Non-genomic action of vitamin D3 on N-methyl-D-aspartate and kainate receptor-mediated actions in juvenile gonadotrophin-releasing hormone neurons

Association of vitamin D and cognition in people with type 2 diabetes: a systematic review

CONTEXT

There is a high prevalence of vitamin D deficiency and impaired cognitive function in people with type 2 diabetes mellitus (T2DM).

OBJECTIVE

To critically and systematically review the literature on the association between vitamin D status and cognitive performance in people with type 2 diabetes.

DATA SOURCES

This review was conducted according to PRISMA recommendations. MEDLINE, SCOPUS, the Cochrane Library, and Web of Science databases were searched using the terms "Diabetes Mellitus, Type 2", "Cognitive Function", and "Vitamin D".

DATA EXTRACTION

Eight observational and 1 randomized study were included, containing data of 14 648 adult and elderly individuals (19-74 y). All extracted data were compiled, compared, and critically analyzed.

DATA ANALYSIS

There is no strong evidence that lower serum concentrations of vitamin D and vitamin D-binding protein are associated with worsening cognitive function in individuals with T2DM. Vitamin D supplementation (12 wk) improved the scores of some executive functioning tests, although there was no difference between low doses (5000 IU/wk) and high doses (50 000 IU/wk).

CONCLUSIONS

There is no high-quality evidence demonstrating an association between vitamin D status and cognitive function, or clinical benefits on cognition from vitamin D supplementation in individuals with T2DM. Future studies are needed. Systematic Review Registration: PROSPERO registration no. CRD42021261520.

Effects of vitamin D on sex steroids, luteinizing hormone, and testosterone to luteinizing hormone ratio in 307 infertile men

OBJECTIVE

Vitamin D status has been associated with sex steroid production. The question is whether vitamin D supplementation has an impact on sex steroid production in infertile men with vitamin D insufficiency?

DESIGN

A single-center, double-blinded, randomized clinical trial. Differences in sex steroids and reproductive hormones were predefined secondary outcomes, vitamin D status at baseline was a predefined subgroup and the primary outcome was differences in semen quality.

METHODS

A total of 307 infertile men were included and randomized 1:1 to active or placebo treatment for 150 days. Men in the active group initially received an oral bolus of 300,000 IU cholecalciferol, followed by daily supplementation with 1400 IU cholecalciferol and 500 mg calcium.

RESULTS

After intervention, no differences were found in serum concentrations of sex steroids, luteinizing hormone, testosterone/luteinizing hormone ratio or SHBG between the vitamin D and placebo group. However, in a predefined subgroup analysis of men with serum 25OHD ≤ 50 nmol/L, men treated with vitamin D had a significantly higher testosterone/luteinizing hormone ratio [4.2 (3.8-4.4) vs. 3.7 (3.4-4.0); p = 0.033] compared with placebo treatment. In men with vitamin D deficiency, the difference between groups was larger but not significant due to few men with serum 25OHD < 25 nmol/L.

CONCLUSION

Vitamin D + calcium supplementation did not alter sex steroid production in infertile men. However, vitamin D insufficient men treated with vitamin D supplementation had a significantly higher testosterone/LH ratio compared with placebo-treated men, suggesting that optimal Leydig cell function are dependent on adequate vitamin D status.

Molecular Regulation of the CNS by Vitamin D

Vitamin D is a lipid-soluble vitamin that can be found in some foods. It is also produced endogenously (in the presence of ultraviolet light), transported through the blood to the targets organs and this is the reason to consider vitamin D as a hormone. It is known that vitamin D has genomic and non-genomic effects. This review is focused mainly on the vitamin D receptors, the importance of vitamin D as a neuromodulator, the role of vitamin D in the pathophysiology of devastating neurological disorders such as Alzheimer's disease, multiple sclerosis, amyotrophic lateral sclerosis, Parkinson's disease and the benefit of vitamin D and its derivates in alleviating these disorders.

An update of the effects of vitamins D and C in critical illness

Many critically ill patients are vitamin D and vitamin C deficient and the current international guidelines state that hypovitaminoses should be compensated. However, uncertainty about optimal dosage, timing and indication exists in clinical routine, mainly due to the conflicting evidence. This narrative review discusses both micronutrients with regards to pathophysiology, clinical evidence of benefits, potential risks, and guideline recommendations. Evidence generated from the most recent clinical trials are summarized and discussed. In addition, pragmatic tips for the application of these vitamins in the clinical routine are given. The supplementations of vitamin D and C represent cost-effective and simple interventions with excellent safety profiles. Regarding vitamin D, critically ill individuals require a loading dose to improve 25(OH)D levels within a few days, followed by a daily or weekly maintenance dose, usually higher doses than healthy individuals are needed. For vitamin C, dosages of 100-200 mg/d are recommended for patients receiving parenteral nutrition, but needs may be as high as 2-3 g/d in acutely ill patients.

In vivo electrophysiological study of vitamin D3 protective effects on PTZ-induced seizures in rats

Background and purpose

The purpose of the current study was to investigate the protective effects of acute and chronic administration of different doses of vitamin D3 on pentylenetetrazol (PTZ)-induced epileptiform activities in rats.

Experimental approach

Sixty Wistar rats in chronic and acute groups were used in this study. In the chronic groups, animals received vitamin D3 at 50, 100, and 150 μg/kg; vitamin D3 (50 μg/kg, i.p.) + diazepam (0.1 mg/kg, i.p.), and almond oil (i.p.) daily for two weeks whereas, in the acute groups the animal received a single dose of chemicals just 30 min before PTZ administration. The electrophysiological recording was performed by implanting a unilateral bipolar electrode in the pyramidal cell layer of the CA1 region of the hippocampus. Epileptic activities were induced by intraperitoneal injection of PTZ (80 mg/kg, i.p.). The spike count and amplitude were analyzed using the eTrace software.

Finding/Results

Chronic administration of all doses of vitamin D3 and its combination with diazepam significantly reduced both spike counts and amplitudes following PTZ administration. While the acute doses were ineffective.

Conclusion and implication

The results of the study indicated that chronic but not acute administration of vitamin D3 has a protective effect on PTZ-induced epileptiform activity in rats.

Vitamin D and calcium, together and separately, play roles in female reproductive performance

Vitamin D (VD) deficiency reduces the chances of successful fertilization; however, it remains to be validated whether this effect is dependent or not on calcium. To address this question, we generated several situation using a mouse model in which VD content was either increased or decreased in a normo or hypocalcemia context. After the measurement of serum 25-hydroxyvitamin D₂, calcium and phosphorus levels, an analysis was carried out in terms of oocytes maturation as well as reproductive performance. VD overdose, despite the fact that it resulted in an increased number of mature oocytes, reduced developmental competence and offspring survival. VD deficiency (VDD), on the contrary, reduced the number and percentage of mature oocytes, blastocyst rate, as well as fertility rate and offspring survival. Hypo-calcemia when VD levels were normal, had a similar effect than VDD. The effects of VDD were reversed by a diet that corrected calcium level. Therefore, both VD overdose (in a context of normal calcium level) VD deficiency as well as hypo-calcemia have an effect on female reproductive function. In conclusion, although closely related, VD and calcium act in part independently of each other in defining the “optimum” for female reproductive performance.

Vitamin D: A Potential Star for Treating Chronic Pancreatitis

Chronic pancreatitis (CP) is a chronic inflammatory and fibrotic disease of the pancreas. The incidence of CP is increasing worldwide but the effective therapies are lacking. Hence, it is necessary to identify economical and effective agents for the treatment of CP patients. Vitamin D (VD) and its analogues have been confirmed as pleiotropic regulators of cell proliferation, apoptosis, differentiation and autophagy. Clinical studies show that VD deficiency is prevalent in CP patients. However, the correlation between VD level and the risk of CP remains controversial. VD and its analogues have been demonstrated to inhibit pancreatic fibrosis by suppressing the activation of pancreatic stellate cells and the production of extracellular matrix. Limited clinical trials have shown that the supplement of VD can improve VD deficiency in patients with CP, suggesting a potential therapeutic value of VD in CP. However, the mechanisms by which VD and its analogues inhibit pancreatic fibrosis have not been fully elucidated. We are reviewing the current literature concerning the risk factors for developing CP, prevalence of VD deficiency in CP, mechanisms of VD action in PSC-mediated fibrogenesis during the development of CP and potential therapeutic applications of VD and its analogues in the treatment of CP.

TRPV1 channels as a newly identified target for vitamin D

Vitamin D is known to elicit many biological effects in diverse tissue types and is thought to act almost exclusively upon its canonical receptor within the nucleus, leading to gene transcriptional changes and the subsequent cellular response. However, not all the observed effects of vitamin D can be attributed to this sole mechanism, and other cellular targets likely exist but remain to be identified. Our recent discovery that vitamin D is a partial agonist of the Transient Receptor Potential Vanilloid family 1 (TRPV1) channel may provide new insights as to how this important vitamin exerts its biological effects either independently or in addition to the nuclear vitamin D receptor. In this review, we discuss the literature surrounding this apparent discrepancy in vitamin D signaling and compare vitamin D with known TRPV1 ligands with respect to their binding to TRPV1. Furthermore, we provide evidence supporting the notion that this novel vitamin D/TRPV1 axis may explain some of the beneficial actions of this vitamin in disease states where TRPV1 expression and vitamin D deficiency are known to overlap. Finally, we discuss whether vitamin D may also act on other members of the TRP family of ion channels.

[Vitamin D and reproductive health]

Vitamin D insufficiency and deficiency in women with infertility is more common than in the population. However, we still do not know the exact mechanisms for the participation of vitamin D in the regulation of reproductive function. The purpose of this study is to analyze actual literature data on the role of vitamin D in the regulation of reproductive system and its influence on using of assisted reproductive technologies for the treatment of infertility. A search was carried out for literary sources published in the NSBI database PubMed, Medline, and others with a search depth of up to 20 years. 135 sources on this topic were studied, of which 54 were included in the analysis. The review presents data obtained in animal studies, in vitro and in clinical studies. Thus, the absence of vitamin D resulted in a dramatical decrease in fertility in both female and male rats and mice, due to the development of hypocalcemia. In vitro studies describe its involvement in the receptive transformation of the endometrium and in the regulation of the immune response during embryo implantation. However, clinical studies often show conflicting results. There is no unequivocal data on the effect of vitamin D levels on spermogram parameters, but a decrease in the pregnancy rate was shown when ovulation was induced in pairs, where a vitamin D deficiency was revealed in men. A meta-analysis published in 2017 showed a decrease in the pregnancy and live birth rate in women with low levels of vitamin D after the use of assisted reproductive technologies (ART). It was not possible to establish whether this decrease depends on oocyte quality or endometrium. There is an opportunity that the effect of vitamin D deficiency on fertility will not come with all forms of infertility. For example, in women with anovulation due to polycystic ovary syndrome, vitamin D deficiency is demonstrated to decrease pregnancy rate in ovulation induction cycles and in ART. Such relationship was not found in women with unexplained infertility.Thus, the role of vitamin D in the pathogenesis of infertility requires further study, as well as the possibilities of therapy in order to increase the effectiveness of infertility treatment methods and assisted reproductive technology programs.

Health Risks of Hypovitaminosis D: A Review of New Molecular Insights

Hypovitaminosis D has become a pandemic, being observed in all ethnicities and age groups worldwide. Environmental factors, such as increased air pollution and reduced ultraviolet B (UVB) irradiation, as well as lifestyle factors, i.e., decreased outdoor activities and/or poor intake of vitamin D-rich food, are likely involved in the etiology of a dramatic reduction of vitamin D circulating levels. The insufficiency/deficiency of vitamin D has long been known for its association with osteoporosis and rickets. However, in the last few decades it has become a serious public health concern since it has been shown to be independently associated with various chronic pathological conditions such as cancer, coronary heart disease, neurological diseases, type II diabetes, autoimmune diseases, depression, with various inflammatory disorders, and with increased risk for all-cause mortality in the general population. Prevention strategies for these disorders have recently involved supplementation with either vitamin D2 or vitamin D3 or their analogs at required daily doses and tolerable upper-limit levels. This review will focus on the emerging evidence about non-classical biological functions of vitamin D in various disorders.