D in a powder vehicle in patients with CF to improve the absorption of vitamin D from supplements.

Dose-Response Effect of Sunlight on Vitamin D2 Production in Agaricus bisporus Mushrooms

The dose response effect of UV-B irradiation from sunlight on vitamin D2 content of sliced Agaricus bisporus (white button mushroom) during the process of sun-drying was investigated.Real-time UV-B and UV-A data were obtained using a high-performance spectroradiometer. During the first hour of sunlight exposure, the vitamin D2 content of the mushrooms increased in a linear manner, with concentrations increasing from 0.1 μg/g up to 3.9 ± 0.8 μg/g dry weight (DW). At the subsequent two measurements one and 3 h later, respectively, a plateau was reached. Two hours of additional exposure triggered a significant decline in vitamin D2 content. After just 15 min of sun exposure and an UV-B dose of 0.13 J/cm(2), the vitamin D2 content increased significantly to 2.2 ± 0.5 μg/g DW (P < 0.0001), which is equivalent to 17.6 μg (704 IU) vitamin D2 per 100 g of fresh mushrooms and comparable to levels found in fatty fish like the Atlantic salmon.

More than healthy bones: a review of vitamin D in muscle health

Vitamin D has known importance to bone health including calcium and phosphate homeostasis and appears to have a role in skeletal muscle health as well. Cases of vitamin D deficiency and insufficiency have been associated with poor muscle health. While the exact effects and mechanism of action remains controversial, current data lean towards insufficient vitamin D playing a role in musculoskeletal pain, sarcopenia, myopathy, falls and indirectly via cerebellar and cognitive dysfunction. Sophisticated experimental techniques have allowed detection of the vitamin D receptor (VDR) on skeletal muscle and cerebellar tissue, which if validated in further large studies, could confirm the mechanism of vitamin D in these associations. While further study is required, vitamin D repletion can have a substantial impact on muscle as well as bone health.

Insulin secretion and sensitivity in healthy adults with low vitamin D are not affected by high-dose ergocalciferol administration: a randomized controlled trial

BACKGROUND

Epidemiologic data suggest that low serum 25-hydroxyvitamin D [25(OH)D] increases insulin resistance and the risk of type 2 diabetes. Few interventional trials have assessed the effect of vitamin D on insulin metabolism, and published results are discordant.

OBJECTIVE

The goal of this study was to perform a detailed assessment of the effect of ergocalciferol administration on glucose and insulin metabolism in healthy people with low total 25(OH)D(total).

DESIGN

This was a 12-wk, double-blinded, randomized controlled trial. We enrolled 90 healthy volunteers aged 18-45 y with serum 25(OH)D ≤20 ng/mL (by immunoassay) and administered 50,000 IU ergocalciferol/wk or placebo for 12 wk. Primary endpoints were change in first-phase insulin response and insulin sensitivity as measured by intravenous glucose tolerance test. Secondary endpoints included change in homeostasis model assessment of insulin resistance; fasting glucose, insulin, and lipids; body mass index (BMI); and blood pressure.

RESULTS

On-study 25(OH)D(total) was assessed by liquid chromatography-tandem mass spectrometry. In the treated group, 25(OH)D(total) rose from 18 ± 7 to 43 ± 12 ng/mL (P < 0.001) with no change in the placebo group. Despite this increase, at 12 wk, there were no between-group differences in either insulin response or insulin sensitivity; nor were there differences in any measured secondary endpoints. There was no evidence of effect modification by sex, race, glucose tolerance status, baseline 25(OH)D(total), or BMI.

CONCLUSION

In healthy persons with low 25(OH)D(total), ergocalciferol administration for 12 wk normalizes 25(OH)D(total) but does not improve insulin secretion, insulin sensitivity, or other markers of metabolic health.