Vitamin D Binding Protein, Total and Free Vitamin D Levels in Different Physiological and Pathophysiological Conditions

Vitamin D Metabolites: Analytical Challenges and Clinical Relevance

Recent research activities have provided new insights in vitamin D metabolism in various conditions. Furthermore, substantial progress has been made in the analysis of vitamin D metabolites and related biomarkers, such as vitamin D binding protein. Liquid chromatography tandem mass spectrometric (LC-MS/MS) methods are capable of accurately measuring multiple vitamin D metabolites in parallel. Nevertheless, only 25(OH)D and the biologically active form 1,25(OH)2D are routinely measured in clinical practice. While 25(OH)D remains the analyte of choice for the diagnosis of vitamin D deficiency, 1,25(OH)2D is only recommended in a few conditions with a dysregulated D metabolism. 24,25(OH)2D, free and bioavailable 25(OH)D, and the vitamin D metabolite ratio (VMR) have shown promising results, but technical pitfalls in their quantification, limited clinical data and the lack of reference values, impede their use in clinical practice. LC-MS/MS is the preferred method for the measurement of all vitamin D related analytes as it offers high sensitivity and specificity. In particular, 25(OH)D and 24,25(OH)2D can accurately be measured with this technology. When interpreted together, they seem to provide a functional measure of vitamin D metabolism beyond the analysis of 25(OH)D alone. The determination of VDBP, free and bioavailable 25(OH)D is compromised by unresolved analytical issues, lacking reference intervals and insufficient clinical data. Therefore, future research activities should focus on analytical standardization and exploration of their clinical value. This review provides an overview on established and new vitamin D related biomarkers including their pathophysiological role, preanalytical and analytical aspects, expected values, indications and influencing conditions.

The plasma free fraction of 25-hydroxyvitamin D3 is not strongly associated with 25-hydroxyvitamin D3 clearance in kidney disease patients and controls

Circulating 25-hydroxyvitamin D [25(OH)D] concentration is used to monitor vitamin D status. Plasma protein binding may influence the 25(OH)D dose-response to vitamin D treatment through a direct relationship between the plasma unbound ("free") fraction and clearance of 25(OH)D. We previously evaluated 25(OH)D3 clearance in relation to kidney function using intravenous administration of deuterium labeled 25(OH)D3. In this follow up study, we determined the free fraction of 25(OH)D3 in plasma (i.e., percent free 25(OH)D3) and the serum concentration and haplotype of vitamin D binding protein in these participants. We hypothesized that the percent free 25(OH)D3 would be positively associated with 25(OH)D3 clearance and would mediate associations between clearance and vitamin D binding protein (GC) haplotypes. Participants were mean (SD) age 64 (10) years and included 42 individuals with normal kidney function (controls), 24 individuals with chronic kidney disease, and 19 individuals with kidney failure on hemodialysis. Free plasma 25(OH)D2 and 25(OH)D3 concentrations were quantified with a new liquid chromatography-tandem mass spectrometry (LC-MS/MS) method. Because there is no reference measurement procedure for free 25(OH)D, we compared the new method with a widely-used predictive equation and a commercial immunoassay. The percent free 25(OH)D3 determined by predictive equation was weakly associated with 25(OH)D3 clearance (R = 0.27; P = 0.01). However, this association was absent when percent free 25(OH)D3 was determined using LC-MS/MS-measured free and total 25(OH)D3 concentrations. Method comparison uncovered a negative bias in immunoassay-measured free 25(OH)D concentrations among participants with kidney failure, so immunoassay results were not used to evaluate the association between percent free 25(OH)D3 and clearance. GC2 haplotype carriage was associated with 25(OH)D3 clearance. Among individuals with 2 relative to no GC2 alleles, clearance was 87 (95% CI: 15-158) mL/d greater. However, in contrast with the literature, GC2 carriage was not significantly related to DBP concentration or the percent free 25(OH)D3 (either predicted or measured). In conclusion, the free fraction of 25(OH)D3 is not strongly associated with 25(OH)D3 clearance but may explain small differences in clearance according to GC haplotype.

Genetic Variations of the Vitamin D Metabolic Pathway and COVID-19 Susceptibility and Severity: Current Understanding and Existing Evidence

The immunomodulatory and metabolic effects of vitamin D receptor (VDR) activation have been considered beneficial in mitigating the susceptibility and severity of COVID-19 infection. Furthermore, vitamin D-binding protein (DBP) has pleiotropic effects on the immune system that may influence inflammation associated with COVID-19. Multiple observational studies have demonstrated an association between low levels of serum 25-hydroxyvitamin D and risk and the severity of COVID-19 infection. However, the impact of vitamin D supplementation as an adjunctive treatment for COVID-19 based on evidence from randomized clinical trials is unclear. Equally important is that certain variations of the genes involved in the vitamin D metabolic pathway have been shown to affect immune function and linked with various clinical outcomes, including cardio-metabolic disorders, autoimmune diseases, infections, and cancers. This indicates inter-individual difference in body response to vitamin D. There is also emerging evidence that common polymorphisms of these genes may influence the susceptibility and severity of COVID-19, although the confidence of these findings is limited by a small number of studies and participants. Further studies are needed to address the potential role of VDR activation and DBP in the pathophysiology of COVID-19 which take into account the genetic variations of vitamin D metabolic pathway.

Assessing vitamin D metabolism - four decades of experience

One hundred years ago, the role of vitamin D for bone mineralization and the prevention of rickets was discovered. Vitamin D comprises a group of over 50 metabolites with multiple functions that go far beyond calcium homeostasis and bone mineralization. Approximately 50 years ago, first methods for the measurement of 25-hydroxyvitamin D (25(OH)D) in human blood were developed. Over the years, different analytical principals were employed including competitive protein binding assays, high-performance liquid chromatography, various immunoassay and mass spectrometric formats. Until the recent standardization of serum 25(OH)D measurement, agreement between methods was unsatisfactory. Since then, comparability has improved, but substantial variability between methods remains. With the advent of liquid chromatography tandem mass spectrometry (LC-MS/MS), the accurate determination of 25(OH)D and other metabolites, such as 24,25(OH)2D, becomes increasingly accessible for clinical laboratories. Easy access to 25(OH)D testing has triggered extensive clinical research showing that large parts of the population are vitamin D deficient. The variable response of vitamin D deficient individuals to supplementation indicates that assessing patients' vitamin D stores by measuring 25(OH)D provides limited insight into the metabolic situation. Meanwhile, first evidence has emerged suggesting that the simultaneous measurement of 25(OH)D, 24,25(OH)2D and other metabolites allows a dynamic evaluation of patients' vitamin D status on metabolic principals. This may help to identify patients with functional vitamin D deficiency from those without. It can be expected that research into the assessment vitamin D status will continue for another 50 years and that this will help rationalizing our approach in clinical practice.

Total, free, and bioavailable 25-hydroxyvitamin D levels in patients with periodontitis (stage III): a case-control study

OBJECTIVE

The aim of this study was to investigate the relationship between total, free and bioavailable 25-hydroxyvitamin D levels, and periodontitis.

MATERIALS AND METHODS

Thirty-nine patients with periodontitis diagnosis and 44 healthy participants were included in this study. 25-Hydroxyvitamin D, vitamin D-binding protein, procalcitonin, and albumin levels were measured from the serum samples obtained. Free and bioavailable 25-hydroxyvitamin D levels were calculated. Total, free, and bioavailable 25-hydroxyvitamin D levels were compared between the healthy control and periodontitis groups. The association of total 25 (OH)D levels with periodontitis was tested through univariate analysis and multivariate logistic regression.

RESULTS

Total 25-hydroxyvitamin D, bioavailable 25-hydroxyvitamin D, and free 25-hydroxyvitamin D levels were significantly lower in the periodontitis group than in the healthy control group (p < 0.001). In the logistic regression analysis, a significant correlation was observed between total 25-hydroxyvitamin D and periodontitis (p<0.001).

CONCLUSION

Our study shows that there is a relationship between total, free and bioavailable 25-hydroxyvitamin D levels and periodontitis. In addition, it has been shown that the determination of free and bioavailable 25-hydroxyvitamin D levels does not provide additional advantages in terms of the relationship between periodontitis and vitamin D.

CLINICAL RELEVANCE

In this case-control study, we examined the relationship between total, free and bioavailable 25-hydroxyvitamin D and periodontitis. We found lower total, free, and bioavailable 25-hydroxyvitamin D levels in periodontitis patients. It was also found that vitamin D-binding protein may be an important biomarker in the identification of various forms of periodontal disease.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier NCT05343273.

Associations between serum vitamin D biomarkers and tumor expression of Ki67, p53, and COX-2 in colorectal cancer cases from the Southern Community Cohort Study

Higher 25-hydroxyvitamin D is associated with lower colorectal cancer (CRC) risk, with limited data from African Americans (AAs), who have greater risk for CRC and 25-hydroxyvitamin D deficiency. In a predominantly AA sample of CRC cases from the Southern Community Cohort Study (SCCS), we report associations between vitamin D biomarkers and tumor expression of proteins implicated in vitamin D's anti-tumorigenic pathways (e.g. proliferation and inflammation) and CRC prognosis. SCCS participants with incident CRC were identified via state cancer registries. Serum 25-hydroxyvitamin D and vitamin D binding protein (VDBP) were measured at enrollment. 'Free' 25-hydroxyvitamin D was calculated via standard equation. Cellular Ki67, p53, and COX-2 were measured from tumor samples and categorized using literature-defined cut-points related to survival. Generalized linear models were used to measure associations between vitamin D exposures, tumor biomarkers, and stage. In total, 104 cases (40-79 years) were analyzed. 25-hydroxyvitamin D was not associated with high Ki67 (odds ratio (OR) per 1-standard deviation (SD) increase [95% confidence interval] 1.35[0.86-2.11]), p53 (0.75[0.47-1.20]), or COX-2 expression (1.25[0.78-2.01]), or metastatic disease (1.04[0.59-1.81]). Mean biomarker expression was unrelated to 25-hydroxyvitamin D (p-trend ≥.09). Null associations were observed for VDBP and free 25-hydroxyvitamin D. In AAs (n = 70), higher VDBP was associated with lower odds of high Ki67 expression (0.53[0.28-0.98], p-trend =.04). In conclusion, we observed no associations between 25-hydroxyvitamin D and prognostic marker expression in CRC. An inverse association between VDBP and tumor Ki67 in AAs is consistent with reports showing relationships with reduced CRC mortality.

Assessment of Vitamin D Status in Slovenian Premenopausal and Postmenopausal Women, Using Total, Free, and Bioavailable 25-Hydroxyvitamin D (25(OH)D)

The objective of our study was to evaluate vitamin D status and its predictors in Slovenian premenopausal and postmenopausal women. A cross-sectional study was carried out between 1 March 2021 and 31 May 2021. A total of 319 healthy women from the Central Slovenian region aged between 44 and 65 were recruited; 176 were included in the final analysis. The vitamin D status was determined by measuring the total 25-Hydroxycholecalciferol (25(OH)D) concentration, vitamin D binding protein (DBP), and albumin and calculating the bioavailable 25(OH)D and free 25(OH)D. For the calculation of bioavailable and free 25(OH)D, we developed a new online calculator. The Endocrine Society’s thresholds for vitamin D deficiency and insufficiency were used; 29.0% of premenopausal and 24.4% of postmenopausal subjects were found to be vitamin D deficient (total 25(OH)D < 50 nmol/L); 76.8% of the premenopausal and 61.7% of postmenopausal subjects were found to have insufficient levels (total 25(OH)D < 75 nmol/L). Premenopausal women had 11.8% lower total 25(OH)D, 32.2% lower bioavailable 25(OH)D, and 25.2% higher DBP than postmenopausal women. The most important predictors of vitamin D status were vitamin D supplementation and time spent in the sun. Contrary to similar studies, the vitamin D status in Slovenian postmenopausal women was significantly better than in premenopausal women. In postmenopausal women, the measurement of free or bioavailable 25(OH)D instead of the total 25(OH)D could be advantageous.

Role of Vitamin D in Celiac Disease and Inflammatory Bowel Diseases

Vitamin D (VD) is a pro-hormone that has long been known as a key regulator of calcium homeostasis and bone health in both children and adults. In recent years, studies have shown that VD may exert many extra-skeletal functions, mainly through a relevant modulation of the innate and adaptive immune system. This has suggested that VD could play a fundamental role in conditioning development, clinical course, and treatment of several autoimmune disorders, including celiac disease (CD) and inflammatory bowel diseases (IBDs). The main aim of this review is to evaluate the relationships between VD, CD, and IBDs. Literature analysis showed a potential impact of VD on CD and IBDs can be reasonably assumed based on the well-documented in vitro and in vivo VD activities on the gastrointestinal tract and the immune system. The evidence that VD can preserve intestinal mucosa from chemical and immunological damage and that VD modulation of the immune system functions can contrast the mechanisms that lead to the intestinal modifications characteristic of gastrointestinal autoimmune diseases has suggested that VD could play a role in controlling both the development and the course of CD and IBDs. Administration of VD in already diagnosed CD and IBD cases has not always significantly modified disease course. However, despite these relevant problems, most of the experts recommend monitoring of VD levels in patients with CD and IBDs and administration of supplements in patients with hypovitaminosis.

Vitamin D: sources, physiological role, biokinetics, deficiency, therapeutic use, toxicity, and overview of analytical methods for detection of vitamin D and its metabolites

Vitamin D has a well-known role in the calcium homeostasis associated with the maintenance of healthy bones. It increases the efficiency of the intestinal absorption of dietary calcium, reduces calcium losses in urine, and mobilizes calcium stored in the skeleton. However, vitamin D receptors are present ubiquitously in the human body and indeed, vitamin D has a plethora of non-calcemic functions. In contrast to most vitamins, sufficient vitamin D can be synthesized in human skin. However, its production can be markedly decreased due to factors such as clothing, sunscreens, intentional avoidance of the direct sunlight, or the high latitude of the residence. Indeed, more than one billion people worldwide are vitamin D deficient, and the deficiency is frequently undiagnosed. The chronic deficiency is not only associated with rickets/osteomalacia/osteoporosis but it is also linked to a higher risk of hypertension, type 1 diabetes, multiple sclerosis, or cancer. Supplementation of vitamin D may be hence beneficial, but the intake of vitamin D should be under the supervision of health professionals because overdosing leads to intoxication with severe health consequences. For monitoring vitamin D, several analytical methods are employed, and their advantages and disadvantages are discussed in detail in this review.

Nongenomic Activities of Vitamin D

Vitamin D shows a variety of pleiotropic activities which cannot be fully explained by the stimulation of classic pathway- and vitamin D receptor (VDR)-dependent transcriptional modulation. Thus, existence of rapid and nongenomic responses to vitamin D was suggested. An active form of vitamin D (calcitriol, 1,25(OH)₂D₃) is an essential regulator of calcium-phosphate homeostasis, and this process is tightly regulated by VDR genomic activity. However, it seems that early in evolution, the production of secosteroids (vitamin-D-like steroids) and their subsequent photodegradation served as a protective mechanism against ultraviolet radiation and oxidative stress. Consequently, direct cell-protective activities of vitamin D were proven. Furthermore, calcitriol triggers rapid calcium influx through epithelia and its uptake by a variety of cells. Subsequently, protein disulfide-isomerase A3 (PDIA3) was described as a membrane vitamin D receptor responsible for rapid nongenomic responses. Vitamin D was also found to stimulate a release of secondary massagers and modulate several intracellular processes-including cell cycle, proliferation, or immune responses-through wingless (WNT), sonic hedgehog (SSH), STAT1-3, or NF-kappaB pathways. Megalin and its coreceptor, cubilin, facilitate the import of vitamin D complex with vitamin-D-binding protein (DBP), and its involvement in rapid membrane responses was suggested. Vitamin D also directly and indirectly influences mitochondrial function, including fusion-fission, energy production, mitochondrial membrane potential, activity of ion channels, and apoptosis. Although mechanisms of the nongenomic responses to vitamin D are still not fully understood, in this review, their impact on physiology, pathology, and potential clinical applications will be discussed.

Host genetic diversity and genetic variations of SARS-CoV-2 in COVID-19 pathogenesis and the effectiveness of vaccination

The severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), responsible for the outbreak of coronavirus disease 2019 (COVID-19), has shown a vast range of clinical manifestations from asymptomatic to life-threatening symptoms. To figure out the cause of this heterogeneity, studies demonstrated the trace of genetic diversities whether in the hosts or the virus itself. With this regard, this review provides a comprehensive overview of how host genetic such as those related to the entry of the virus, the immune-related genes, gender-related genes, disease-related genes, and also host epigenetic could influence the severity of COVID-19. Besides, the mutations in the genome of SARS-CoV-2 __leading to emerging of new variants__ per se affect the affinity of the virus to the host cells and enhance the immune escape capacity. The current review discusses these variants and also the latest data about vaccination effectiveness facing the most important variants.

Decreased vitamin D-binding protein level portends poor outcome in acute-on-chronic liver failure caused by hepatitis B virus

BACKGROUND/AIMS

Acute-on-chronic liver failure (ACLF) is a catastrophic illness. Few studies investigated the prognostic value of vitamin D-binding protein (VDBP) for hepatitis B virus (HBV)-related ACLF (HBV-ACLF) resulted in conflicting results.

METHODS

Two prospective HBV-ACLF cohorts (n=287 and n=119) were enrolled to assess and validate the prognostic performance of VDBP.

RESULTS

VDBP levels in the non-survivors were significantly lower than in the survivors (P<0.001). Multivariate Cox regression demonstrated that VDBP was an independent prognostic factor for HBV-ACLF. The VDBP level at admission gradually decreased as the number of failed organs increased (P<0.001), and it was closely related to coagulation failure. The areas under the receiver operating characteristic curve (AUCs) of the Child-Pugh-VDBP and chronic liver failuresequential organ failure assessment (CLIF-SOFA)-VDBP scores were significantly higher than those of Child-Pugh (P<0.001) and CLIF-SOFA (P=0.0013). The AUCs of model for end-stage liver disease (MELD)-VDBP were significantly higher than those of MELD (P= 0.0384) only in the case of cirrhotic HBV-ACLF patients. Similar results were validated using an external multicenter HBV-ACLF cohort. By longitudinal observation, the VDBP levels gradually increased in survivors (P=0.026) and gradually decreased in non-survivors (P<0.001). Additionally, the VDBP levels were found to be significantly decreased in the deterioration group (P=0.012) and tended to be decreased in the fluctuation group (P=0.055). In contrast, they showed a significant increase in the improvement group (P=0.036).

CONCLUSION

The VDBP was a promising prognostic biomarker for HBV-ACLF. Sequential measurement of circulating VDBP shows value for the monitoring of ACLF progression.

Vitamin D-Binding Protein, Bioavailable, and Free 25(OH)D, and Mortality: A Systematic Review and Meta-Analysis

Introduction: Observational studies reported inverse associations between serum total 25-hydroxyvitamin D (25(OH)D) concentrations and mortality. Evolving evidence indicated, however, that bioavailable or free 25(OH)D may be even better predictors of mortality. We conducted a systematic review and meta-analysis to summarize the epidemiological evidence on associations of vitamin D-binding protein (VDBP), albumin-bound, bioavailable, and free 25(OH)D, with mortality. Methods: We systematically searched PubMed and Web of Science, up to 27 May 2022. Predictors of interest included serum or plasma concentrations of VDBP, albumin-bound, bioavailable, and free 25(OH)D. Assessed health outcomes were all-cause and cause-specific mortality. We included studies reporting associations between these biomarkers and mortality outcomes. We applied random-effects models for meta-analyses to summarize results from studies assessing the same vitamin D biomarkers and mortality outcomes. Results: We identified twelve eligible studies, including ten on VDBP, eight on bioavailable 25(OH)D, and eight on free 25(OH)D. No study reported on albumin-bound 25(OH)D and mortality. In meta-analyses, the highest levels of bioavailable and free 25(OH)D were associated with 37% (hazard ratio (HR): 0.63, 95% confidence interval (CI): 0.46, 0.87), and 29% (HR: 0.71, 95% CI: 0.53, 0.97) decrease in all-cause mortality, respectively, compared with the lowest levels. These estimates were similar to those for total 25(OH)D (HR: 0.67, 95% CI: 0.56, 0.80) observed in the same studies. Higher VDBP levels were associated with lower all-cause mortality in cancer patient cohorts. However, no such association was observed in general population cohorts. Conclusions: Similar inverse associations of total, bioavailable, and free 25(OH)D with mortality suggest that bioavailable and free 25(OH)D do not provide incremental value in predicting mortality.

Towards harmonization of directly measured free 25-hydroxyvitamin D using an enzyme-linked immunosorbent assay

The majority of circulating 25-hydroxyvitamin D (25(OH)D) is protein bound and perhaps less available than the free fraction of 25(OH)D; therefore, researchers have proposed that the measurement of free 25(OH)D in human serum may be a better indicator of vitamin D health status than total 25(OH)D. The availability of a new enzyme-linked immunosorbent assay (ELISA) for the determination of free 25(OH)D provides a method for direct measurement of the low levels of non-protein bound 25(OH)D. As an initial step towards harmonization of measurements of free 25(OH)D, the ELISA was used to measure free 25(OH)D in three existing Standard Reference Materials (SRMs): SRM 972a Vitamin D Metabolites in Frozen Human Serum, SRM 2973 Vitamin D Metabolites in Frozen Human Serum (High Level), and SRM 1949 Frozen Prenatal Human Serum. Target values for free 25(OH)D in the nine SRM serum pools, obtained by combining the results from two laboratories, ranged from 3.76 ± 0.36 to 10.0 ± 0.58 pg/mL. Of particular significance is the assignment of free 25(OH)D target values to SRM 1949, which consists of four serum pools from non-pregnant female donors of reproductive age and pregnant women in each of the three trimesters and which also has values assigned for vitamin D binding protein, which increases during pregnancy. The availability of target values for free 25(OH)D in these SRMs will allow researchers to validate new analytical methods and to compare their results with other researchers as an initial step towards harmonization of measurements among different studies and laboratories.

Vitamin D-binding protein, total, "nonbioavailable," bioavailable, and free 25-hydroxyvitamin D, and mortality in a large population-based cohort of older adults

BACKGROUND

Epidemiological studies consistently find low concentrations of 25-hydroxyvitamin D (25(OH)D) in blood to be associated with increased mortality, and a recent large-scale Mendelian randomization study strongly supports a causal relationship among individuals with low vitamin D status. Evolving evidence suggested that bioavailable or free 25(OH)D may better predict mortality. We aimed to compare the prognostic values of vitamin D-binding protein (VDBP), total, bioavailable, complementary "nonbioavailable", and free 25(OH)D for total and cause-specific mortality in a large population-based cohort study of older adults from Germany.

METHODS

Bioavailable, complementary "nonbioavailable", and free 25(OH)D concentrations were calculated among 5899 participants aged 50-75 years, based on serum concentrations of total 25(OH)D, VDBP, and albumin. The cohort was followed with respect to total and cause-specific mortality from recruitment in 2001-2002 up to the end of 2018. Multivariable Cox proportional hazards regression models were used to assess the associations between various vitamin D biomarkers and mortality, and further stratified by vitamin D status.

RESULTS

During a median follow-up of 17.1 years, 1739 participants died, of whom 575, 584, and 94 died of cardiovascular diseases, cancer, and respiratory diseases, respectively. Very similar inverse associations with total mortality (hazard ratio (HR) per standard deviation decrease: 1.17, 95% confidence interval (CI): 1.11, 1.24 for total 25(OH)D; HR: 1.14, 95% CI: 1.08, 1.21 for bioavailable 25(OH)D; HR: 1.12, 95% CI: 1.06, 1.18 for free 25(OH)D) and cause-specific mortalities were seen for all biomarkers of vitamin D status. The strongest associations were consistently seen for respiratory mortality. These inverse associations were strongest among participants with low vitamin D levels (<50 nmol/L). No significant associations were seen between VDBP and mortality.

CONCLUSIONS

Total, nonbioavailable, bioavailable, and free 25(OH)D showed very similar inverse associations with total and cause-specific mortality, which were strongest among those with low vitamin D status in this large population-based cohort.

Vitamin D: a potentially important secosteroid for coping with COVID-19

COVID-19 is a disease that has caused a high number of deaths in the world, and despite being controlled, it requires attention and the search for new quick and economical therapeutic strategies. In this sense, vitamin D stands out, an immunomodulator that has shown beneficial effects in decreasing the risk and severity of acute respiratory tract infections, including COVID-19. Therefore, this review presents a number of experimental, observational and clinical studies on the importance of vitamin D against viral infections with an emphasis on COVID-19, highlighting the relationship between vitamin D, Renin-Angiotensin System and cytokine storms with decreased inflammatory lesions in patients with COVID-19. In addition, aspects of pathophysiology, metabolism, risk factors, sources and recommendations of vitamin D are described. We conclude that vitamin D plays a protective role against inflammatory lesions and can decrease the risk of infections and the severity of COVID-19. Therefore, it is essential to maintain adequate levels of vitamin D to avoid complications related to its deficiency.

Differing effects of oral conjugated equine estrogen and transdermal estradiol on vitamin D metabolism in postmenopausal women: a 4-year longitudinal study

OBJECTIVE

The aim of this study was to examine the effect of either conjugated equine estrogen or transdermal estradiol on vitamin D metabolism in postmenopausal women.

METHODS

Twenty-five women from the Kronos Early Estrogen Prevention Study who were randomized to conjugated equine estrogen 0.45 mg/d and 20 women who were treated with transdermal estradiol 50 mg/d (patch replaced weekly) were analyzed in the present study. All participants received micronized progesterone for 12 days per month.

RESULTS

There was no significant treatment effect on serum total 25-hydroxyvitamin D over 48 months in either study group, and there were no significant differences between treatment arms. In contrast, at 12 months, directly measured free 25-hydroxyvitamin D was significantly higher in the transdermal estradiol group than in the conjugated equine estrogen group. Directly measured free 25-hydroxyvitamin D subsequently increased significantly from 12 to 48 months in both treatment arms. Calculated free 25-hydroxyvitamin D was also significantly higher in the transdermal estradiol group at 36 months. Vitamin D-binding protein decreased significantly in both treatment groups from 12 to 48 months, but at 48 months, least square mean values were no different based on treatment assignment.

CONCLUSIONS

Directly measured free 25-hydroxyvitamin D levels, but not serum total 25-hydroxyvitamin D levels, are different within the first 12 months of estrogen replacement depending on the preparation. However, this difference is transient, in that there were no differences at 36 or 48 months. These findings suggest that there may be a short-term benefit to prescribing transdermal estradiol for women who are either vitamin D deficient or vitamin D insufficient.

Serum Vitamin D Levels Explored in the Latvian Cohort of Patients with Basal Cell Carcinoma Linked to the Sonic Hedgehog and Vitamin D Binding Protein Cutaneous Tissue Indices

Ultraviolet radiation is known as one of the major contributors to skin malignancies, including basal cell carcinoma (BCC), which is the most common type of skin cancer. It is a heterogeneous tumor, which presents with various types that are stratified into low- and high-risk tumors. Sunlight is important for overall health and vitamin D synthesis in the skin, whereas deviations from the optimal level of vitamin D are shown to be associated with the risk of the development of BCC. The accumulating evidence suggests the ability of vitamin D to antagonize the Sonic Hedgehog (SHH) signaling, the key tumor pathway, and play a protective role in the development of BCC. Additionally, a vitamin D binding protein (DBP) is shown to be implicated in the complex regulation of vitamin D. Here, we aimed to explore serum vitamin D in patients with different primary and recurrent BCC of the head and neck and investigate cutaneous DBP and SHH indices, confirmed immunohistochemically in these subjects. According to the results, 94.9% of the Latvian cohort of BCC patients were found to be deficient in vitamin D. No significant differences in serum vitamin D levels were found between genders, primary and recurrent tumors, and different types of BCC. Serum vitamin D was inversely associated with tumor size. Susceptible male individuals with low blood vitamin D levels were recognized at risk of developing aggressive and recurrent BCC confirmed by the use of hierarchical clustering analysis. In smaller tumors with a favorable course, such as superficial and nodular BCC, the association between high DBP and low SHH tissue expression was found, providing supportive evidence of the existence of a link between vitamin D, proteins involved in its metabolism, as exemplified by the DBP and SHH signaling pathway. The assumption of a deficiency in the protective effect of vitamin D in patients with high-risk BCCs was proposed in low DBP and high SHH tissue indices. New extensions to existing knowledge and characterization of the BCC signaling pathways and their cross-talk with vitamin D are warranted when searching for a preferential effect of vitamin D on skin cancer.

Consistent Inverse Associations of Total, “Bioavailable”, Free, and “Non-Bioavailable” Vitamin D with Incidence of Diabetes among Older Adults with Lower Baseline HbA1c (≤6%) Levels

Background: Serum 25-hydroxyvitamin (25(OH)D) levels are inversely associated with risk of diabetes. The “free hormone hypothesis” suggests potential effects to be mainly related to concentrations of “bioavailable” and free rather than total 25(OH)D. We assessed associations of serum concentrations of vitamin D-binding protein (VDBP), as well as total “bioavailable”, complementary “non-bioavailable”, and free 25(OH)D, with the risk of developing diabetes among non-diabetic older adults in a large population-based cohort study in Germany. Methods: We included 4841 non-diabetic older adults aged 50–75 years at the baseline exam from the ESTHER cohort conducted in Saarland, Germany, in 2001–2002. Concentrations of “bioavailable” and free 25(OH)D were derived from serum concentrations of VDBP, total 25(OH)D, and albumin. Incidence of diabetes was ascertained during up to 14 years of follow-up. Associations were quantified by multivariable Cox proportional hazards regression models with comprehensive confounder adjustment. Results: During a median follow-up of 10.6 years, 837 non-diabetic participants developed diabetes. We observed similar inverse associations with developing diabetes for VDBP (hazard ratio (HR) for lowest versus highest quintile: 1.37, 95% confidence interval (CI): 1.09, 1.72), total 25(OH)D (HR: 1.31, 95% CI: 1.03, 1.66), and “non-bioavailable” 25(OH)D (HR: 1.30, 95% CI: 1.02, 1.65). Associations were smaller and statistically insignificant for “bioavailable” and free 25(OH)D. However, associations of total “non-bioavailable”, “bioavailable”, and free 25(OH)D with incidence of diabetes were much stronger among, and essentially restricted to, participants with lower baseline HbA_1c (≤6%) levels. Conclusions: This large prospective cohort study of older Caucasian adults, in agreement with results from randomized trials and Mendelian randomization studies, supports a protective effect of vitamin D against development of diabetes. The “free hormone theory” may not be relevant in this context. However, our results underline the importance of adequate vitamin D status among those who have not yet shown any sign of impaired glucose tolerance.

Bibliometric analysis of the global research status and trends of the association between Vitamin D and infections from 2001 to 2021

Objective

The objective of this study was the visualization of hot spots and evolving trends in research on the association between vitamin D and infections through the use of bibliometric analysis.

Methods

Based on 3046 relevant articles collected in the Web of Science Core Collection for the period of 2001–2021, the data were processed using CiteSpace software. GraphPad software was used for some of the graphics.

Results

A total of 3,046 literature were retrieved, with an average citation frequency of 27.89 times. The number of published papers in the direction of “Immunology” (453 articles, 14.9%) and “Infectious diseases” (312 articles, 10.2%) is much higher. The United States presents the highest publication count (890, 29.2%) and shows a strong leadership in this field. Country burst shows that since 2015, many developing countries and low-income countries have carried out enthusiastic research in this regard, including China, Pakistan, and Iran. As for institutions, the League of European Research Universities produces a larger proportion of articles (220, 7.2%). In terms of authors, Martineau AR and Camargo CA have the highest number of published articles, contributing 30 (0.99%) and 28 articles (0.92%), respectively. Major studies are supported by the United States Department of Health Human Services funding (394, 12.9%). According to the keyword co-occurrence diagram, the 10 most frequent keywords from 2001 to 2021 are “vitamin D”, “infection”, “d deficiency”, “risk”, “association”, “expression”, “disease”, “d supplementation”, “vitamin d deficiency”, and “children”. The top 10 cited articles in 2021 are all related to COVID-19, suggesting it is a hotspot in recent times.

Conclusion

Research on the association between vitamin D and infection has grown rapidly since 2012 and is generally developing well. While developed Western countries continue to be leading roles in this field, research trends in developing countries are also very promising. It is demonstrated that the relationship between vitamin D and respiratory infections, especially respiratory viruses and the more recently COVID-19, has received a lot of attention in the last two decades, suggesting that this is the hotspot and frontier of research issue.

Rapidly Increasing Serum 25(OH)D Boosts the Immune System, against Infections-Sepsis and COVID-19

Vitamin D deficiency is a global public health problem, a pandemic that commonly affects the elderly and those with comorbidities such as obesity, diabetes, hypertension, respiratory disorders, recurrent infections, immune deficiency, and malignancies, as well as ethnic minorities living in temperate countries. The same groups were worst affected by COVID-19. Since vitamin D deficiency weakens the immune system, it increases the risk of infections, complications, and deaths, such as from sepsis and COVID-19. Deficiency can be remedied cost-effectively through targeted food fortification, supplementation, and/or daily safe sun exposure. Its endocrine functions are limited to mineral metabolism, musculoskeletal systems, specific cell membrane interactions, and parathyroid gland functions. Except for the rapid, endocrine, and cell membrane-based non-genomic functions, all other biological and physiological activities of vitamin D depend on the adequate intracellular synthesis of 1,25(OH)2D (calcitriol) in peripheral target cells via the genome. Calcitriol mediates autocrine (intracrine) and paracrine signalling in immune cells, which provides broader, protective immune functions crucial to overcoming infections. The synthesis of 1,25(OH)2D (calcitriol) in peripheral target cells is dependent on diffusion and endocytosis of D3 and 25(OH)D from the circulation into them, which requires maintenance of serum 25(OH)D concentration above 50 ng/mL. Therefore, in acute infections such as sepsis and respiratory infections like COVID-19, it is necessary to rapidly provide its precursors, D3 and 25(OH)D, through the circulation to generate adequate intracellular calcitriol. Immune defence is one of the crucial non-hormonal functions of vitamin D. A single oral (bolus) dose or divided upfront loading doses between 100,000 and 500,000 IU, using 50,000 IU vitamin D3 increase the serum 25(OH)D concentrations to a therapeutic level of above 50 ng/mL that lasts between two to three months. This takes three to five days to raise serum 25(OH)D. In contrast, a single oral dose of calcifediol (0.014 mg/kg body weight) can generate the needed 25(OH)D concentration within four hours. Considering both D3 and 25(OH)D enter immune cells for generating calcitriol, using the combination of D3 (medium-term) and calcifediol (immediate) is cost-effective and leads to the best clinical outcome. To maximise protection against infections, particularly to reduce COVID-19-associated complications and deaths, healthcare workers should advise patients on safe sun exposure, adequate vitamin D supplementation and balanced diets containing zinc, magnesium, and other micronutrients to support the immune system. Meanwhile, governments, the World Health Organisation, the Centers for Disease Control, and governments should consider similar recommendations to physicians and the public, change the outdated vitamin D and other micronutrient recommendations directed to their population, and organise targetted food fortification programs for the vulnerable groups. This article discusses a rational approach to maintaining a sustained serum 25(OH)D concentration above 50 ng/mL, necessary to attain a robust immune system for overcoming infections. Such would cost-effectively improve the population’s health and reduce healthcare costs. It also describes three cost-effective, straightforward protocols for achieving and sustaining therapeutic serum 25(OH)D concentrations above 50 ng/mL (>125 nmol/L) to keep the population healthy, reduce absenteeism, improve productivity, and lower healthcare costs.

Relationship Between Metabolites of Vitamin D, Free 25-(OH)D, and Physical Performance in Indoor and Outdoor Athletes

The potential effects of vitamin D in athletes have received considerable attention in the literature. However, little is known about vitamin D metabolites and their association with physical performance in athletes. Therefore, the aim of our study was to determine the relationship between metabolites of vitamin D, vitamin D binding protein (VDBP), free, bioavailable 25-(OH)D, and physical fitness tests in athletes. A total of 40 indoor and outdoor players (16 judoists and 24 football players) participated in the study. Vitamin D metabolites (25-(OH)D, 24,25-(OH)₂D₃, 3-epi-25-(OH)D₃, and 1,25-(OH)₂D) were assessed using LM-MS/MS. Free 25-(OH)D concentration was evaluated by calculation using serum albumin and VDBP levels. Athletic performance was assessed using handgrip and vertical jump. Our study showed a significant correlation between vitamin D metabolites and handgrip strength and vertical jump variables in indoor players. It demonstrated a significant association between 3-epi-25-(OH)D₃ and vertical jump parameters in outdoor players. The results of our study showed relationship between free, bioavailable 25-(OH)D, and vertical jump variables in indoor players. In conclusion, we provide novel information on the vitamin D metabolites and athletic performance in athletes. Based on the results of our study, we concluded that vitamin D metabolites might be involved in skeletal muscle function in relation to athletic performance.

Interactions between Vitamin D Genetic Risk and Dietary Factors on Metabolic Disease-Related Outcomes in Ghanaian Adults

The Ghanaian population is experiencing an upsurge in obesity and type 2 diabetes (T2D) due to rapid urbanization. Besides dietary factors, vitamin D-related genetic determinants have also been shown to contribute to the development of obesity and T2D. Hence, we aimed to examine the interactions between dietary factors and vitamin D-related genetic variants on obesity and T2D related outcomes in a Ghanaian population. Three hundred and two healthy Ghanaian adults (25-60 years old) from Oforikrom, Municipality in Kumasi, Ghana were randomly recruited and had genetic tests, dietary consumption analysis, and anthropometric and biochemical measurements of glucose, HbA1c, insulin, cholesterol, and triglycerides taken. A significant interaction was identified between vitamin D-GRS and fiber intake (g/day) on BMI (pinteraction = 0.020) where those who were consuming low fiber (≤16.19 g/d) and carrying more than two risk alleles for vitamin D deficiency (p = 0.01) had a significantly higher BMI. In addition, an interaction between vitamin D-GRS and fat intake (g/day) on HbA1c (total fat, pinteraction = 0.029) was found, where participants who had a lower total fat intake (≤36.5 g/d), despite carrying more than two risk alleles, had significantly lower HbA1c (p = 0.049). In summary, our study has identified novel gene-diet interactions of vitamin D-GRS with dietary fiber and fat intakes on metabolic traits in Ghanaian adults.

Predictors of progression from a first demyelinating event to clinically definite multiple sclerosis

Understanding the predictors of progression from a first to a second demyelinating event (and formerly, a diagnosis of clinically definite multiple sclerosis) is important clinically. Previous studies have focused on predictors within a single domain, e.g. radiological, lacking prospective data across multiple domains. We tested a comprehensive set of personal, environmental, neurological, MRI and genetic characteristics, considered together, as predictors of progression from a first demyelinating event to clinically definite multiple sclerosis. Participants were aged 18–59 years and had a first demyelinating event during the study recruitment period (1 November 2003–31 December 2006) for the Ausimmune Study (n = 216) and had follow-up data to 2–3 years post-initial interview. Detailed baseline data were available on a broad range of demographic and environmental factors, MRI, and genetic and viral studies. Follow-up data included confirmation of clinically definite multiple sclerosis (or not) and changes in environmental exposures during the follow-up period. We used multivariable logistic regression and Cox proportional hazards regression modelling to test predictors of, and time to, conversion to clinically definite multiple sclerosis. On review, one participant had an undiagnosed event prior to study recruitment and was excluded (n = 215). Data on progression to clinically definite multiple sclerosis were available for 91.2% (n = 196); 77% were diagnosed as clinically definite multiple sclerosis at follow-up. Mean (standard deviation) duration of follow-up was 2.7 (0.7) years. The set of predictors retained in the best predictive model for progression from a first demyelinating event to clinically definite multiple sclerosis were as follows: younger age at first demyelinating event [adjusted odds ratio (aOR) = 0.92, 95% confidence interval (CI) = 0.87–0.97, per additional year of age); being a smoker at baseline (versus not) (aOR = 2.55, 95% CI 0.85–7.69); lower sun exposure at age 6–18 years (aOR = 0.86, 95% CI 0.74–1.00, per 100 kJ/m² increment in ultraviolet radiation dose), presence (versus absence) of infratentorial lesions on baseline magnetic resonance imaging (aOR = 7.41, 95% CI 2.08–26.41); and single nucleotide polymorphisms in human leukocyte antigen (HLA)-B (rs2523393, aOR = 0.25, 95% CI 0.09–0.68, for any G versus A:A), TNFRSF1A (rs1800693, aOR = 5.82, 95% CI 2.10–16.12, for any C versus T:T), and a vitamin D-binding protein gene (rs7041, aOR = 3.76, 95% CI 1.41–9.99, for any A versus C:C). The final model explained 36% of the variance. Predictors of more rapid progression to clinically definite multiple sclerosis (Cox proportional hazards regression) were similar. Genetic and magnetic resonance imaging characteristics as well as demographic and environmental factors predicted progression, and more rapid progression, from a first demyelinating event to a second event and clinically definite multiple sclerosis.

Serum 25-hydroxyvitamin D Concentration Significantly Decreases in Patients with COVID-19 Pneumonia during the First 48 Hours after Hospital Admission

It is unclear how ongoing inflammation in Coronavirus Disease 2019 (COVID-19) affects 25-hydroxyvitamin D (25[OH]D) concentration. The objective of our study was to examine serum 25(OH)D levels during COVID-19 pneumonia. Patients were admitted between 1 November and 31 December 2021. Blood samples were taken on admission (day 0) and every 24 h for the subsequent four days (day 1−4). On admission, 59% of patients were 25(OH)D sufficient (>30 ng/mL), and 41% had 25(OH)D inadequacy (<30 ng/mL). A significant fall in mean 25(OH)D concentration from admission to day 2 (first 48 h) was observed (30.7 ng/mL vs. 26.4 ng/mL; p < 0.0001). No subsequent significant change in 25(OH)D concentration was observed between day 2 and 3 (26.4 ng/mL vs. 25.9 ng/mL; p = 0.230) and day 3 and day 4 (25.8 ng/mL vs. 25.9 ng/mL; p = 0.703). The absolute 25(OH)D change between hospital admission and day 4 was 16% (4.8 ng/mL; p < 0.0001). On day 4, the number of patients with 25(OH)D inadequacy increased by 18% (p = 0.018). Therefore, serum 25(OH)D concentration after hospital admission in acutely ill COVID-19 patients should be interpreted with caution. Whether low 25(OH)D in COVID-19 reflects tissue level vitamin D deficiency or represents only a laboratory phenomenon remains to be elucidated in further prospective trials of vitamin D supplementation.

Free Vitamin D3 Index and Vitamin D-binding protein in multiple sclerosis - a presymptomatic case-control study

Background and purpose

High levels of 25‐hydroxyvitamin D₃ (25[OH]D₃) are associated with a lower risk for multiple sclerosis (MS). The bioavailability of 25(OH)D₃ is regulated by its main plasma carrier, vitamin D‐binding protein (DBP). Free 25(OH)D₃ can be estimated by also measuring DBP concentration. In addition, DBP has immunomodulatory functions that may independently affect MS pathogenesis. No previous studies have assessed free 25(OH)D₃ or DBP in presymptomatically collected samples. This study was undertaken to assess free 25(OH)D₃ and DBP as risk factors for MS.

Methods

A nested case–control study was performed with presymptomatic serum samples identified through cross‐linkage of MS registries and Swedish biobanks. Concentration of 25(OH)D₃ was measured with liquid chromatography and DBP levels with sandwich immunoassay. Free 25(OH)D₃ was approximated as free vitamin D₃ index: (25[OH]D₃/DBP) × 10³. MS risk was analyzed by conditional logistic regression, calculating odds ratios (ORs) with 95% confidence intervals (CIs).

Results

Serum samples from 660 pairs of matched cases and controls were included.

At <20 years of age, high levels of free vitamin D₃ index were associated with a lower risk of MS (highest vs. lowest quintile: OR = 0.37, 95% CI = 0.15–0.91, p for trend across quintiles = 0.04). At age 30–39 years, high levels of DBP were associated with a lower MS risk (highest vs. lowest quintile: OR = 0.36, 95% CI = 0.15–0.85, p for trend = 0.02).

Conclusions

These findings support the hypothesis that high levels of free 25(OH)D₃ at a young age reduce the risk of MS later in life. They also implicate a role for DBP in MS etiology.

The association of free vitamin D₃ index, vitamin D‐binding protein, and the risk of developing multiple sclerosis was assessed in a case–control study of presymptomatically collected samples. High free vitamin D₃ index before the age of 20 years was associated with a lower risk of developing multiple sclerosis later in life. High levels of vitamin D binding protein after the age of 30 years were associated with a lower risk of developing multiple sclerosis.

Vitamin D Status Assessment: Lack of Correlation between Serum and Hair 25-Hydroxycholecalciferol Levels in Healthy Young Adults

Vitamin D deficiency has been linked to numerous health problems, including those resulting from disturbed calcium-phosphorus homeostasis, and neuropsychiatric and autoimmune disorders. Nearly one-third of the global population has suboptimal levels of vitamin D, according to epidemiological data. Vitamin D status is usually determined by measuring serum 25(OH)D, but, for decades, serum 25(OH)D measurement has been hampered by a lack of standardization. There have been many recent initiatives to develop reference substances and methods for measuring vitamin D and its metabolites, and re-evaluating the optimal values. It was also suggested that alternative biological samples could also be used, such as hair, since it has been established that lipophilic substances, such as corticosteroids, can also be found in hair. The purpose of this study was to determine the correlation between 25(OH)D3 concentrations in serum and hair, and other demographic features in 26 healthy Caucasian young adult volunteers. The determination of 25(OH)D3 and cholecalciferol was carried out using liquid chromatography coupled with mass spectrometry (LC-MS) from blood and hair samples taken at two timepoints separated by nine weeks. In the hair samples of 18 out of 26 subjects, 25(OH)D was detected at a mean (±SEM) concentration of 17.07 ± 5.375 pg/mg at the first sampling time, and 58.90 ± 25.97 pg/mg at the second sampling time. A multiple linear regression analysis revealed no effects of gender, body mass index, supplementation, or sun exposure on hair 25(OH)D3 concentrations, but supplementation and sun exposure significantly increased serum 25(OH)D3 concentrations. In addition, serum and hair 25(OH)D3 concentrations did not correlate; however, there was a strong correlation between the two sampling times for serum 25(OH)D3 concentrations. In conclusion, this study confirmed that 25(OH)D3 could be detected in human hair, but its use as a biomarker warrants further investigations since no link was found between serum 25(OH)D3 concentrations, supplementation, sun exposure, and hair 25(OH)D3 concentrations levels.

Perspectives: on Precision Nutrition Research in Heart, Lung, and Blood Diseases and Sleep Disorders

The release of the 2020-2030 Strategic Plan for NIH Nutrition Research (SPNR) and its emphasis on precision nutrition has provided an opportunity to identify future nutrition research that addresses individual variability in response to diet and nutrition across the life span-including those relevant to the Strategic Vision of the National Heart, Lung, and Blood Institute (NHLBI). The SPNR and the NHLBI's Strategic Vision were developed with extensive input from the extramural research community, and both have 4 overarching strategic goals within which are embedded several objectives for research. For the SPNR, these include 1) spur discovery science and normal biological functions (e.g., role of the microbiome in health and disease), 2) population science to understand individual differences (e.g., biomarkers including 'omics that predict disease status), 3) emerging scientific areas of investigation and their application (e.g., data science, artificial intelligence), and 4) cross-cutting themes (e.g., training the scientific workforce and minority health and health disparities). These strategic goals and objectives serve as blueprints for research and training. Nutrition remains important in the prevention and treatment of heart, lung, blood, and sleep (HLBS) disorders and diseases, and the NHLBI has played a pivotal role in supporting nutrition research. In this paper, we report important gaps in the scientific literature related to precision nutrition in HLBS diseases. Research opportunities that could stimulate precision nutrition and their alignment with the SPNR and the NHLBI Strategic Vision Objectives are provided. These opportunities include 1) exploring individual differences in response to varying dietary patterns and nutrients; 2) investigating genetic/epigenetic, biological (e.g., microbiome, biomarkers), social, psychosocial, and environmental underpinnings of individual variability in diet; 3) elucidating the role of circadian rhythm and chrononutrition; and 4) applying implementation science research methods in precision nutrition interventions relevant to HLBS diseases.

Vitamin D, vitamin D-binding protein, free vitamin D and COVID-19 mortality in hospitalized patients

BACKGROUND

Vitamin D deficiency has been associated with worse coronavirus disease 2019 (COVID-19) outcomes, but circulating 25-hydroxyvitamin D [25(OH)D] is largely bound to vitamin D-binding protein (DBP) or albumin, both of which tend to fall in illness, making the 25(OH)D status hard to interpret. Because of this, measurements of unbound ("free") and albumin-bound ("bioavailable") 25(OH)D have been proposed.

OBJECTIVES

We aimed to examine the relationship between vitamin D status and mortality from COVID-19.

METHODS

In this observational study conducted in Liverpool, UK, hospitalized COVID-19 patients with surplus sera available for 25(OH)D analysis were studied. Clinical data, including age, ethnicity, and comorbidities, were extracted from case notes. Serum 25(OH)D, DBP, and albumin concentrations were measured. Free and bioavailable 25(OH)D were calculated. Relationships between total, free, and bioavailable 25(OH)D and 28-day mortality were analyzed by logistic regression.

RESULTS

There were 472 patients with COVID-19 included, of whom 112 (23.7%) died within 28 days. Nonsurvivors were older (mean age, 73 years; range, 34-98 years) than survivors (mean age, 65 years; range, 19-95 years; P = 0.003) and were more likely to be male (67%; P = 0.02). The frequency of vitamin D deficiency [25(OH)D < 50 nmol/L] was similar between nonsurvivors (71/112; 63.4%) and survivors (204/360; 56.7%; P = 0.15) but, after adjustments for age, sex, and comorbidities, increased odds for mortality were present in those with severe deficiency [25(OH)D < 25 nmol/L: OR, 2.37; 95% CI, 1.17-4.78] or a high 25(OH)D (≥100 nmol/L; OR, 4.65; 95% CI, 1.51-14.34) compared with a 25(OH)D value of 50-74 nmol/L (reference). Serum DBP levels were not associated with mortality after adjustments for 25(OH)D, age, sex, and comorbidities. Neither free nor bioavailable 25(OH)D values were associated with mortality.

CONCLUSIONS

Vitamin D deficiency, as commonly defined by serum 25(OH)D levels (<50 nmol/L), is not associated with increased mortality from COVID-19, but extremely low (<25 nmol/L) and high (>100 nmol/L) levels may be associated with mortality risks. Neither free nor bioavailable 25(OH)D values are associated with mortality risk. The study protocol was approved by the London-Surrey Research Ethics Committee (20/HRA/2282).

Analytical, experimental and clinical aspects of total 25-hydroxyvitamin D measurement by two ligand assays are differentially biased by disease-related factors

BACKGROUND

Pathological concentrations of plasma proteins may confound the results of binding assays. We compared two routinely used total 25-hydroxyvitamin D [t-25(OH)D] methods: a chemiluminescence-immuno-(CLIA) and an electro-chemiluminescence-protein-binding-(ECLPBA) assay.

METHODS

Two sub-studies were performed: 1) In an "in vitro" study, exogenous albumin was added to pools of patients' sera with low albumin levels; and 2) In "ex vivo" studies of Cohort_1: sera of hospitalized patients with low albumin levels, and of healthy controls; and of Cohort_2: outpatients with chronic kidney disease in pre-dialysis stage, or on peritoneal dialysis and hemodialysis were investigated by the routine and LC_MS/MS methods.

RESULTS

When increasing albumin concentrations were "in vitro" added, t-25(OH)D levels were overestimated by ECLPBA, and underestimated by CLIA. In patients' sera, positive correlations were detected between t-25(OH)D-vitamin D binding protein (DBP) values by both routine methods, and between t-25(OH)D-albumin values by all three methods. Much higher t-25(OH)D was measured by LC_MS/MS in all subgroups. When altering albumin levels with constant DBP concentration, the "in vitro" experiment revealed a higher sensitivity of ECLPBA. The "ex vivo" measurements demonstrated clinically relevant differences between the routine methods.

CONCLUSION

Both routine methods are dependent of the matrix effect in hospitalized patients, which is predicted by the DBP/Albumin ratios. In hemodialysis, ECLPBA is recommended because its outcomes differ less from those of LC_MS/MS. The results of LC_MS/MS are reliable, but not routinely available. A guidance would be valuable on how levels measured by the binding methods differ from those by LC-MS/MS in various clinical conditions.

Vitamin D metabolites and risk of first clinical diagnosis of central nervous system demyelination

Low 25-hydroxyvitamin D (25(OH)D) concentration is a recognised risk factor for multiple sclerosis (MS). Associations with vitamin D metabolites and vitamin D binding globulin (VDBG) have not been widely studied. We assessed the association between vitamin D metabolites (25(OH)D₂, 25(OH)D₃, c3-epimer 25(OH)D₃, 1,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃), and 24,25-dihydroxyvitamin D₃ (24,25(OH)₂D₃)) measured by liquid chromatography-tandem mass spectrometry assays, VDBG measured using a polyclonal immunoassay, and calculated free and bioavailable 25(OH)D, free 1,25(OH)₂D₃, and the 24,25(OH)₂D₃: total 25(OH)D and total 1,25(OH)₂D: total 25(OH)D ratios with risk of a first clinical diagnosis of CNS demyelination (FCD) in an Australian case-control study (n = 196 cases, n = 241 controls, matched on age, sex and study region). Higher 25(OH)D (adjusted odds ratio (AOR) = 0.94 (95 % confidence interval (CI) 0.85-1.03) per 10 nmol/L increment) and 24,25(OH)₂D₃ (AOR = 0.81 (95 %CI 0.65-1.00) per 1 nmol/L increment) concentrations were associated with reduced FCD risk. Our results were compatible with no association for the other vitamin D metabolites, ratios, or VDBG with FCD risk. Thus, using standardised assays, and a comprehensive range of vitamin D metabolites, we confirmed the association of higher 25(OH)D and reduced FCD risk, and describe a similar effect for 24,25(OH)₂D₃; free or bioavailable 25(OH)D were not associated with FCD risk.

Vitamin D in dairy cows: metabolism, status and functions in the immune system

The function of vitamin D in calcium homoeostasis in dairy cows, such as in other vertebrates, is known for many years. In recent years, new and interesting, non-classical functions of vitamin D have been elucidated, including effects on the immune system. The major aim of this review is to provide an overview of effects of vitamin D or its metabolites on the immune system in dairy cows. The first part of the review provides an overview of vitamin D metabolism, with particular reference to the role of various proteins (25- and 1-hydroxylases, vitamin D binding protein, vitamin D receptor) in vitamin D signalling. The second part deals with the role of the concentration of 25-hydroxyvitamin D [25(OH)D] in plasma as an indicator of the vitamin D status in dairy cows, and its dependence on sunlight exposure and dietary vitamin D supplementation. In this part also the "free hormone hypothesis" is discussed, indicating that the concentration of free 25(OH)D might be a more valid indicator of the vitamin D status than the concentration of total 25(OH)D. The third part deals with classical and the non-classical functions of vitamin D. Among the non-classical functions which are based on an autocrine vitamin D signalling, particular reference is given to the effects of vitamin D and vitamin D metabolites on the immune system in bovine immune cells and in dairy cows. Recent findings provide some indication that vitamin D or its metabolite 25(OH)D could enhance the immune function in dairy cows and be useful for the prevention and therapy of mastitis. However, the number of studies reported so far in this respect is very limited. Thus, much more research is required to yield clear concepts for an optimised usage of vitamin D to improve the immune system and prevent infectious diseases in dairy cows.

Cystic fibrosis related liver disease and endocrine considerations

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Development of CFLD adds significant morbidity and mortality to those with CF.

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CFLD is associated with an increased prevalence of endocrinopathies.

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Current treatment options for CFLD remain limited.

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Early recognition and treatment of CFLD associated conditions is critical.

Cystic fibrosis-liver disease (CFLD) is one of the most common non-pulmonary complications in the CF population, is associated with significant morbidity and represents the third leading cause of mortality in those with CF. CFLD encompasses a broad spectrum of hepatobiliary manifestations ranging from mild transaminitis, biliary disease, hepatic steatosis, focal biliary cirrhosis and multilobular biliary cirrhosis. The diagnosis of CFLD and prediction of disease progression remains a clinical challenge. The identification of novel CFLD biomarkers as well as the role of newer imaging techniques such as elastography to allow for early detection and intervention are active areas of research focus. Biliary cirrhosis with portal hypertension represents the most severe spectrum of CFLD, almost exclusively develops in the pediatric population, and is associated with a decline in pulmonary function, poor nutritional status, and greater risk of hospitalization. Furthermore, those with CFLD are at increased risk for vitamin deficiencies and endocrinopathies including CF-related diabetes, CF-related bone disease and hypogonadism, which can have further implications on disease outcomes and management. Effective treatment for CFLD remains limited and current interventions focus on optimization of nutritional status, identification and treatment of comorbid conditions, as well as early detection and management of CFLD specific sequelae such as portal hypertension or variceal bleeding. The extent to which highly effective modulator therapies may prevent the development or modify the progression of CFLD remains an active area of research. In this review, we discuss the challenges with defining and evaluating CFLD and the endocrine considerations and current management of CFLD.

Association of Vitamin D Status and COVID-19-Related Hospitalization and Mortality

BACKGROUND

The relationship between vitamin D status and COVID-19-related clinical outcomes is controversial. Prior studies have been conducted in smaller, single-site, or homogeneous populations limiting adjustments for social determinants of health (race/ethnicity and poverty) common to both vitamin D deficiency and COVID-19 outcomes.

OBJECTIVE

To evaluate the dose-response relationship between continuous 25(OH)D and risk for COVID-19-related hospitalization and mortality after adjusting for covariates associated with both vitamin D deficiency and COVID-19 outcomes.

DESIGN

Retrospective cohort study.

PATIENTS

Veteran patients receiving care in US Department of Veteran Affairs (VA) health care facilities with a positive severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) test and a blood 25(OH)D test between February 20, 2020, and November 8, 2020, followed for up to 60 days.

MAIN MEASURES

Exposure was blood 25(OH)D concentration ascertained closest to and within 15 to 90 days preceding an index positive SARS-CoV-2 test. Co-primary study outcomes were COVID-19-related inpatient hospitalization requiring airborne, droplet, contact, or other isolation and mortality ascertained within 60 days of an index positive SARS-CoV-2 test.

KEY RESULTS

Of 4,599 veterans with a positive SARS-CoV-2 test, vitamin D deficiency (< 20 ng/mL) was identified in 665 (14.5%); 964 (21.0%) were hospitalized; and 340 (7.4%) died. After adjusting for all covariates, including race/ethnicity and poverty, there was a significant independent inverse dose-response relationship between increasing continuous 25(OH)D concentrations (from 15 to 60 ng/mL) and decreasing probability of COVID-19-related hospitalization (from 24.1 to 18.7%, p=0.009) and mortality (from 10.4 to 5.7%, p=0.001). In modeling 25(OH)D as a log-transformed continuous variable, the greatest risk for hospitalization and death was observed at lower 25(OH)D concentrations.

CONCLUSIONS

Continuous blood 25(OH)D concentrations are independently associated with COVID-19-related hospitalization and mortality in an inverse dose-response relationship in this large racially and ethnically diverse cohort of VA patients. Randomized controlled trials are needed to evaluate the impact of vitamin D supplementation on COVID-19-related outcomes.

Physiological significance of vitamin D produced in skin compared with oral vitamin D

Since the discovery of vitamin D, it has been accepted that its physiological supply is either from food or by endogenous synthesis in skin exposed to solar UV light. Yet vitamin D is a component of very few foods and its supply as a natural nutrient is unable to maintain good vitamin D status for human populations. One aspect of vitamin D physiology that has been ignored is that the mechanisms for its transport and processing from these two sources are quite different. Excess intake of vitamin D causes hypercalcaemic toxicity. However, experiments with different animal species have shown that long-term supply of oral vitamin D in apparently non-toxic amounts causes atherosclerosis in large arteries. A mechanism for this toxicity is proposed. Alternative strategies for addressing widespread vitamin D deficiency by food fortification should be considered in light of the angiotoxicity caused by oral vitamin D in animal experiments.

Vitamin D in Alzheimer's Disease: Low Levels in Cerebrospinal Fluid Despite Normal Amounts in Serum

BACKGROUND

Vitamin D insufficiency has been suggested as a dementia risk factor.

OBJECTIVE

In this cross-sectional, explorative study we investigated whether levels of vitamin D in cerebrospinal fluid (CSF) are lower in patients with positive biomarkers of Alzheimer's disease (AD) compared to cognitively healthy controls and whether polymorphisms of the vitamin D receptor (VDR) gene, FokI, BsmI, ApaI, and TaqI, are associated with levels of vitamin D in CSF and cognition.

METHODS

We included 100 patients≥65 years assessed for cognitive impairment and 76 cognitively healthy controls. Levels of 25-hydroxyvitamin D (25(OH)D) in both serum and CSF, and VDR polymorphisms were analyzed.

RESULTS

The mean level of 25(OH)D in serum was 78.6 (SD 28.9) nmol/l. While serum levels of 25(OH)D were not significantly different between the groups, CSF levels of 25(OH)D were significantly lower in patients with positive AD core biomarkers (p = 0.001) compared to patients without such biomarkers. Individuals with the BsmI major homozygote genotype had significantly lower results on a 10-word delayed recall test (p = 0.044) and verbal fluency test (p = 0.013), and individuals with the TaqI major homozygote genotype had significantly lower results on a verbal fluency test (p = 0.030) compared to individuals with the corresponding minor homozygote genotype.

CONCLUSION

Patients with positive AD core biomarkers have low CSF levels of 25(OH)D, despite sufficient serum levels. CSF levels of 25(OH)D do not seem to be affected by any of the four VDR gene polymorphisms. TaqI and BsmI major homozygote genotypes might be at increased risk for development of cognitive decline.

Absence of Vitamin D Deficiency Among Outdoor Workers With Type 2 Diabetes Mellitus in Southern West Bengal, India

Background: Vitamin D deficiency is widespread globally and is associated with type 2 diabetes mellitus (T2DM). Studies suggest markedly lower prevalence of vitamin D deficiency in outdoor workers compared to indoor workers. However, data on the vitamin D status of outdoor workers with T2DM is lacking.

Aims: We assessed the vitamin D status of outdoor workers with T2DM residing across several districts of Southern West Bengal, India.

Design: The present study is a descriptive observational study.

Material and methods: A total of 128 outdoor workers with T2DM were assessed for serum 25-hydroxyvitamin D (25(OH)D) during December 2019 after excluding common confounders except sun exposure (which was detailed using a questionnaire). Hospital staff were indoor controls, and vitamin D status was classified as per the Institute of Medicine guidelines.

Results: The mean serum 25(OH)D of outdoor workers with T2DM was 21.79 ± 6.31 ng/mL, with only 2.34% (n = 3) having vitamin D deficiency and 57.03% (n = 73) having sufficient serum 25(OH)D levels. The mean serum 25(OH)D of indoor controls was significantly lower at 16.67 ± 9.82 ng/mL (p = 0.003), with 33.33% being vitamin D deficient. Serum 25(OH)D in outdoor workers with T2DM did not have a significant correlation with indices of sun exposure.

Conclusions: Vitamin D deficiency is practically absent in outdoor workers with T2DM residing in Southern West Bengal, India.

Total and free vitamin D status among apparently healthy adults living in Duhok Governorate

Serum total 25‐OHD is a main marker of vitamin D which represents the intake and sunlight exposure. Free form of 25‐OHD, the small fraction not bound to a transporter protein has been incorporated as a new marker. This cross-sectional study aimed to evaluate the impact of several factors on total and free vitamin D levels in healthy subjects and to find out if the free form of vitamin D could be a better representative of the body’s vitamin D status. Total and free 25‐OHD were analyzed by ELISA method in a blood sample collected from 391 apparently healthy volunteers (219 female and 172 Male) from Duhok Governorate/Iraq population. Total and free 25‐OHD levels were increased proportionally to BMI with lower values seen in the underweight group, also a significant gender differences in total D3 level with higher values in males (23.90 ± 16.41) ng/ml than females (21.24 ± 15.65) ng/ml was observed. Total and Free 25‐OHD levels were significantly associated with ages, their deficiency most frequent occurs in the younger ages between (16–25) years old. Smokers had higher level of Total 25‐OHD (26.95 ± 19.01) ng/ml and Free 25‐OHD (9.47 ± 4.94) pg/ml than nonsmokers (22.14 ± 14.59) ng/ml and (7.87 ± 4.32) pg/ml respectively. A significant increase in Free 25‐OHD level in the veiled women (9.12 ± 4.64) ng/ml than unveiled (6.16 ± 3.73) ng/ml with a significant positive correlation between Free 25‐OHD level and dress style was also seen. 30% and 33% of the participants whom their daily exposure to sunlight for 30 min and > 1 h respectively were severe deficient in total 25‐OHD. 95% of the participants who had Abnormally low level of free D were exposed for ≥ 30 min to sunlight. Daily exposure to sunlight was negatively associated with Free 25‐OHD level.

Total and free vitamin D metabolites in patients with primary hyperparathyroidism

PURPOSE

To evaluate total and free vitamin D metabolites and hormone-to-prohormone [1,25(OH)₂D/25(OH)D] "activation ratio" in PHPT patients with low or insufficient vitamin D status.

METHODS

Thirty female patients with primary hyperparathyroidism (PHPT) and 30 age and body mass index (BMI) matched healthy controls were enrolled. Serum levels of calcium, intact parathyroid hormone (iPTH), vitamin D binding protein (DBP), albumin, total 25(OH)D and 1,25(OH)₂D were measured. The activation ratio of vitamin D was calculated as total 1,25(OH)₂D/25(OH)D. Calculated serum-free 25(OH)D and 1,25(OH)₂D levels were also reported.

RESULTS

Compared to the control subject, patients with PHPT had a lower total 25(OH)D and DBP levels (p < 0.001). The serum concentration of free 25(OH)D and total 1,25(OH)₂D were similar between the two groups; but free 1,25(OH)₂D levels were about 26% higher in the PHPT patients compared to controls (p < 0.001). PHPT patients had a significantly higher activation ratio (p < 0.01), although their total 25(OH)D were lower than controls. The free (but not total) 1,25(OH)₂D level was inversely correlated with DBP (p < 0.01). Both free 1,25(OH)₂D levels and activation ratio were positively correlated with iPTH and calcium levels (p < 0.01). The activation ratio was highly correlated with levels of total vitamin D stores and free vitamin D metabolites (p < 0.001).

CONCLUSION

Patients with PHPT had significantly higher free 1,25(OH)₂D levels and activation ratio compared to control subjects. We suggest that levels of free vitamin D metabolites and vitamin D activation ratio may provide additional values for the diagnosis and therapeutic choices in these patient populations with compromised vitamin D status.

An Update on Vitamin D Deficiency in the twenty-first century: nature and nurture

PURPOSE OF REVIEW

Here, we review the most up-to-date understanding of the pathogenesis, prevention and treatment of vitamin D deficient rickets in children. This will include recent advances in the genetic determinants of abnormal vitamin D metabolism, with the intention of aiding clinicians with establishing the diagnosis and implementing treatment plans for children presenting with vitamin D deficiency rickets.

RECENT FINDINGS

Vitamin D deficiency rickets is a frequently encountered, but entirely preventable, disorder of bone mineral metabolism. Risk factors for developing vitamin D deficiency rickets include inadequate exposure to sunlight, exclusive breast feeding without vitamin D supplementation and inadequate intake of vitamin D, calcium or phosphorus. Other factors that may influence the development of vitamin D deficiency and/or rickets include genetic alterations or medications that alter vitamin D metabolism.

SUMMARY

Vitamin D levels in individuals are influenced by environmental factors, as well as genetic factors. A thorough understanding of these factors is critical for the evaluation and treatment of a child presenting with rickets. There remains a great need for additional research to determine ideal vitamin D status across diverse populations, and to better understand how vitamin D status affects overall health.

Influences of vitamin D levels and vitamin D binding protein polymorphisms on non-alcoholic fatty liver disease risk in a Chinese population

INTRODUCTION

Vitamin D binding protein (VDBP) is correlated with non-alcoholic fatty liver disease (NAFLD) through the biological functions of regulating plasma vitamin D (VD) level and the inflammatory process.

OBJECTIVE

This study aims to investigate the effects of VD level and VDBP gene polymorphisms on the risk of NAFLD in a Chinese population.

METHODS

Plasma 25-hydroxyvitamin D3 [25(OH)D3] levels were measured and seven VDBP candidate genetic variants (rs222020, rs2282679, rs4588, rs1155563, rs7041, rs16847024, rs3733359) were genotyped among participants in this case-control study. The control group was frequency-matched to NAFLD case group by age and gender. Correlation analysis and multiple linear regression were used to screen determinants of 25(OH)D3 levels. Multivariable unconditional logistic regression was performed to estimate odds ratio (OR) and 95% confidence interval (95% CI). The prediction capability of models containing independent factors was estimated by the area under the receiver operating characteristic curve (AUROC) and Hosmer-Lemeshow test.

RESULTS

Age, BMI and TG were independent factors influencing VD levels. Participants with low VD levels had significantly higher prevalence of NAFLD compared to subjects with normal VD levels (P < 0.001). A low VD level contributed to increased risk of NAFLD, independent of metabolic factors known to affect VD levels (adjusted OR = 2.282, 95% CI = 1.422-3.661, P = 0.001). Logistic regression analysis showed that individuals carrying rs7041-G allele had a significantly decreased risk of NAFLD occurrence compared to T allele (additive model: adjusted OR = 0.814, 95% CI = 0.713-0.929, P = 0.002; codominant model: adjusted OR = 0.623, 95% CI = 0.449-0.866, P = 0.005), after adjusting for age, gender, and overweight. Stratification by multiple metabolic disorders did not alter this relationship. Moreover, we developed a simple model including age, gender, metabolic disorders and VDBP SNP to assess NAFLD risk, an AUC of which being 0.817, significantly higher than the model not included VDBP SNP, with Hosmer-Lemeshow test fitting well (P = 0.182).

CONCLUSIONS

Low plasma VD levels may increase susceptibility to NAFLD, while rs7041-G allele in VDBP contributed to a decreased NAFLD risk among Chinese population. The VDBP variant significantly improved the capability for NAFLD risk assessment, which could be used for early screening and management of NAFLD.