Emily K. Calton

The Impact of Vitamin D Levels on Inflammatory Status: A Systematic Review of Immune Cell Studies

Chronic low-grade inflammation accompanies obesity and its related chronic conditions. Both peripheral blood mononuclear cells (PBMCs) and cell lines have been used to study whether vitamin D has immune modulating effects; however, to date a detailed systematic review describing the published evidence has not been completed. We therefore conducted a systematic review on the effect of vitamin D on the protein expression and secretion of inflammatory markers by human-derived immune cells. The review was registered at the International Prospective Register for Systematic Reviews (PROSPERO, Registration number CRD42015023222). A literature search was conducted using Pubmed, Science Direct, Scopus, Web of Science and Medline. The search strategy used the following search terms: Vitamin D or cholecalciferol or 1,25-dihydroxyvitamin or 25-hydroxy-Vitamin D and Inflam* or cytokine* and supplement* or cell*. These terms were searched in the abstract, title and keywords. Inclusion criteria for study selection consisted of human-derived immune cell lines or cellular studies where PBMCs were obtained from humans, reported in the English language, and within the time period of 2000 to 2015. The selection protocol was mapped according to PRISMA guidelines. Twenty three studies (7 cell line and 16 PBMCs studies) met our criteria. All studies selected except one used the active metabolite 1,25(OH)2, with one study using cholecalciferol and two studies also using 25(OH)D. Four out of seven cell line studies showed an anti-inflammatory effect where suppression of key markers such as macrophage chemotactic protein 1, interleukin 6 and interleukin 8 were observed. Fourteen of sixteen PBMC studies also showed a similar anti-inflammatory effect based on common inflammatory endpoints. Mechanisms for such effects included decreased protein expression of toll-like receptor-2 and toll-like receptor-4; lower levels of phosphorylated p38 and p42/42; reduced expression of phosphorylated signal transducer and activator of transcription 5 and decreased reactive oxygen species. This review demonstrates that an anti-inflammatory effect of vitamin D is a consistent observation in studies of cell lines and human derived PBMCs.

Certain dietary patterns are beneficial for the metabolic syndrome: reviewing the evidence

The metabolic syndrome (MetS) is a global public health issue of increasing magnitude. The Asia-Pacific region is expected to be hardest hit due to large population numbers, rising obesity, and insulin resistance (IR). This review assessed the protective effects of dietary patterns and their components on MetS. A literature search was conducted using prominent electronic databases and search terms that included in combination: diet, dietary components, dietary patterns, and metabolic syndrome. Articles were restricted to prospective studies and high quality randomized controlled trials that were conducted on humans, reported in the English language, and within the time period of 2000 to 2012. Traditional factors such as age, gender, physical activity, and obesity were associated with risk of MetS; however, these potential confounders were not always accounted for in study outcomes. Three dietary patterns emerged from the review; a Mediterranean dietary pattern, dietary approaches to stop hypertension diet, and the Nordic Diet. Potential contributors to their beneficial effects on prevalence of MetS or reduction in MetS components included increases in fruits, vegetables, whole grains, dairy and dairy components, calcium, vitamin D, and whey protein, as well as monounsaturated fatty acids, and omega-3 fatty acids. Additional prospective and high quality randomized controlled trial studies that investigate Mediterranean dietary pattern, the dietary approaches to stop hypertension diet, and the Nordic Diet would cement the protective benefits of these diets against the MetS.

Vitamin D supplementation and body weight status: a systematic review and meta-analysis of randomized controlled trials

Vitamin D is anticipated to have many extra‐skeletal health benefits. We questioned whether supplementation with the vitamin influenced body weight and composition. A systematic review and meta‐analysis was conducted on high‐quality, randomized controlled trials (RCTs) that had supplemented vitamin D without imposing any caloric restriction. Eighteen trials reporting either body weight, body mass index (BMI), fat mass (FM), percentage fat mass (%FM) or lean body mass (LBM) met our criteria. Twelve studies provided the required data for the meta‐analysis. Vitamin D supplementation did not influence the standardized mean difference (SMD) for body weight, FM, %FM or LBM. A small but non‐significant decrease in BMI (SMD = −0.097, 95% confidence interval: [−0.210, 0.016], P = 0.092) was observed. Meta‐regression confirmed that neither the absolute vitamin D status achieved nor its change from baseline influenced the SMD of any obesity measure. However, increasing age of the subjects predicted a shift in the SMD for FM towards the placebo treatment, whereas a greater percentage of women in these studies favoured a decrease in FM following vitamin D. Vitamin D supplementation did not decrease measures of adiposity in the absence of caloric restriction. A potential confounding by age and gender was encountered.

The potential regulatory role of vitamin D in the bioenergetics of inflammation.

Purpose of reviewThe extraskeletal health benefits of vitamin D still need scientific endorsement. Obesity and related chronic diseases are pathogenically linked by inflammation, which carries a considerable energetic cost. Recent techniques for the determination of the bioenergetic demand of inflammation, offer an avenue to cement the regulatory role of vitamin D in this process. Recent findingsNuclear vitamin D receptors may be translocated into mitochondria of certain cell types, opening up a pathway for direct action on cellular bioenergetics. Classical M1 (inflammatory)/M2(anti-inflammatory) phenotypes can vary with the clinical context. M2 macrophages do not always depend on oxidative metabolism/fatty acid oxidation. Newer methodologies offer real-time bioenergetic measurements that can be used as an index of metabolic health. SummaryVitamin D may prove to be a therapeutic agent for inflammation of chronic disease and understanding its role in cellular bioenergetics may offer a diagnostic/prognostic indicator of its action.

Calcium and Vitamin D in Obesity and Related Chronic Disease.

There is a pandemic of lifestyle-related diseases. In both developed and lesser developed countries of the world, an inadequacy of calcium intake and low vitamin D status is common. In this chapter, we explore a mechanistic framework that links calcium and vitamin D status to chronic conditions including obesity, systemic inflammation, endothelial dysfunction, dyslipidemia and cardiovascular disease, and type 2 diabetes mellitus. We also update the available clinical evidence, mainly from randomized controlled trials, to provide a synthesis of evidence in favor or against these hypotheses. There is consistent data to support calcium increasing whole body fat oxidation and increasing fecal fat excretion, while there is good cellular evidence for vitamin D reducing inflammation. Clinical trials support a marginal reduction in circulating lipids and some meta-analysis support an increase in insulin sensitivity following vitamin D. However, these mechanistic pathways and intermediate biomarkers of disease do not consistently transcribe into measurable health outcomes. Cementing the benefits of calcium and vitamin D for extraskeletal health needs a reexamination of the target 25(OH)D level to be achieved and the minimum duration of future trials.

The impact of cryopreservation on human peripheral blood leucocyte bioenergetics.

Circulating immune cells are considered a source for biomarkers in health and disease, since they are exposed to nutritional, metabolic and immunological stimuli in the vasculature. Cryopreservation of leucocytes is routinely used for long-term storage and determination of phenotypic/functional changes at a later date. Exploring the role of bioenergetics and mitochondrial (dys)function in leucocytes is often examined by using freshly isolated cells. The aim of the pilot study described herein was to assess leucocyte bioenergetics in cryopreserved cells. Leucocytes were isolated from whole blood, counted and frozen in liquid nitrogen (LN2) for a period of 3 months. Cells were thawed at regular intervals and bioenergetic analysis performed using the Seahorse XFe96 flux analyser. Cryogenic storage reduced cell viability by 20%, but cell bioenergetic responses were largely intact for up to 1 month storage in LN2. However, after 1 month storage, mitochondrial function was impaired as reflected by decreasing basal respiration, ATP production, maximum (MAX) respiration, reserve capacity and coupling efficiency. Conversely, glycolytic activity was increased after 1 month, most notably the enhanced glycolytic response to 25 mM glucose without any change in glycolytic capacity. Finally, calculation of bioenergetic health index (BHI) demonstrated that this potential diagnostic parameter was sensitive to cryopreservation. The present study has demonstrated for the first time that cryopreservation of primary immune cells modified their metabolism in a time-dependent fashion, indicated by attenuated aerobic respiration and enhanced glycolytic activity. Taken together, we recommend caution in the interpretation of bioenergetic responses or BHI in cryopreserved samples.

Calcium and vitamin D in the regulation of energy balance: where do we stand?

There is a pandemic of obesity and associated chronic diseases. Dietary calcium and vitamin D have many extra-skeletal roles in human health. In this review we have summarized the current understanding of their influence on human energy balance by examining the epidemiological, clinical, animal, cellular and molecular evidence. We opine that while calcium and vitamin D are functional nutrients in the battle against obesity, there is a need for prospective human trials to tilt the balance of evidence in favour of these nutrients.

Factors determining the risk of the metabolic syndrome: is there a central role for adiponectin|[quest]|

Background and objectives:The pathogenesis of the metabolic syndrome (MetS) is not well understood. This review is based on the hypothesis that both traditional and emerging risk factors act through adiponectin.Subjects and methods:We conducted a search of the literature using prominent electronic databases and search terms that included in combination: adiponectin, diet, dietary patterns, exercise, metabolic rate, MetS and testosterone. Articles were restricted to studies conducted on adult humans, reported in English and within the time period 2000–2012.Results and conclusions:Both traditional and emerging risk factors associated with the MetS show some evidence of exerting their influence through adiponectin. High-quality randomized controlled trials that alter adiponectin levels are required to further corroborate this hypothesis.

The bioenergetics of inflammation: insights into obesity and type 2 diabetes

Diabetes mellitus is one of the most common chronic metabolic disorders worldwide, and its incidence in Asian countries is alarmingly high. Type 2 diabetes (T2DM) is closely associated with obesity, and the staggering rise in obesity is one of the primary factors related to the increased frequency of T2DM. Low-grade chronic inflammation is also accepted as an integral metabolic adaption in obesity and T2DM, and is believed to be a major player in the onset of insulin resistance. However, the exact mechanism(s) that cause a persistent chronic low-grade infiltration of leukocytes into insulin-target tissues such as adipose, skeletal muscle and liver are not entirely known. Recent developments in the understanding of leukocyte metabolism have revealed that the inflammatory polarization of immune cells, and consequently their immunological function, are strongly connected to their metabolic profile. Therefore, it is hypothesized that dysfunctional immune cell metabolism is a central cellular mechanism that prevents the resolution of inflammation in chronic metabolic conditions such as that observed in obesity and T2DM. The purpose of this review is to explore the metabolic demands of different immune cell types, and identify the molecular switches that control immune cell metabolism and ultimately function. Understanding of these concepts may allow the development of interventions that can correct immune function and may possibly decrease chronic low-grade inflammation in humans suffering from obesity and T2DM. We also review the latest clinical techniques used to measure metabolic flux in primary leukocytes isolated from obese and T2DM patients.

The impact of cholecalciferol supplementation on the systemic inflammatory profile: a systematic review and meta-analysis of high-quality randomized controlled trials

Causal links between vitamin D status [25(OH)D] and systemic inflammation were examined through a systematic review of randomized controlled trials (RCTs). Selected RCTs were ⩾12 weeks, conducted in adults free of acute inflammatory disease, and of high-quality (Jadad score ⩾3). Of 14 studies that met our criteria, 9 studies (15 study arms) permitted extraction of data. There was no effect on the weighted mean difference (WMD) of IL-6 (WMD (95% confidence interval)=0.1, (−0.166, 0.366) pg/ml, P=0.462) or C-reactive protein (CRP) (WMD=−0.324, (−1.007, 0.359) mg/l, P=0.352). Subgroup analyses of trials achieving ⩾80 nmol/l indicated a trend for lower CRP (WMD=−0.834, (−1.726, 0.058) mg/l, P=0.067), however heterogeneity was significant (I2=66.7%, P=0.017). Studies employing a low dose (<1000 IU/d) showed increased CRP (WMD=0.615, (0.132, 1.098), P=0.013). In contrast, ⩾1000 IU/d had a favourable effect on CRP (WMD=−0.939, (−1.805, −0.073), P=0.034) but heterogeneity was significant (I2=61.3%, P=0.017). Meta-regression indicated that older age predicted a significant decrease in IL−6 (β=−0.02, (−0.034, −0.006) pg/ml, P=0.013) and CRP (β=−0.06, (−0.103, −0.017), P=0.01), whereas a greater percentage of females (β=0.027, (0.011, 0.044), P=0.004) and longer study duration independently predicted a higher WMD for CRP (β=0.049, (0.018, 0.079), P=0.005). Available high-quality RCTs did not support a beneficial effect of cholecalciferol on systemic IL-6 and CRP. Future studies should consider the confounding effects of age, gender and study duration, while possibly targeting an achieved 25(OH)D ⩾80 nmol/l.