Optimal vitamin D supplementation strategies

Role of vitamin D in prevention of type 2 diabetes mellitus: A systematic review and meta‑analysis

The escalating prevalence of diabetes mellitus, projected to affect over 700 million by 2045, underscores the urgent need for effective management and prevention strategies, with type 2 diabetes mellitus (T2DM) constituting over 90% of these cases globally. The present meta-analysis aims to rigorously evaluate the potential of vitamin D supplementation in mitigating the onset of T2DM, amidst the backdrop of its biological plausibility yet inconclusive evidence regarding its efficacy in reducing new incidences of the disease. A comprehensive literature search up to December 2023 in MEDLINE, EMBASE and the Cochrane Library, employing a strategy focused on diabetes and vitamin D, identified randomized controlled trials (RCTs) that explore the impact of vitamin D supplementation on T2DM onset in adults with impaired glucose regulation, incorporating quality assessment via the Cochrane ROB2 tool and utilizing meta-analysis with RevMan Web to evaluate effect magnitude and heterogeneity. In a meta-analysis of 11 RCTs with 5,221 prediabetic patients, vitamin D supplementation was associated with a 10% reduction in the progression to T2DM [RR, 0.90; 95% CI, (0.81-0.99)] and a significant increase in regression to normoglycemia [RR, 1.24; 95% CI, (1.08-1.43)], with no significant heterogeneity or publication bias observed. This meta-analysis of 11 RCTs shows that vitamin D supplementation in prediabetic patients lowers the risk of T2DM and promotes regression to normoglycemia, with no significant differences in subgroup analyses or interaction with baseline vitamin D levels, ethnicity, or body mass index (BMI). Despite indications from some trials that baseline vitamin D status may influence outcomes, the present comprehensive analysis found benefits of vitamin D across diverse populations, including non-obese individuals, without conclusive evidence linking supplementation to changes in BMI or age-specific advantages.

Vitamin D supplementation and immune-related markers: an update from nutrigenetic and nutrigenomic studies

Vitamin D is both a nutrient and a neurologic hormone that plays a critical role in modulating immune responses. While low levels of vitamin D are associated with increased susceptibility to infections and immune-related disorders, vitamin D supplementation has demonstrated immunomodulatory effects that can be protective against various diseases and infections. Vitamin D receptor is expressed in immune cells that have the ability to synthesise the active vitamin D metabolite. Thus, vitamin D acts in an autocrine manner in a local immunologic milieu in fighting against infections. Nutrigenetics and nutrigenomics are the new disciplines of nutritional science that explore the interaction between nutrients and genes using distinct approaches to decipher the mechanisms by which nutrients can influence disease development. Though molecular and observational studies have proved the immunomodulatory effects of vitamin D, only very few studies have documented the molecular insights of vitamin D supplementation. Until recently, researchers have investigated only a few selected genes involved in the vitamin D metabolic pathway that may influence the response to vitamin D supplementation and possibly disease risk. This review summarises the impact of vitamin D supplementation on immune markers from nutrigenetics and nutrigenomics perspective based on evidence collected through a structured search using PubMed, EMBASE, Science Direct and Web of Science. The research gaps and shortcomings from the existing data and future research direction of vitamin D supplementation on various immune-related disorders are discussed.

Vitamin D status and vitamin D deficiency risk factors among pregnancy of Shanghai in China

Background

There is increasing awareness that vitamin D deficiency in pregnant women may be associated with several adverse effects for the mother and newborn. The risks for vitamin D deficiency are unclear. This study was to assess vitamin D nutritional status and vitamin D deficiency risk factors among pregnant women in Shanghai in China.

Methods

This study is a cross-sectional study conducted in the Sixth Affiliated People’s Hospital of Shanghai Jiao Tong University. A total of 953 healthy pregnant women participated, serological examinations and other variables included serum 25-hydroxyvitamin D [25(OH)D], total blood cholesterol (TCh), high-density lipoprotein (HDL), low-density lipoprotein (LDL), and very-low-density lipoprotein (VLDL) cholesterol, triglycerides at the first antenatal visit (12–14 weeks) pregnancy parity and age, body mass index (BMI) before pregnancy, and completed OGTTs test. Associations between vitamin D deficiency and possible predictors (age group, pre-pregnancy BMI, parity, and gestational hyperlipemia) were assessed with a multinomial logistic regression analysis. And also used to investigate the effects of 25(OH)D and the other variables on the occurrence of gestational diabetes mellitus.

Results

The mean vitamin D level of pregnancy was 16 (a range from 11 to 21) ng/ml, and severe vitamin D deficiency was 31.8% (303); vitamin D deficiency was 40.7% (388); vitamin D insufficiency was 25.1% (239); normal vitamin D was 2.4%(23). Vitamin D deficiency risk factors were age over 30, parity over 2, overweight, obese, and hyperlipemia. The increasing level of vitamin D nutritional status in pregnancy is significantly related to reducing gestational diabetes mellitus. Vitamin D deficiency is a risk factor for gestational diabetes mellitus.

Conclusions

It is a high prevalence of vitamin D deficiency in Chinese pregnancy in Shanghai. Aging more than 30 years, the parity of more than 2, overweight and obesity, and hyperlipemia are risk factors for vitamin D deficiency. Vitamin D deficiency is a risk factor for gestational diabetes mellitus. Public health strategies to prevent vitamin D deficiency should focus on those risks to promote health pregnancy of Shanghai in China.

Effects of select dietary supplements on the prevention and treatment of viral respiratory tract infections: a systematic review of randomized controlled trials

Introduction: Viral respiratory tract infections (RTIs) have been recognized as a global public health burden. Despite current theories about their effectiveness, the true benefits of dietary supplements on the prevention and treatment of viral RTIs remain elusive, due to contradictory reports. Hence, we aimed to evaluate the effectiveness of dietary supplements on the prevention and treatment of viral RTIs.Areas covered: We systematically searched databases of PubMed, Web of Science, Scopus, and Google Scholar through 4 March 2020, to identify randomized controlled trials that evaluated the effects of consuming selected dietary supplements on the prevention or treatment of viral RTIs.Expert opinion: Thirty-nine randomized controlled trials (n = 16,797 participants) were eligible and included. Namely, vitamin D supplementation appeared to improve viral RTIs across cohorts particulate in those with vitamin D deficiency. Among the evaluated dietary supplements, specific lactobacillus strains were used most commonly with selected prebiotics that showed potentially positive effects on the prevention and treatment of viral RTIs. Further, ginseng extract supplementation may effectively prevent viral RTIs as adjuvant therapy. However, longitudinal research is required to confirm these observations and address the optimal dose, duration, and safety of dietary supplements being publicly recommended.

Effectiveness and safety of steady versus intermittent high dose vitamin D supplementation for the prevention of falls and fractures among adults: a protocol for systematic review and network meta-analysis

INTRODUCTION

Clinical trials and systematic reviews of trials involving vitamin D supplementation have mainly focused on defining the optimal amount of vitamin D dosage. However, the comparative effectiveness of different dosing schedules (ie, daily vs bolus dosing schedule) has been largely unexplored; and currently, there is no consensus regarding the optimal vitamin D dosing schedule. Our objective is to conduct a systematic review and network meta-analysis (NMA) to evaluate the comparative effectiveness and safety of steady (eg, daily, weekly) and intermittent high-dose (eg, monthly, yearly) vitamin D dosing schedules; and to determine the effectiveness of the various dosing schedules and combinations of treatments.

METHODS AND ANALYSIS

We will conduct a systematic search and review of literature from major medical databases (MEDLINE, EMBASE, CINAHL, Cochrane Central Register of Controlled Trials and ClinicalTrials.gov) involving studies that compare vitamin D supplementation alone or in combination with calcium. Only randomised controlled trials (RCTs) will be considered. We will, however, consider various settings (eg, community, institutional care) and study designs (eg, cluster RCTs, cross-over trials). Our primary outcomes include falls and fractures including hip-fracture and non-vertebral fractures. Secondary outcomes will include muscle strength, physical performance, gait and mobility limitation. A Bayesian NMA will be conducted, and the results will be presented in the form of treatment effect estimates and ranking probabilities, with corresponding CIs. Pairwise meta-analysis will also be conducted for studies reporting head-to-head comparisons. Subgroup analysis will be performed with respect to pre-determined subgroups; including vitamin D status as measured by serum 25-hydroxyvitamin D levels, age and follow-up time. Sensitivity analysis will also be performed with respect to risk of bias.

ETHICS AND DISSEMINATION

This study is a systematic review and meta-analysis of published RCTs; therefore, no ethical approval is required. Results will be disseminated through open access peer-reviewed publications.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO CRD42018112662.

Why vitamin D clinical trials should be based on 25-hydroxyvitamin D concentrations

Many health benefits are attributed to vitamin D, with those findings supported mostly by observational outcome studies of relationships to serum 25-hydroxyvitamin D [25(OH)D]. However, many randomized controlled trials (RCTs) aiming to confirm those findings have failed, perhaps because serum 25(OH)D is an index of UVB exposure and non-vitamin D mechanisms or because disease reduces serum 25(OH)D content. But the most likely reason for that failure is inappropriate design, conduct, analysis, and interpretation of RCTs. Most RCTs used principles designed to test pharmaceutical drugs; that design incorporates the assumptions that the RCT is the sole source of the agent and that dose-response relationships are linear. However, neither assumption is true for vitamin D, since neither vitamin D dose-responses or health outcome-serum 25(OH)D concentration relationships are linear-larger changes being induced with low rather than high baseline 25(OH)D values. Here, we propose a hybrid observational approach to vitamin D RCT design, based primarily on serum 25(OH)D concentration, requiring an understanding of serum 25(OH)D concentration-health outcome relationships, measuring baseline 25(OH)D values, recruiting non-replete subjects, measuring serum 25(OH)D during the trial for adjustment of supplemental doses for achievement of pretrial selection of target 25(OH)D values, where possible, and analyzing health outcomes in relation to those data rather than solely to vitamin D dosages.

A kidney-specific genetic control module in mice governs endocrine regulation of the cytochrome P450 gene Cyp27b1 essential for vitamin D3 activation

The vitamin D endocrine system regulates mineral homeostasis through its activities in the intestine, kidney, and bone. Terminal activation of vitamin D₃ to its hormonal form, 1α,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃), occurs in the kidney via the cytochrome P450 enzyme CYP27B1. Despite its importance in vitamin D metabolism, the molecular mechanisms underlying the regulation of the gene for this enzyme, Cyp27b1, are unknown. Here, we identified a kidney-specific control module governed by a renal cell-specific chromatin structure located distal to Cyp27b1 that mediates unique basal and parathyroid hormone (PTH)-, fibroblast growth factor 23 (FGF23)-, and 1,25(OH)₂D₃-mediated regulation of Cyp27b1 expression. Selective genomic deletion of key components within this module in mice resulted in loss of either PTH induction or FGF23 and 1,25(OH)₂D₃ suppression of Cyp27b1 gene expression; the former loss caused a debilitating skeletal phenotype, whereas the latter conferred a quasi-normal bone mineral phenotype through compensatory homeostatic mechanisms involving Cyp24a1 We found that Cyp27b1 is also expressed at low levels in non-renal cells, in which transcription was modulated exclusively by inflammatory factors via a process that was unaffected by deletion of the kidney-specific module. These results reveal that differential regulation of Cyp27b1 expression represents a mechanism whereby 1,25(OH)₂D₃ can fulfill separate functional roles, first in the kidney to control mineral homeostasis and second in extra-renal cells to regulate target genes linked to specific biological responses. Furthermore, we conclude that these mouse models open new avenues for the study of vitamin D metabolism and its involvement in therapeutic strategies for human health and disease.