A scoping review shows that no single existing risk of bias assessment tool considers all sources of bias for cross-sectional studies.

OBJECTIVE: Different tools to assess the potential risk of bias (RoB) for cross-sectional studies have been developed, but it is unclear whether all pertinent bias concepts are addressed. We aimed to identify RoB concepts applicable to cross-sectional research validity and to explore coverage for each in existing appraisal tools. STUDY DESIGN AND SETTING: This scoping review followed the Joanna Briggs Institute methodology. We included records of any study design describing or reporting methods, concepts or tools used to consider RoB in health research reported to be descriptive/ prevalence survey or analytic/association (cross-sectional) study designs. Synthesis included quantitative and qualitative analysis. RESULTS: Of the 4,556 records screened, 90 were selected for inclusion; 67 (74%) described the development of, or validation process for, appraisal tools, 15 (17%) described methodological content or theory relevant to RoB for cross-sectional studies and 8 (9%) records of methodological systematic reviews. Review of methodological reports identified important RoB concepts for both descriptive/prevalence and analytic/association studies. Tools identified (n=64 unique tools) were either intended to appraise quality or assess RoB in multiple study designs including cross-sectional studies (n=21; 33%) or cross-sectional designs alone (n=43; 67%). Several existing tools were modified (n=17; 27%) for application to cross-sectional studies. The RoB items most frequently addressed in the RoB tools were validity and reliability of the exposure (53%) or outcome (65%) measurement and representativeness of the study population (59%). Most tools did not consider non-response or missingness appropriately or at all. CONCLUSION: Assessing cross-sectional studies involves unique risk of bias (RoB) considerations. We identified RoB tools designed for broad applicability across various study designs as well as those specifically tailored for cross-sectional studies. However, none of the identified tools comprehensively address all potential biases pertinent to cross-sectional studies. Our findings indicate a need for continued improvement of RoB tools and suggest that the development of context-specific or more precise tools for this study design may be necessary.

Risk of bias in cross-sectional studies: Protocol for a scoping review of concepts and tools.

Cross-sectional studies are commonly used to study human health and disease, but are especially susceptible to bias. This scoping review aims to identify and describe available tools to assess the risk of bias (RoB) in cross-sectional studies and to compile the key bias concepts relevant to cross-sectional studies into an item bank. Using the JBI scoping review methodology, the strategy to locate relevant RoB concepts and tools is a combination of database searches, prospective review of PROSPERO registry records; and consultation with knowledge users and content experts. English language records will be included if they describe tools, checklists, or instruments which describe or permit assessment of RoB for cross-sectional studies. Systematic reviews will be included if they consider eligible RoB tools or use RoB tools for RoB of cross-sectional studies. All records will be independently screened, selected, and extracted by one researcher and checked by a second. An analytic framework will be used to structure the extraction of data. Results for the scoping review are pending. Results from this scoping review will be used to inform future selection of RoB tools and to consider whether development of a new RoB tool for cross-sectional studies is needed.

Perspective: Human Milk Composition and Related Data for National Health and Nutrition Monitoring and Related Research.

National health and nutrition monitoring is an important federal effort in the United States and Canada, and the basis for many of their nutrition and health policies. Understanding of child exposures through human milk (HM) remains out of reach due to lack of current and representative data on HM's composition and intake volume. This article provides an overview of the current national health and nutrition monitoring activities for HM-fed children, HM composition (HMC) and volume data used for exposure assessment, categories of potential measures in HM, and associated variability factors. In this Perspective, we advocate for a framework for collection and reporting of HMC data for national health and nutrition monitoring and programmatic needs, including a shared vision for a publicly available Human Milk Composition Data Repository (HMCD-R) to include essential metadata associated with HMC. HMCD-R can provide a central, integrated platform for researchers and public health officials for compiling, evaluating, and sharing HMC data. The compiled compositional and metadata in HMCD-R would provide pertinent measures of central tendency and variability and allow use of modeling techniques to approximate compositional profiles for subgroups, providing more accurate exposure assessments for purposes of monitoring and surveillance. HMC and related metadata could facilitate understanding the complexity and variability of HM composition, provide crucial data for assessment of infant and maternal nutritional needs, and inform public health policies, food and nutrition programs, and clinical practice guidelines.

A Bayesian method for identifying associations between response variables and bacterial community composition.

Determining associations between intestinal bacteria and continuously measured physiological outcomes is important for understanding the bacteria-host relationship but is not straightforward since abundance data (compositional data) are not normally distributed. To address this issue, we developed a fully Bayesian linear regression model (BRACoD; Bayesian Regression Analysis of Compositional Data) with physiological measurements (continuous data) as a function of a matrix of relative bacterial abundances. Bacteria can be classified as operational taxonomic units or by taxonomy (genus, family, etc.). Bacteria associated with the physiological measurement were identified using a Bayesian variable selection method: Stochastic Search Variable Selection. The output is a list of inclusion probabilities ([Formula: see text]) and coefficients that indicate the strength of the association ([Formula: see text]) for each bacterial taxa. Tests with simulated communities showed that adopting a cut point value of [Formula: see text] ≥ 0.3 for identifying included bacteria optimized the true positive rate (TPR) while maintaining a false positive rate (FPR) of ≤ 5%. At this point, the chances of identifying non-contributing bacteria were low and all well-established contributors were included. Comparison with other methods showed that BRACoD (at [Formula: see text] ≥ 0.3) had higher precision and a higher TPR than a commonly used center log transformed LASSO procedure (clr-LASSO) as well as higher TPR than an off-the-shelf Spike and Slab method after center log transformation (clr-SS). BRACoD was also less likely to include non-contributing bacteria that merely correlate with contributing bacteria. Analysis of a rat microbiome experiment identified 47 operational taxonomic units that contributed to fecal butyrate levels. Of these, 31 were positively and 16 negatively associated with butyrate. Consistent with their known role in butyrate metabolism, most of these fell within the Lachnospiraceae and Ruminococcaceae. We conclude that BRACoD provides a more precise and accurate method for determining bacteria associated with a continuous physiological outcome compared to clr-LASSO. It is more sensitive than a generalized clr-SS algorithm, although it has a higher FPR. Its ability to distinguish genuine contributors from correlated bacteria makes it better suited to discriminating bacteria that directly contribute to an outcome. The algorithm corrects for the distortions arising from compositional data making it appropriate for analysis of microbiome data.

NUQUEST-NUtrition QUality Evaluation Strengthening Tools: development of tools for the evaluation of risk of bias in nutrition studies.

BACKGROUND: Dietary exposure assessments are a critical issue in evaluating human nutrition studies; however, nutrition-specific criteria are not consistently included in existing bias assessment tools. OBJECTIVES: Our objective was to develop a set of risk of bias (RoB) tools that integrated nutrition-specific criteria into validated generic assessment tools to address RoB issues, including those specific to dietary exposure assessment. METHODS: The Nutrition QUality Evaluation Strengthening Tools (NUQUEST) development and validation process included 8 steps. The first steps identified 1) a development strategy; 2) generic assessment tools with demonstrated validity; and 3) nutrition-specific appraisal issues. This was followed by 4) generation of nutrition-specific items and 5) development of guidance to aid users of NUQUEST. The final steps used established ratings of selected studies and feedback from independent raters to 6) assess reliability and validity; 7) assess formatting and usability; and 8) finalize NUQUEST. RESULTS: NUQUEST is based on the Scottish Intercollegiate Guidelines Network checklists for randomized controlled trials, cohort studies, and case-control studies. Using a purposive sample of 45 studies representing the 3 study designs, interrater reliability was high (Cohen's κ: 0.73; 95% CI: 0.52, 0.93) across all tools and at least moderate for individual tools (range: 0.57-1.00). The use of a worksheet improved usability and consistency of overall interrater agreement across all study designs (40% without worksheet, 80%-100% with worksheet). When compared to published ratings, NUQUEST ratings for evaluated studies demonstrated high concurrent validity (93% perfect or near-perfect agreement). Where there was disagreement, the nutrition-specific component was a contributing factor in discerning exposure methodological issues. CONCLUSIONS: NUQUEST integrates nutrition-specific criteria with generic criteria from assessment tools with demonstrated reliability and validity. NUQUEST represents a consistent and transparent approach for evaluating RoB issues related to dietary exposure assessment commonly encountered in human nutrition studies.

Inadequate vitamin D status is associated with lower food plus supplemental intake of vitamin D in children of South Asian ethnicity living in the National Capital Region of Canada.

Vitamin D status, measured in a Vitamin D Standardization Program certified laboratory, was assessed among children of South Asian and European ethnicity living in the national capital region of Canada to explore factors that may account for inadequate status. Demographic information, dietary and supplemental vitamin D over 30 d prior to measurement of serum 25-hydroxyvitamin D (25OHD), and anthropometry were measured (age 6.0-18.9 y; n = 58/group; February-March 2015). No group related differences in age, height and body mass index (BMI) Z-scores or in food vitamin D intakes were observed. Standardized serum 25OHD was lower in South Asian children (mean ± SD: 39.0 ± 16.8 nmol/L vs. European: 58.4 ± 15.8 nmol/L). A greater proportion of South Asian children had serum 25OHD <40 nmol/L (56.9 vs. 8.6%, P < 0.0001) and fewer took supplements (31 vs. 50%, P = 0.0389). In a multi-factorial model (r2 = 0.54), lower vitamin D status was associated with overweight/obese BMI and older age (14-18 y); no interaction with ethnicity was observed. Lower vitamin D status was associated with lower total vitamin D intake only in South Asian children. This study reinforces the importance of public health actions towards meeting vitamin D intake recommendations among those of high-risk deficiency. Novelty: A higher proportion of South Asian vs. European children had inadequate vitamin D status. Lower vitamin D status was associated with a BMI in the overweight/obese range. Lower vitamin D status was associated with lower total vitamin D intake in South Asian but not European children.

Early prenatal use of a multivitamin diminishes the risk for inadequate vitamin D status in pregnant women: results from the Maternal-Infant Research on Environmental Chemicals (MIREC) cohort study.

BACKGROUND: Reports on the adequacy of vitamin D status of pregnant women are not available in Canada. OBJECTIVES: The objectives of this study were to examine vitamin D status across pregnancy and identify the correlates of vitamin D status of pregnant women in Canada. METHODS: Pregnant women (≥18 years) from 6 provinces (2008-2011) participating in a longitudinal cohort were studied. Sociodemographic data, obstetrical histories, and dietary and supplemental vitamin D intakes were surveyed. Plasma 25-hydroxyvitamin D (25OHD) was measured using an immunoassay standardized to LC-MS/MS from samples collected during the first (n = 1905) and third trimesters (n = 1649) and at delivery (n = 1543). The proportion of women with ≥40 nmol/L of plasma 25OHD (adequate status) was estimated at each time point, and factors related to achieving this cut point were identified using repeated-measures logistic regression. Differences in 25OHD concentrations across trimesters and at delivery were tested a using repeated-measures ANOVA with a post hoc Tukey's test. RESULTS: In the first trimester, 93.4% (95% CI: 92.3%-94.5%) of participants had 25OHD ≥40 nmol/L. The mean plasma 25OHD concentration increased from the first to the third trimester and then declined by delivery (69.8 ± 0.5 nmol/L, 78.6 ± 0.7 nmol/L, and 75.7 ± 0.7 nmol/L, respectively; P < 0.0001). A lack of multivitamin use early in pregnancy reduced the odds of achieving 25OHD ≥40 nmol/L (ORadj = 0.33; 95% CI: 0.25-0.42) across all time points. Factors associated with not using a prenatal multivitamin included multiparity (ORadj = 2.08; 95% CI: 1.42-3.02) and a below-median income (ORadj = 1.39; 95% CI: 1.02-1.89). CONCLUSIONS: The results from this cohort demonstrate the importance of early multivitamin supplement use to achieve an adequate vitamin D status in pregnant women.

Calcium exacerbates the inhibitory effects of phytic acid on zinc bioavailability in rats.

BACKGROUND: Complementary feeding of breastfed infants with foods high in bioavailable zinc (Zn) can help meet physiological requirements for Zn. Some infant cereals contain high concentrations of phytic acid (PA) and calcium (Ca) that may reduce absorbable Zn. OBJECTIVES: This study measured PA, Zn and Ca concentrations in selected infant cereals sold in Canada and investigated the effects of dietary PA and Ca at concentrations present in infant cereals on Zn bioavailability in rats. METHODS AND RESULTS: Male Sprague-Dawley rats (36-day old) were fed a control diet containing normal Zn (29.1 mg/kg) and Ca (4.95 g/kg) or six test diets (n = 12/diet group). Test diets were low in Zn (8.91-9.74 mg/kg) and contained low (2.16-2.17 g/kg), normal (5.00-5.11 g/kg) or high (14.6-14.9 g/kg) Ca without or with added PA (8 g/kg). After 2 weeks, rats were killed and Zn status of the rats was assessed. PA, Zn and Ca concentrations in infant cereals (n = 20) differed widely. PA concentrations ranged from undetectable to 16.0 g/kg. Zn and Ca concentrations ranged from 7.0-29.1 mg/kg and 0.8-13.4 g/kg, respectively. The [PA]/[Zn] and [PA × Ca]/[Zn] molar ratios in infants cereals with detectable PA (16 of 20 cereals) ranged from 22-75 and 0.9-14.9 mol/kg, respectively, predicting low Zn bioavailability. Body weight, body composition (lean and fat mass), right femur weight and length measurements and Zn concentrations in serum and femur indicated that diets higher in Ca had a more pronounced negative effect on Zn status of rats fed a PA-supplemented diet. Addition of PA to the diet had a greater negative effect on Zn status when Ca concentration in the diet was higher. CONCLUSION: These results show that, in rats, higher concentrations of dietary Ca and PA interact to potentiate a decrease in bioavailable Zn and may suggest lower Zn bioavailability in infant cereals with higher PA and Ca concentrations.

Fructooligosaccharides and wheat bran fed at similar fermentation levels differentially affect the expression of genes involved in transport, signaling, apoptosis, cell proliferation, and oncogenesis in the colon epithelia of healthy Fischer 344 rats.

The influence of the source of fermentable material (FM) on the luminal concentrations of their end products and its effects on colon cell metabolism and disease susceptibility is not well characterized. We hypothesized that total fermentation but not the source (type) of FM would be the main factor in determining cellular /molecular outcomes in the healthy colon epithelia. The main aim of this study was to elucidate the role of two different sources of FM, fructooligosaccharides (FOS) and wheat bran (WB), on the expression of genes involved in short chain fatty acid (SCFA) transport, G-protein signaling, apoptosis, cell proliferation and oncogenesis in colon epithelia of healthy rats. Male Fischer 344 rats (n = 10/group) were fed AIN-93G control (0% FM) or experimental diets containing WB (~1%, 2%, or 5% FM) or FOS (~2%, 5%, or 8% FM). Rats were killed after 6 weeks and the colon mucosa was assessed for the expression of target genes using real-time quantitative polymerase chain reaction. By comparison to the control, dose-related changes of mRNA levels were found in rats fed FOS-based diets, including: (a) upregulation of three SCFA transporters (Smct2, Mct1 and Mct4) but downregulation of Mct2, (b) upregulation of Gpr109a and downregulation of Gpr120, Gpr43, Gprc5a, Rgs2 and Rgs16, (c) upregulation of apoptosis-related genes including Bcl2, Bcl2-like 1, Bak1, Caspase 3, Caspase 8 and Caspase 9, (d) downregulation of the oncogenes and metastasis genes Ros1, Fos, Cd44, Fn1 and Plau, and (e) downregulation of several genes involved in cellular proliferation including Hbegf, Hoxb13, Cgref1, Wfdc1, Tgm3, Fgf7, Nov and Lumican. In contrast, rats fed WB-based diets resulted in dose-related upregulation of mRNA levels of Smct2, Rgs16, Gprc5a, Gpr109a, Bcl2-like 1, Caspase 8, and Fos. Additionally, different gene expression responses were observed in rats fed FOS and WB at 2% and 5% FM. Over all, these gene changes elicited by FOS and WB were independent of the expression of the tumor suppressor Tp53. These results suggest that fermentation alone is not the sole determinant of gene responses in the healthy rat colon.

Impact of ß2-1 fructan on faecal community change: results from a placebo-controlled, randomised, double-blinded, cross-over study in healthy adults.

Healthy adults (n 30) participated in a placebo-controlled, randomised, double-blinded, cross-over study consisting of two 28 d treatments (ß2-1 fructan or maltodextrin; 3×5 g/d) separated by a 14-d washout. Subjects provided 1 d faecal collections at days 0 and 28 of each treatment. The ability of faecal bacteria to metabolise ß2-1 fructan was common; eighty-seven species (thirty genera, and four phyla) were isolated using anaerobic medium containing ß2-1 fructan as the sole carbohydrate source. ß2-1 fructan altered the faecal community as determined through analysis of terminal restriction fragment length polymorphisms and 16S rRNA genes. Supplementation with ß2-1 fructan reduced faecal community richness, and two patterns of community change were observed. In most subjects, ß2-1 fructan reduced the content of phylotypes aligning within the Bacteroides, whereas increasing those aligning within bifidobacteria, Faecalibacterium and the family Lachnospiraceae. In the remaining subjects, supplementation increased the abundance of Bacteroidetes and to a lesser extent bifidobacteria, accompanied by decreases within the Faecalibacterium and family Lachnospiraceae. ß2-1 Fructan had no impact on the metagenome or glycoside hydrolase profiles in faeces from four subjects. Few relationships were found between the faecal bacterial community and various host parameters; Bacteroidetes content correlated with faecal propionate, subjects whose faecal community contained higher Bacteroidetes produced more caproic acid independent of treatment, and subjects having lower faecal Bacteroidetes exhibited increased concentrations of serum lipopolysaccharide and lipopolysaccharide binding protein independent of treatment. We found no evidence to support a defined health benefit for the use of ß2-1 fructans in healthy subjects.

An Analysis of Factors Associated with 25-Hydroxyvitamin D Levels in White and Non-White Canadians.

Vitamin D status was assessed in 19-79 year old whites (8351 participants of European ancestry) and non-whites (1840 participants encompassing all other ancestries) from cycles 1 to 3 (years 2007-2013) of the Canadian Health Measures Survey. Status was assessed using the U.S. Institute of Medicine (IOM) 25-hydroxyvitamin D [25(OH)D] cut point values of 30 and 40 nmol/L. Overall, median 25(OH)D concentrations were significantly higher in whites [58.9 (28.6, 100.1) nmol/L; 5th and 95th percentile] compared with non-whites [43.5 (19.0, 83.2); P < 0.001]. Values were higher in females [58.5 (27.5, 101.3) nmol/L] when compared with males [53.5 (24.2, 92.7) nmol/L] and increased with age. Non-whites were more likely to have 25(OH)D values below IOM established cut points for optimum bone health with 20.1 (16.0, 24.2) and 42.2% (36.8, 47.7) of non-whites having serum 25(OH)D concentrations <30 and <40 nmol/L, respectively. The corresponding values for whites were 5.9 (4.6, 7.2) and 16.1% (14.0, 18.3). Values were lower during the first quarter when compared with the third quarter. Supplement intake was an important factor in determining 25(OH)D levels, but it did not alone account for the difference in status. Equivalent increases in 25(OH)D levels were observed in whites and non-whites during the summer months, suggesting there was no functional difference in sun exposure response. It is apparent that a complex interaction of factors affect 25(OH)D values in free-living Canadians.

Baseline Assessment of 25-Hydroxyvitamin D Reference Material and Proficiency Testing/External Quality Assurance Material Commutability: A Vitamin D Standardization Program Study.

The Vitamin D Standardization Program (VDSP) coordinated a study in 2012 to assess the commutability of reference materials and proficiency testing/external quality assurance materials for total 25-hydroxyvitamin D [25(OH)D] in human serum, the primary indicator of vitamin D status. A set of 50 single-donor serum samples as well as 17 reference and proficiency testing/external quality assessment materials were analyzed by participating laboratories that used either immunoassay or LC-MS methods for total 25(OH)D. The commutability test materials included National Institute of Standards and Technology Standard Reference Material 972a Vitamin D Metabolites in Human Serum as well as materials from the College of American Pathologists and the Vitamin D External Quality Assessment Scheme. Study protocols and data analysis procedures were in accordance with Clinical and Laboratory Standards Institute guidelines. The majority of the test materials were found to be commutable with the methods used in this commutability study. These results provide guidance for laboratories needing to choose appropriate reference materials and select proficiency or external quality assessment programs and will serve as a foundation for additional VDSP studies.

Baseline Assessment of 25-Hydroxyvitamin D Assay Performance: A Vitamin D Standardization Program (VDSP) Interlaboratory Comparison Study.

The Vitamin D Standardization Program (VDSP) coordinated an interlaboratory study to assess the comparability of measurements of total 25-hydroxyvitamin D [25(OH)D] in human serum, which is the primary marker of vitamin D status. A set of 50 individual donor samples were analyzed by 15 different laboratories representing national nutrition surveys, assay manufacturers, and clinical and/or research laboratories to provide results for total 25(OH)D using both immunoassays (IAs) and LC tandem MS (MS/MS). The results were evaluated relative to bias compared with the target values assigned based on a combination of measurements at Ghent University (Belgium) and the U.S. National Institute of Standards and Technology using reference measurement procedures for the determination of 25(OH)D2 and 25(OH)D3. CV and mean bias for each laboratory and assay platform were assessed and compared with previously established VDSP performance criteria, namely CV ≤ 10% and mean bias ≤ 5%. Nearly all LC-MS/MS results achieved VDSP criteria, whereas only 50% of IAs met the criterion for a ≤10% CV and only three of eight IAs achieved the ≤5% bias. These results establish a benchmark for the evaluation of 25(OH)D assay performance and standardization activities in the future.

The Vitamin D Standardization Program (VDSP) Manual for Retrospective Laboratory Standardization of Serum 25-Hydroxyvitamin D Data.

Low concentrations of total 25-hydroxyvitamin D [25(OH)D], the principal biological measure of vitamin D status, have been associated with clinical and public health outcomes. The determination of levels under which there is an increase in the risk of disease, as well as comparisons across populations, have been difficult to establish due the large assay variability in measuring 25(OH)D. Accordingly, the Vitamin D Standardization Program (VDSP) includes the retrospective standardization of existing 25(OH)D values collected by epidemiological and clinical studies, as well as clinical trials, as one of its main objectives. We introduce methodology developed by the VDSP that can be used to standardize the measurement of time-stable analytes, including 25(OH)D, in samples that have been banked and maintained appropriately. Sample size estimation formulae are first applied to calculate the required number of banked blood samples to be reanalyzed using either of two approaches. In the first approach, existing samples are remeasured using the current measurement procedure, and an equation relating "old" to "current" measurements is obtained. A second set of sera, usually 40-50 single-donor serum samples, are measured with the current measurement procedure and an assay traceable to a reference measurement procedure and/or certified reference materials, which yields a second calibration equation. These two equations are combined to produce standardized levels from the original old values. This approach is necessary when study restrictions prevent serum samples from being shipped to an external laboratory and is illustrated with samples from the Canadian Health Measures Survey. When serum samples are permitted to be shared with other laboratories, or the study investigators can carry out the measurements with a traceable assay, a single calibration equation method is used. Existing samples are selected and remeasured using the available traceable assay. We outline the statistical theory supporting the VDSP protocol and provide implementation examples. The methods proposed are generalizable to any instance in which banked specimens have been properly prepared and stored and the analyte of interest is stable under those conditions.

Development of an Improved Standard Reference Material for Vitamin D Metabolites in Human Serum.

The National Institute of Standards and Technology (NIST) has developed Standard Reference Material (SRM) 972a Vitamin D Metabolites in Frozen Human Serum as a replacement for SRM 972, which is no longer available. SRM 972a was developed in collaboration with the National Institutes of Health's Office of Dietary Supplements. In contrast to the previous reference material, three of the four levels of SRM 972a are composed of unmodified human serum. This SRM has certified and reference values for the following 25-hydroxyvitamin D [25(OH)D] species: 25(OH)D2, 25(OH)D3, and 3-epi-25(OH)D3. The value assignment and certification process included three isotope-dilution mass spectrometry approaches, with measurements performed at NIST and at the Centers for Disease Control and Prevention (CDC). The value assignment methods employed have been modified from those utilized for the previous SRM, and all three approaches now incorporate chromatographic resolution of the stereoisomers, 25(OH)D3 and 3-epi-25(OH)D3.

Housing influences tissue cytokine levels and the fecal bacterial community structure in rats.

Immune measures and the fecal bacterial community were examined in female Biobreeding rats housed in wire bottom cages (wire) or in solid bottom cages containing hardwood chips (bedding). Housing did not affect food intake, weight gain, fecal output or fibre content, serum liver enzymes, or spleen and mesenteric lymph node immune cell populations. Bedding-housed rat feces were enriched in phylotypes aligning within the phylum Firmicutes (families Lactobacillaceae and Erysipelotrichaceae) and had a 2-fold lower content of phylotypes aligning within the phylum Bacteroidetes. Feces from bedding-housed rats also contained significantly more acetic acid and less propionic, isobutyric, valeric and isovaleric acids than those housed on wire. Bedding-housed rats had significantly higher splenic concentrations of interleukin-4 (P < 0.001). These results demonstrate that bedding can indirectly influence systemic and mucosal immune measures, potentially adding additional complexities and confounding results to nutrition studies investigating the health effects of dietary fibres.

ß2-1 Fructan supplementation alters host immune responses in a manner consistent with increased exposure to microbial components: results from a double-blinded, randomised, cross-over study in healthy adults.

ß2-1 Fructans are purported to improve health by stimulating growth of colonic bifidobacteria, increasing host resistance to pathogens and stimulating the immune system. However, in healthy adults, the benefits of supplementation remain undefined. Adults (thirteen men, seventeen women) participated in a double-blinded, placebo-controlled, randomised, cross-over study consisting of two 28-d treatments separated by a 14-d washout period. Subjects' regular diets were supplemented with ß2-1 fructan or placebo (maltodextrin) at 3×5 g/d. Fasting blood and 1-d faecal collections were obtained at the beginning and at the end of each phase. Blood was analysed for clinical, biochemical and immunological variables. Determinations of well-being and general health, gastrointestinal (GI) symptoms, regularity, faecal SCFA content, residual faecal ß2-1 fructans and faecal bifidobacteria content were undertaken. ß2-1 Fructan supplementation had no effect on blood lipid or cholesterol concentrations or on circulating lymphocyte and macrophage numbers, but significantly increased serum lipopolysaccharide, faecal SCFA, faecal bifidobacteria and indigestion. With respect to immune function, ß2-1 fructan supplementation increased serum IL-4, circulating percentages of CD282+/TLR2+ myeloid dendritic cells and ex vivo responsiveness to a toll-like receptor 2 agonist. ß2-1 Fructans also decreased serum IL-10, but did not affect C-reactive protein or serum/faecal Ig concentrations. No differences in host well-being were associated with either treatment, although the self-reported incidence of GI symptoms and headaches increased during the ß2-1 fructan phase. Although ß2-1 fructan supplementation increased faecal bifidobacteria, this change was not directly related to any of the determined host parameters.

A Spatially Continuous Model of Carbohydrate Digestion and Transport Processes in the Colon.

A spatially continuous mathematical model of transport processes, anaerobic digestion and microbial complexity as would be expected in the human colon is presented. The model is a system of first-order partial differential equations with context determined number of dependent variables, and stiff, non-linear source terms. Numerical simulation of the model is used to elucidate information about the colon-microbiota complex. It is found that the composition of materials on outflow of the model does not well-describe the composition of material in other model locations, and inferences using outflow data varies according to model reactor representation. Additionally, increased microbial complexity allows the total microbial community to withstand major system perturbations in diet and community structure. However, distribution of strains and functional groups within the microbial community can be modified depending on perturbation length and microbial kinetic parameters. Preliminary model extensions and potential investigative opportunities using the computational model are discussed.

Standardizing 25-hydroxyvitamin D values from the Canadian Health Measures Survey.

BACKGROUND: The Canadian Health Measures Survey (CHMS) is an ongoing cross-sectional national survey that includes a measure of 25-hydroxyvitamin D [25(OH)D] by immunoassay. For cycles 1 and 2, the collection period occurred approximately every 2 y, with a new sample of ∼5600 individuals. OBJECTIVE: The goal was to standardize the original 25(OH)D CHMS values in cycles 1 and 2 to the internationally recognized reference measurement procedures (RMPs) developed by the US National Institute for Standards and Technology (NIST) and Ghent University, Belgium. DESIGN: Standardization was accomplished by using a 2-step procedure. First, serum samples corresponding to the original plasma samples were remeasured by using the currently available immunoassay method. Second, 50 serum samples with known 25(OH)D values assigned by the NIST and Ghent reference method laboratories were measured by using the currently available immunoassay method. The mathematical models for each step-i.e., 1) YCurrent = XOriginal and 2) YNIST-Ghent = XCurrent -were estimated by using Deming regression, and the 2 models were solved to obtain a single equation for converting the "original" values to NIST-Ghent RMP values. RESULTS: After standardization (cycles 1 and 2 combined), the percentage of Canadians with 25(OH)D values <40 nmol/L increased from 16.4% (original) to 19.4% (standardized), and values <50 nmol/L increased from 29.0% (original) to 36.8% (standardized). The 25(OH)D standardized distributions (cycles 1 and 2 analyzed separately) were similar across age and sex groups; slightly higher values were associated with cycle 2 in the young and old. This finding contrasts with the original data, which indicated that cycle 2 values were lower for all age groups. CONCLUSION: The shifts in 25(OH)D distribution brought about by standardization indicate its importance in drawing correct conclusions about potential population deficiencies and insufficiencies and in permitting the comparison of distributions between national surveys.