Effects of Vitamin D Supplementation on C-peptide and 25-hydroxyvitamin D Concentrations at 3 and 6 Months

A brief review of vitamin D as a potential target for the regulation of blood glucose and inflammation in diabetes-associated periodontitis

Diabetes is a metabolic disorder associated with various complications, including periodontitis. The risk of periodontitis is increased in patients with diabetes, while vitamin D deficiency is associated with both diabetes and periodontitis. Thus, there is a need to identify the molecular effects of vitamin D on the regulation of inflammation and glucose in diabetes-associated periodontitis. The Web of Science, Scopus, and PubMed databases were searched for studies of the molecular effects of vitamin D. Molecular effects were reportedly mediated by salivary secretions, interactions of advanced glycation end products (AGEs) with receptors of AGEs (RAGEs), cytokines, and oxidative stress pathways linking diabetes with periodontitis. Vitamin D supplementation attenuates inflammation in diabetes-associated periodontitis by reducing the levels of inflammatory cytokines and numbers of immune cells; it also has antibacterial effects. Vitamin D reduces cytokine levels through regulation of the extracellular signal-related kinase 1/2 and Toll-like receptor 1/2 pathways, along with the suppression of interleukin expression. Glucose homeostasis is altered in diabetes either because of reduced insulin production or decreased insulin sensitivity. These vitamin D-related alterations of glucoregulatory factors may contribute to hyperglycaemia; hyperglycaemia may also lead to alterations of glucoregulatory factors. This review discusses the pathways involved in glucose regulation and effects of vitamin D supplementation on glucose regulation. Further studies are needed to characterise the effects of vitamin D on diabetes-associated periodontitis.

The impact of preoperative vitamin administration on skeletal status following sleeve gastrectomy in young and middle-aged women: a randomized controlled trial

BACKGROUND

The appropriate strategies to minimize skeletal deterioration following bariatric surgeries are inconclusive. This randomized controlled trial evaluated the effect of preoperative vitamin supplementation on bone mineral density (BMD) and biochemical parameters in females post-sleeve gastrectomy (SG).

METHODS

Participants were randomized to a 2-month preoperative treatment with a multivitamin and vitamin D 4000 IU/d (intervention arm) or 1200 IU/d (control arm). Preoperative and 12-month postoperative follow-up evaluations included anthropometrics, biochemical parameters, and dual energy X-ray absorptiometry (DEXA).

RESULTS

Sixty-two females (median age 29.7 years and median BMI 43.4 kg/m²) were recruited, 87% completed the 12-month follow-up. For the intervention and control arms, significant and similar reductions at 12-months post-surgery were observed in BMD of the hip (-6.8 ± 3.7% vs. -6.0 ± 3.6%; P = 0.646) and of the femoral neck (-7.1 ± 5.8% vs. -7.2 ± 5.5%; P = 0.973). For the intervention compared to the control arm, the 25 hydroxyvitamin D (25(OH)D) increment was greater after 2 months treatment, and vitamin D deficiency rates were lower at 3 and 6-months follow-up (P < 0.016). However, at 12-months postoperative, 25(OH)D values and vitamin D deficiency were comparable between the arms (P > 0.339). Predictors for BMD decline in the total hip were the percentage of excess weight-loss, age>50 years, and lower initial BMI (P ≤ 0.003).

CONCLUSIONS

SG was associated with a significant decline in BMD of the hip and femoral neck in young and middle-aged women, and was unaffected by preoperative vitamin D supplementation. Females who are peri-menopausal or with greater postoperative weight-loss should be particularly followed for BMD decline.

A systematic review and meta-analysis of the response of serum 25-hydroxyvitamin D concentration to vitamin D supplementation from RCTs from around the globe

BACKGROUND/OBJECTIVES

Optimal doses of vitamin D (VitD) supplement in different populations are unclear. We aim to evaluate the relationship between VitD supplementation and post-intervention serum 25-hydroxyvitamin D [25(OH)D] concentration, to provide a recommended dosage of VitD for achieving an optimal 25(OH)D concentration for different populations.

SUBJECTS/METHODS

Literature search was conducted in Embase, etc. Randomized controlled trials about VitD supplemental intakes and their effect on 25(OH)D concentration were enrolled. The effect on 25(OH)D concentration between different supplementation doses in each population group was compared by meta-analysis. Multivariate meta-regression model is utilized to establish reference intake dosage of VitD.

RESULTS

A total of 136 articles were included about children (3-17 years), adults (18-64 years), postmenopausal women, the elderly ( >64 years), pregnant, or lactating women. Overall, intervention groups obtained higher 25(OH)D concentration than controls and there was obvious dose-response effect between intake dose and 25(OH)D concentration. Baseline 25(OH)D concentration and age were significant indicators for 25(OH)D concentration. To reach sufficient 25(OH)D concentration (75 nmol/L), the recommended VitD supplemental intakes was 1340 and 2250 IU/day for children and pregnant women, 2519 and 797 IU/day for European adults aged 18-64 and 65-85 years, 729, 2026, and 1229 IU/day for adults in North America, Asia and Middle East and Africa, respectively.

CONCLUSIONS

Regional- and age-specific recommended dosages of VitD supplements for population to achieve optimal 25(OH)D concentrations have been suggested.

Vitamin D supplementation in obesity and during weight loss: A review of randomized controlled trials

Vitamin D deficiency is common in obese individuals and during weight loss. The recommended vitamin D doses in this specific population are higher than for healthy adults. We reviewed vitamin D supplementation trials in obesity, and during medical or surgical weight loss, and report the effects on 25-hydroxyvitamin D [25(OH)D] concentrations and other relevant outcomes. We conducted a systematic search in PubMed, Medline, Embase and the Cochrane library for relevant randomized controlled trials (RCTs) of oral vitamin D supplementation for at least 3 months in obese individuals without weight loss (OB), and those on medical weight loss (MWL) (2010-2018), and following bariatric surgery (Bar S) (without time restriction). Two reviewers screened the identified citations in duplicate and independently and performed full text screening. One reviewer completed data extraction. We identified 13 RCTs in OB, 6 in MWL and 7 in Bar S. Mean baseline 25(OH)D concentrations ranged between 7 and 27 ng/ml in OB, 15-29 ng/ml in MWL and 15-24 ng/ml in Bar S. In OB (Total N 2036 participants), vitamin D doses of 1600-4000 IU/d increased mean 25(OH)D concentrations to ≥30 ng/ml. Based on three trials during MWL (Total N 359 participants), vitamin D doses of 1200-4600 IU/d for 12 months increased 25(OH)D concentration to ≥30 ng/ml. In Bar S (Total N 615 participants), doses ≥2000 IU/d were needed to reach 30 ng/ml. The change in 25(OH)D concentration was inversely proportional to the administered dose, and to BMI and baseline level with doses of 600-3000 IU/day. With these doses, the change in 25(OH)D concentration [Δ25(OH)D] per 100 IU/d was 0.5-1.2 ng/ml. Three trials assessed bone mineral density as a primary outcome, but only one of them showed a protective effect of vitamin D against bone loss at all sites post-Bar S. There was no effect of vitamin D on weight loss. Data on extra-skeletal parameters, namely glycemic and vascular indices were mostly identified in OB, and findings were inconsistent. In conclusion, Vitamin D doses ≥1600-2000 IU/d may be needed to reach a 25(OH)D concentration of 30 ng/ml in obese individuals and following bariatric surgery. The optimal concentration in this population is unknown, and whether the above doses protect against weight loss induced bone loss and fractures still needs to be confirmed. There is no clear evidence for a beneficial effect of vitamin D supplementation on cardio-metabolic parameters in obese individuals, and data on such parameters with weight loss are very scarce. Well-designed long term RCTs assessing the effect of vitamin D supplementation during weight loss on patient important outcomes are needed.

The role of vitamin D in adipogenesis

Vitamin D, a secosteroid predominately obtained by endogenous production, has in recent years been linked to obesity and its comorbidities. The purpose of this review is to draw conclusions from animal and human studies on the effects of vitamin D on adipogenesis to identify the molecular links between vitamin D and obesity. The information presented herein was obtained from 4 databases (PubMed, CINAHL, Cochrane Library, Scopus) using predefined search terms, as well as research literature and other reviews. The effects of vitamin D on adipogenesis have been researched in several animal models, and the majority of these studies suggest vitamin D plays an inhibitory role in adipogenesis. Studies into vitamin D status and obesity in humans are limited, with the majority being observational epidemiological studies that provide no conclusions on cause and effect or clear links on the molecular mechanisms. The few cell culture and supplementation studies that have investigated adipogenesis in human cells indicate that, in contrast to findings from rodent studies, vitamin D is proadipogenic. There is insufficient evidence to determine whether 1) vitamin D deficiency is associated with a lean or obese phenotype, 2) vitamin D deficiency is a consequence of obesity, or (3) the effects of vitamin D on fat tissue are due to interactions with calcium.

Vitamin D: not just the bone. Evidence for beneficial pleiotropic extraskeletal effects

Vitamin D is a fat-soluble vitamin and a steroid hormone that plays a central role in maintaining calcium-phosphorus and bone homeostasis in close interaction with parathyroid hormone, acting on its classical target tissues, namely, bone, kidney, intestine, and parathyroid glands. However, vitamin D endocrine system regulates several genes (about 3 % of the human genome) involved in cell differentiation, cell-cycle control, and cell function and exerts noncalcemic/pleiotropic effects on extraskeletal target tissues, such as immune and cardiovascular system, pancreatic endocrine cells, muscle, and adipose tissue. Several studies have demonstrated the role of vitamin D supplementation in the prevention/treatment of various autoimmune diseases and improvement of glucose metabolism, muscle, and adipose tissue function. Hence, this review aims to elucidate the effects of vitamin D on extraskeletal target tissues and to investigate the potential therapeutic benefit of vitamin D supplementation among a broad group of pathological conditions, especially with regard to metabolic and autoimmune diseases. In addition, we focused on the best daily intakes and serum levels of vitamin D required for extraskeletal benefits which, even if still controversial, appear to be higher than those widely accepted for skeletal effects.