Unbound Vitamin D Concentrations Are Not Decreased in Critically Ill Patients

Measurement of Serum Free Vitamin D Concentrations: Importance, Challenges, and the Emerging Role of Mass Spectrometry

BACKGROUND

Serum total 25-hydroxyvitamin D [25(OH)D] concentration is the most widely used clinical biomarker for vitamin D status. Under certain physiological and pathological conditions, however, total 25(OH)D may not always be the best index for vitamin D status. Instead, the nonprotein-bound (free) fraction of total 25(OH)D has been suggested as a more appropriate marker in certain clinical situations.

CONTENT

Free 25(OH)D levels can either be calculated or measured directly. Calculated free 25(OH)D depends on the concentrations of total serum 25(OH)D, vitamin D binding protein (VDBP), and albumin, as well as the affinity between analyte and binding proteins. Differences in VDBP concentrations are observed between populations as a result of health status, gene polymorphisms, and the assay used for determination. Direct measurement methods for free 25(OH)D are often complicated (dialysis, ultrafiltration) or susceptible to interferences, cross-reactivity, and type of antibody (immunoassays). Therefore, it is very important to develop tools that allow either accurate and precise measurement of VDBP or direct measurement of free 25(OH)D. For the latter, liquid chromatography combined with tandem mass spectrometry (LC-MS/MS) has recently shown promise for analysis of free vitamin D. In the current review, we present the importance and challenges regarding free 25(OH)D determination and the role of LC-MS-based methods in future studies.

SUMMARY

More research is required to determine the role of free 25(OH)D in the assessment of vitamin D status in healthy subjects and in various clinical conditions. Recent advances in technology, including mass spectrometry, can provide the required assays for this purpose.

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.

Notable Developments for Vitamin D Amid the COVID-19 Pandemic, but Caution Warranted Overall: A Narrative Review

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a novel contagion that has infected over 113 million people worldwide. It is responsible for the coronavirus disease (COVID-19), which has cost the lives of 2.5 million people. Ergo, the global scientific community has been scrambling to repurpose or develop therapeutics to treat COVID-19. Dietary supplements and nutraceuticals are among those under consideration due to the link between nutritional status and patient outcomes. Overall, poor vitamin D status seems to be associated with an increased risk of COVID-19. Severely ill COVID-19 patients appear to be deficient or have suboptimal levels of serum 25-hydroxyvitamin D, a measure of vitamin D status. Consequently, vitamin D is now the subject of several prophylactic and therapeutic clinical trials. In this review, the general status of nutraceuticals and dietary supplements amid the pandemic is appraised, with a particular focus on vitamin D. Consumers should be aware of misinformation and unsubstantiated promises for products marketed for COVID-19 protection. However, maintaining a healthy diet and lifestyle will likely maintain health including optimum immune function that may affect patient outcomes. Those who are deficient in key nutrients such as vitamin D should consider lifestyle changes and potentially supplementation in consultation with their physician and/or registered dieticians.

Prevalence and Impact of Vitamin D Deficiency in Critically Ill Cancer Patients Admitted to the Intensive Care Unit

Vitamin D deficiency is frequent in cancer patients and a risk factor for morbidity and mortality during critical illness. This single-center retrospective study analyzed 25-hydroxyvitamin D levels in critically ill cancer patients (n = 178; hematologic, n = 108; solid, n = 70) enrolled in a prospective ICU registry. The primary analysis was the prevalence of vitamin D deficiency (<20 ng/mL) and the severe deficiency (≤12 ng/mL). Secondary analyses included risk factors for vitamin D deficiency and its impact on ICU, hospital, and 1-year mortality. The prevalence of vitamin D deficiency and severe deficiency was 74% (95% CI: 67-80%) and 54% (95% CI: 47-61%). Younger age, relapsed/refractory disease, and a higher sepsis-related organ failure assessment (SOFA) score were independent risk factors for vitamin D deficiency (p < 0.05). After adjusting for relapsed/refractory disease, infection, the SOFA score, and the early need for life-supporting interventions, severe vitamin D deficiency was an independent predictor of hospital mortality (OR: 2.21, 95% CI: 1.03-4.72, p = 0.04) and 1-year mortality (OR: 3.40, 95% CI: 1.50-7.71, p < 0.01), but not of ICU mortality. Conclusion: Vitamin D deficiency is common in critically ill cancer patients requiring ICU admission, but its impact on short-term mortality in this group is uncertain. The observed association of severe vitamin D deficiency with the post-ICU outcome warrants clinical consideration and further study.