Laboratory issues: use of nutritional biomarkers

Assessment of Nutritional Status and Correlation of Factors With Body Mass Index of Cancer Patients: A Cross-Sectional Study

BACKGROUND

Decreased diet intake and malnourishment have profound implications on cancer patients' quality of life and survival. Malnutrition increases the risk of postoperative complications, increases hospital length stays, reduces patient's tolerance to radiation and chemotherapy treatment, and results in poor response to treatment. In the present study, we intended to assess the nutritional status of cancer patients and find the correlation of body mass index with anthropometric and blood parameters.

MATERIAL & METHODS

The study was prospective and cross-sectional, and 104 patients with newly diagnosed solid tumors were included. Patient demographics, symptoms, and anthropometric and blood parameters were collected. The correlation was estimated with Pearson's correlation coefficient. A p-value of less than 0.05 was considered significant.

RESULTS

The association between stages of the disease, dental status, type of diet, and BMI was p=0.701, 0.216, and 0.422, respectively, and was not statistically significant. The anthropometric parameters mid upper arm circumference (MUAC cm), mid arm circumference (MAC cm), and triceps skinfold thickness (TSF mm) correlated with body mass index (BMI kg/m2) and had statistically significant p values of 0.0001, 0.0001, and 0.033, respectively. The correlation was assessed between hemoglobin, red cell distribution width, neutrophil-to-lymphocyte ratio, and serum albumin levels with BMI, but except for albumin (p=0.05), no other blood parameter correlated.

CONCLUSION

Nutritional assessment is vital in recognizing patients at risk of treatment-associated complications and poor responders to treatment. In this study, BMI correlated with anthropometric parameters MUAC, MAMC, and TSF. Baseline dietary assessments of patients will help focus on the nutritional build-up of patients before starting treatment.

Serum biomarkers for nutritional status as predictors in COVID-19 patients before and after vaccination

The aim of this study was to characterize serum protein biomarkers for nutritional status that may be used as predictors for disease symptomatology in COVID-19 patients before and after vaccination. In pre-vaccine cohorts, proteomics analysis revealed significant differences between groups, with serum proteins alpha-1-acid glycoproteins (AGPs) 1 and 2, C-reactive protein (CRP) and retinol binding protein (RBP) increasing with COVID-19 severity, in contrast with serum albumin, transthyretin (TTR) and serotransferrin (TF) reduction as the symptomatology increased. Immunoassay reproduced and validated proteomics results of serum proteins albumin and RBP. In post-vaccine cohorts, the results showed the same pattern as in pre-vaccine cohorts for serum proteins AGPs, CRP, albumin and TTR. However, TF levels were similar between groups and RBP presented a slight reduction as COVID-19 symptomatology increased. In these cohorts, immunoassay validated proteomics results of serum proteins albumin, TTR and TF. Additionally, immune response to α-Gal in pre-vaccine cohorts varied in predominant immunoglobulin type profile, while post-vaccine groups presented mainly anti-α-Gal protective IgG antibodies. The study identified serum nutritional biomarkers that could potentially predict an accurate prognostic of COVID-19 disease to provide an appropriate nutritional care and guidance in non-vaccinated and vaccinated individuals against SARS-CoV-2. These results highlight the importance of designing personalized nutrition protocols to improve diet along with the application of prebiotics or probiotics for the control of COVID-19 and other infectious diseases.

Prognostic value of nutritional and inflammatory indicators in females with esophageal squamous cell cancer: A propensity score matching study

Background: Esophageal squamous cell cancer (ESCC) is a disease with a male predominance. Accordingly, the applicability of prognostic indicators values previously set for the general population with ESCC has not been reported for determining the physical state in females.

Methods: Patients with ESCC were pooled from 2009 to 2017 at Sichuan Cancer Hospital. We determined the differences in the nutritional and inflammatory indicators between gender by sex-stratified survival analysis in all cohorts (n = 2,660) and matching cohorts (n = 483 pairs) separately. Propensity score matching (PSM) was employed to eliminate selection bias between genders. We further performed the prognostic value of total cholesterol (TC) by subgroup analysis in the female cohort. The area ROC curve was used to assess the predictive performance of TC in females.

Results: There were a total of 2,660 patients with ESCC, of whom 2,173 (81.7%) were male and 487 (18.3%) were female. Before PSM, the prognostic nutritional index was an independent factor for OS in males but not in females. For cohort with or without matching, TC was an independent prognostic factor in females not for males. Furthermore, female patients with high TC level had significant poor OS in stages III and IV. The AUCs of TC were 0.63 and 0.70 for predicting 3- and 5-year OS, respectively.

Conclusion: Based on a much larger cohort, we confirmed that gender was a significant prognostic factor for ESCC patients. Interestingly, we found a significant difference in TC related to ESCC prognosis between genders. Collectively, TC might be an independent prognostic factor in females with ESCC.

Comparison of Serum, Plasma, and Liver Zinc Measurements by AAS, ICP-OES, and ICP-MS in Diverse Laboratory Settings

Progress improving zinc nutrition globally is slowed by limited understanding of population zinc status. This challenge is compounded when small differences in measurement can bias the determination of zinc deficiency rates. Our objective was to evaluate zinc analytical accuracy and precision among different instrument types and sample matrices using a standardized method. Participating laboratories analyzed zinc content of plasma, serum, liver samples, and controls, using a standardized method based on current practice. Instrument calibration and drift were evaluated using a zinc standard. Accuracy was evaluated by percent error vs. reference, and precision by coefficient of variation (CV). Seven laboratories in 4 countries running 9 instruments completed the exercise: 4 atomic absorbance spectrometers (AAS), 1 inductively coupled plasma optical emission spectrometer (ICP-OES), and 4 ICP mass spectrometers (ICP-MS). Calibration differed between individual instruments up to 18.9% (p < 0.001). Geometric mean (95% CI) percent error was 3.5% (2.3%, 5.2%) and CV was 2.1% (1.7%, 2.5%) overall. There were no significant differences in percent error or CV among instrument types (p = 0.91, p = 0.15, respectively). Among sample matrices, serum and plasma zinc measures had the highest CV: 4.8% (3.0%, 7.7%) and 3.9% (2.9%, 5.4%), respectively (p < 0.05). When using standardized materials and methods, similar zinc concentration values, accuracy, and precision were achieved using AAS, ICP-OES, or ICP-MS. However, method development is needed for improvement in serum and plasma zinc measurement precision. Differences in calibration among instruments demonstrate a need for harmonization among laboratories.

Relationship between Undernutrition and Periodontal Diseases among a Sample of Yemeni Population: A Cross-Sectional Study

Undernutrition is an inadequate supply of energy and nutrients. Periodontal diseases (PDs) are defined as a broad form of chronic inflammatory disease of the gingiva, bone, and ligaments supporting the teeth. This study aimed to reveal the relationship between undernutrition, using body mass index (BMI) and serum albumin level (Alb), and PDs in a sample of Yemeni population. A cross-sectional study was conducted at dental teaching clinics at the Faculty of Dentistry, Sana’a University. Of 1920 patients who attended clinics, only 229 matched the study criteria. Oral examination was performed to assess the periodontal clinical parameter measurements. BMI and Alb were measured. Participants of both genders were involved, with a slight increase in males (n = 134, 58.5%), and most of the study sample was in the age group of 18–35 years (n = 209, 91.3%). Regarding habits, only 18.2% (n = 43) of patients were smokers and about half of the participants (n = 136, 59.4%) were khat chewers. Most cases had mild undernutrition according to BMI (n = 139, 60.7%) and normal Alb level (n = 213, 93%). Regarding the periodontal diagnosis, most of the participants were diagnosed with gingivitis (n = 186, 81.2%). BMI and albumin level were nonsignificantly associated with PDs. PDs were statistically significant with the participant’s age, gender, level of education, and smoking ( $P>0.05$ ). However, BMI, khat chewing, and albumin level were nonsignificant factors of periodontal diseases among Yemeni participants ( $P>0.05$ ). In both genders, variables such as age of the patients, smoking, khat chewing, and PDs were nonsignificantly associated with BMI. This study showed that the majority of the participants had been diagnosed with gingivitis, but there was not an association between PDs and undernutrition. This paper is presented on research square URL // https://www.researchsquare.com/article/rs-429796/v1 with DOI 10.21203/rs.3.rs-429796/v1.

Dietary patterns related to zinc and polyunsaturated fatty acids intake are associated with serum linoleic/dihomo-γ-linolenic ratio in NHANES males and females

Identifying dietary patterns that contribute to zinc (Zn) and fatty acids intake and their biomarkers that may have an impact on health of males and females. The present study was designed to (a) extract dietary patterns with foods that explain the variation of Zn and PUFAs intake in adult men and women; and (b) evaluate the association between the extracted dietary patterns with circulating levels of serum dihomo-γ-linolenic fatty acid (DGLA) or serum linoleic/dihomo-γ-linolenic (LA/DGLA) ratio in males and females. We used reduced rank regression (RRR) to extract the dietary patterns separated by sex in the NHANES 2011-2012 data. A dietary pattern with foods rich in Zn (1st quintile = 8.67 mg/day; 5th quintile = 11.11 mg/day) and poor in PUFAs (5th quintile = 15.28 g/day; 1st quintile = 18.03 g/day) was found in females (S-FDP2) and the same pattern, with foods poor in PUFAs (5th quintile = 17.6 g/day; 1st quintile = 20.7 g/day) and rich in Zn (1st quintile = 10.4 mg/day; 5th quintile = 12.9 mg/day) (S-MDP2), was found in males. The dietary patterns with foods rich in Zn and poor in PUFAs were negatively associated with serum LA/DGLA ratio. This is the first study to associate the LA/DGLA ratio with Zn and PUFAs related dietary patterns in males and females.

Diet Quality: A Neglected Parameter in Children With Food Allergies. A Cross-Sectional Study

Background-Objective: With recent evidence suggesting that growth is no longer considered a major issue in children with food allergies (FA) on elimination diet, priority has shifted to diet quality to establish healthy eating patterns and prevent non-communicable diseases. The Diet Quality Index - International (DQI-I) could be useful for assessing the overall diet quality of FA-children. This study aimed to evaluate the impact of elimination diet on DQI-I in children with FA and the accuracy of DQI-I in reflecting nutrient intake. Materials-methods: In a prospective, cross-sectional, cohort study of FA-children (2-14 years), nutritional intake was evaluated using a 7-day food frequency questionnaire, 24-h dietary recall, and the DQI-I. Results: Of the 76 children recruited, 44.7% had multiple allergies. Mean overall DQI-I score was 52 points, with only 28% of participants having good overall DQI-I (≥60 points). DQI-I moderation and balance were the most affected domains. Participants with multiple allergies had higher DQI-I moderation and balance and lower vitamin D and Ca intake. Compared to toddlers, schoolchildren had higher DQI-I variety and lower moderation and received higher vitamin B2, vitamin B12, Ca, P, and Zn. The number of allergies, age, and milk avoidance were independently associated with adjusted DQI-I moderation and balance, energy, and certain micronutrient intake. Higher percentages of participants with good DQI-I received adequate amounts of Mn and vitamins A, B6, C, and folate than those with poor DQI-I. Conclusions: In children with FA on elimination diet, the DQI-I accurately captured the deflection of diet quality related to the development of chronic, non-communicable diseases through its moderation and balance components. This is DQI-I's main purpose as a healthy diet indicator and as such it would be a useful tool responding to the needs of the contemporary shifting of priorities in FA-children's diet from quantity to quality. Nevertheless, it does not accurately reflect the intake of certain micronutrients potentially compromised by elimination diets. Therefore, regular nutritional assessment utilizing both the DQI-I and tools assessing individual nutrient intakes along with professional nutrition counseling should be integral parts of the individualized management of children with FA to ensure adequate nutrient intake and establish healthy dietary patterns.

The association of dietary patterns with cognition through the lens of neuroimaging-a Systematic review

Despite the reported benefits of diet on cognition in older adults, randomized controlled trials (RCT) testing the impact of dietary interventions on cognitive scores have yielded less promising results when cognition was assessed via neuropsychological tests. More recently, neuroimaging has been used to identify more subtle brain-related changes associated to cognition. Hence, employing a combination of neuroimaging techniques with neuropsychological tests could clarify this controversy. To determine the effect of diet on cognitive performance, we conducted a systematic review of PubMed and Scopus databases for all studies, on middle-aged and older adults, combining neuroimaging, neuropsychological tests, and data on dietary patterns. The inclusion criteria were met by 14 observational studies and no RCTs. The range of brain measures assessed varied from volumes to white matter integrity, functional connectivity, brain glucose metabolism and beta-amyloid deposition. Given the variability of methods used in assessing cognitive performance, diet and brain correlates, conducting a meta-analysis was not possible. Here the evidence suggests that, in observational studies, dietary patterns may be associated with brain correlates that have been shown to precede cognitive decline. As such, neuroimaging should be included in future RCTs to identify any benefits of diet on brain measures linked with cognitive health.

Validity of a dish composition database for estimating protein, sodium and potassium intakes against 24 h urinary excretion: comparison with a standard food composition database

OBJECTIVE

We assessed the validity of a recently developed dish composition database (DCD) against urinary biomarkers compared with a standard food composition database (FCD).

DESIGN

Intakes of protein, Na and K were estimated by 2 × 24 h urine collections and by 4 d dietary record data based on the DCD (including 128 dishes) or FCD (including 1878 foods).

SETTING

Japan.

PARTICIPANTS

A total of 161 men and 163 women aged 20-69 years.

RESULTS

Compared with the 24 h urine-based estimates, the median intakes estimated using the DCD and FCD differed significantly for protein and Na in men and for Na and K in women. Deattenuated Spearman correlation coefficients using 24 h urine-based estimates for the intakes of protein, Na and K were lower in the DCD (respectively: 0·26, 0·15 and 0·44 in men; 0·22, 0·27 and 0·22 in women) than those in the FCD (respectively: 0·43, 0·40 and 0·59 in men; 0·33, 0·45 and 0·42 in women). When data on dish portion size reported by participants were used for estimation instead of standard portion-size data based on the DCD, the accuracy of the estimated median intakes did not change notably, whereas the deattenuated correlation coefficients improved (for protein, Na and K respectively: 0·32, 0·31 and 0·56 in men; 0·31, 0·41 and 0·39 in women).

CONCLUSIONS

The DCD supported by individual-level information on dish portion size showed fair to moderate validity in ranking individuals according to their intakes of protein, Na and K, similar to the FCD.

A Diet High in Processed Foods, Total Carbohydrates and Added Sugars, and Low in Vegetables and Protein Is Characteristic of Youth with Avoidant/Restrictive Food Intake Disorder

Avoidant/restrictive food intake disorder (ARFID) is characterized in part by limited dietary variety, but dietary characteristics of this disorder have not yet been systematically studied. Our objective was to examine dietary intake defined by diet variety, macronutrient intake, and micronutrient intake in children and adolescents with full or subthreshold ARFID in comparison to healthy controls. We collected and analyzed four-day food record data for 52 participants with full or subthreshold ARFID, and 52 healthy controls, aged 9-22 years. We examined frequency of commonly reported foods by logistic regression and intake by food groups, macronutrients, and micronutrients between groups with repeated-measures ANOVA. Participants with full or subthreshold ARFID did not report any fruit or vegetable category in their top five most commonly reported food categories, whereas these food groups occupied three of the top five groups for healthy controls. Vegetable and protein intake were significantly lower in full or subthreshold ARFID compared to healthy controls. Intakes of added sugars and total carbohydrates were significantly higher in full or subthreshold ARFID compared to healthy controls. Individuals with full or subthreshold ARFID had lower intake of vitamins K and B12, consistent with limited vegetable and protein intake compared to healthy controls. Our results support the need for diet diversification as part of therapeutic interventions for ARFID to reduce risk for nutrient insufficiencies and related complications.

Nutritional disorders resulting from food allergy in children

The elimination of food allergens that contribute essential nutrients in paediatrics may lead to the development of nutritional disorders. The most common nutritional disorders include poor growth, micronutrient deficiencies and feeding difficulties. Of the aforementioned, growth faltering has been well studied and is seen as a common presenting factor in paediatric food allergy. However, the use of different criteria and cut-off values makes it difficult to establish the overall effect. The impact of number and type of foods eliminated and comorbidities has yielded varying results, although there seems to be a trend towards worsening growth with atopic dermatitis and the avoidance of cow's milk. Low micronutrient intake is common in paediatric food allergy; however, a low intake does not necessarily translate into a deficiency as measured by biomarkers. Vitamin D and calcium have been well studied, and a long-lasting impact on bone mineral density has been found. However, other micronutrient deficiencies have also been found and should also be considered. Feeding difficulties is a common complaint in clinical practice, but limited data have been published in food allergy. Poor growth and reflux/vomiting have been shown to be associated with feeding difficulties, in particular in non-IgE-mediated food allergies. There seems to be a long-lasting effect on feeding, in particular in cow's milk allergy, which needs to be taken into account with dietary input. The interplay between growth, feeding difficulties and micronutrient deficiencies has been implied in some studies, but cause and effect is not well established and requires further research.

Variations in plasma choline and metabolite concentrations in healthy adults

BACKGROUND

Plasma concentrations of choline and its metabolites might serve as biomarkers for the health outcomes of several pathological states such as cardiovascular disease and cancer. However, information about the reliability of biomarkers of choline status is limited. We investigated biological variations in repeated measures of choline and metabolites in healthy adults to assess them as biomarkers.

METHODS

Blood samples were collected after an overnight fast at three-time points 12 days apart from 40 adults (mean age, 33 y; male, n = 21). A subset (n = 19; [male, n = 8]) provided one additional sample after a breakfast meal. Plasma free choline, betaine and dimethylglycine were measured using liquid chromatography-tandem mass spectrometry, and plasma phosphatidylcholine, sphingomyelin and lysophosphatidylcholine were measured using high-performance liquid chromatography.

RESULTS

The biological variations observed for choline and metabolites were ≤ 13% for adult fasting samples. This corresponded to intra-class correlations (ICC) that ranged from 0.593 to 0.770 for fasting values for choline and metabolites. A similar ICC range was also obtained between fasting and post-prandial states. Although most post-prandial concentrations of choline and metabolites were significantly higher (P < .05) than fasting, all fell within a calculated reference interval. The participants were correctly classified in tertiles for fasting and post-prandial states for choline (68%) and metabolites (range = 32% phosphatidylcholine and 79% for sphingomyelin).

CONCLUSIONS

These findings indicate that biological variations of choline and metabolites are low in healthy adults and values from a single blood sample can be used as a biomarker. However, choosing phosphatidylcholine as a biomarker is less reliable.

Validation of biomarkers of food intake-critical assessment of candidate biomarkers

Biomarkers of food intake (BFIs) are a promising tool for limiting misclassification in nutrition research where more subjective dietary assessment instruments are used. They may also be used to assess compliance to dietary guidelines or to a dietary intervention. Biomarkers therefore hold promise for direct and objective measurement of food intake. However, the number of comprehensively validated biomarkers of food intake is limited to just a few. Many new candidate biomarkers emerge from metabolic profiling studies and from advances in food chemistry. Furthermore, candidate food intake biomarkers may also be identified based on extensive literature reviews such as described in the guidelines for Biomarker of Food Intake Reviews (BFIRev). To systematically and critically assess the validity of candidate biomarkers of food intake, it is necessary to outline and streamline an optimal and reproducible validation process. A consensus-based procedure was used to provide and evaluate a set of the most important criteria for systematic validation of BFIs. As a result, a validation procedure was developed including eight criteria, plausibility, dose-response, time-response, robustness, reliability, stability, analytical performance, and inter-laboratory reproducibility. The validation has a dual purpose: (1) to estimate the current level of validation of candidate biomarkers of food intake based on an objective and systematic approach and (2) to pinpoint which additional studies are needed to provide full validation of each candidate biomarker of food intake. This position paper on biomarker of food intake validation outlines the second step of the BFIRev procedure but may also be used as such for validation of new candidate biomarkers identified, e.g., in food metabolomic studies.

An overview on the interplay between nutraceuticals and gut microbiota

Background

Nowadays, growing attention was being given to the alternative ways to prevent or treat diseases. Nutraceuticals are used increasingly for this purpose. Many of these are being used as alternative therapy. Classic therapy with synthetic drugs, although very effective, has many side effects. The term “nutraceuticals” refers to the link between the nutritional and pharmaceutical domains. Also, lately, many studies have been done to investigate the role of microbiota in maintaining health. There is the hypothesis that some of the health benefits of nutraceuticals are due to their ability to change the microbiota. The aim of this review was to emphasize the link between the most commonly used nutraceuticals, the microbiota and the health benefits.

Methods

We selected the articles in PubMed, published up to July 2017, that provided information about most used nutraceuticals, microbiota and health benefits. In this review, we incorporate evidence from various types of studies, including observational, in vitro and in vivo, clinical studies or animal experiments.

Results

The results demonstrate that many nutraceuticals change the composition of microbiota and can interfere with health status of the patients.

Discussion

There is evidence which sustains the importance of nutraceuticals in people’s health through microbiota but further studies are needed to complete the assessment of nutraceuticals in health benefit as a consequence of microbiota’s changing.

Evaluation of Blood Biomarkers Associated with Risk of Malnutrition in Older Adults: A Systematic Review and Meta-Analysis

Malnutrition is a common yet under-recognized problem in hospitalized patients. The aim of this paper was to systematically review and evaluate malnutrition biomarkers among order adults. Eligible studies were identified through Cochrane, PubMed and the ProQuest Dialog. A meta-regression was performed on concentrations of biomarkers according to malnutrition risks classified by validated nutrition assessment tools. A total of 111 studies were included, representing 52,911 participants (55% female, 72 ± 17 years old) from various clinical settings (hospital, community, care homes). The estimated BMI (p < 0.001) and concentrations of albumin (p < 0.001), hemoglobin (p < 0.001), total cholesterol (p < 0.001), prealbumin (p < 0.001) and total protein (p < 0.05) among subjects at high malnutrition risk by MNA were significantly lower than those without a risk. Similar results were observed for malnutrition identified by SGA and NRS-2002. A sensitivity analysis by including patients with acute illness showed that albumin and prealbumin concentrations were dramatically reduced, indicating that they must be carefully interpreted in acute care settings. This review showed that BMI, hemoglobin, and total cholesterol are useful biomarkers of malnutrition in older adults. The reference ranges and cut-offs may need to be updated to avoid underdiagnosis of malnutrition.

Use of biomarkers to assess fruit and vegetable intake

A high intake of fruit and vegetables (FV) has been associated with reduced risk of a number of chronic diseases, including CVD. The aim of this review is to describe the potential use of biomarkers to assess FV intake. Traditional methods of assessing FV intake have limitations, and this is likely to impact on observed associations with disease outcomes and markers of disease risk. Nutritional biomarkers may offer a more objective and reliable method of assessing dietary FV intake. Some single blood biomarkers, such as plasma vitamin C and serum carotenoids, are well established as indicators of FV intake. Combining potential biomarkers of intake may more accurately predict overall FV intake within intervention studies than the use of any single biomarker. Another promising approach is metabolomic analysis of biological fluids using untargeted approaches to identify potential new biomarkers of FV intake. Using biomarkers to measure FV intake may improve the accuracy of dietary assessment.

Challenges and Lessons Learned in Generating and Interpreting NHANES Nutritional Biomarker Data

For the past 45 y, the National Center for Health Statistics at the CDC has carried out nutrition surveillance of the US population by collecting anthropometric, dietary intake, and nutritional biomarker data, the latter being the focus of this publication. The earliest biomarker testing assessed iron and vitamin A status. With time, a broad spectrum of water- and fat-soluble vitamins was added and biomarkers for other types of nutrients (e.g., fatty acids) and bioactive dietary compounds (e.g., phytoestrogens) were included in NHANES. The cross-sectional survey is flexible in design, and biomarkers may be measured for a short period of time or rotated in and out of surveys depending on scientific needs. Maintaining high-quality laboratory measurements over extended periods of time such that trends in status can be reliably assessed is a major goal of the testing laboratories. Physicians, health scientists, and policy makers rely on the NHANES reference data to compare the nutritional status of population groups, to assess the impact of various interventions, and to explore associations between nutritional status and health promotion or disease prevention. Focusing on the continuous NHANES, which started in 1999, this review uses a "lessons learned" approach to present a series of challenges that are relevant to researchers measuring biomarkers in NHANES and beyond. Some of those challenges are the use of multiple related biomarkers instead of a single biomarker for a specific nutrient (e.g., folate, vitamin B-12, iron), adhering to special needs for specimen collection and handling to ensure optimum specimen quality (e.g., vitamin C, folate, homocysteine, iodine, polyunsaturated fatty acids), the retrospective use of long-term quality-control data to correct for assay shifts (e.g., vitamin D, vitamin B-12), and the proper planning for and interpretation of crossover studies to adjust for systematic method changes (e.g., folate, vitamin D, ferritin).

Precision nutrition - review of methods for point-of-care assessment of nutritional status

Precision nutrition encompasses prevention and treatment strategies for optimizing health that consider individual variability in diet, lifestyle, environment and genes by accurately determining an individual's nutritional status. This is particularly important as malnutrition now affects a third of the global population, with most of those affected or their care providers having limited means of determining their nutritional status. Similarly, program implementers often have no way of determining the impact or success of their interventions, thus hindering their scale-up. Exciting new developments in the area of point-of-care diagnostics promise to provide improved access to nutritional status assessment, as a first step towards enabling precision nutrition and tailored interventions at both the individual and community levels. In this review, we focus on the current advances in developing portable diagnostics for assessment of nutritional status at point-of-care, along with the numerous design challenges in this process and potential solutions.

Concepts and Controversies in Evaluating Vitamin K Status in Population-Based Studies

A better understanding of vitamin K's role in health and disease requires the assessment of vitamin K nutritional status in population and clinical studies. This is primarily accomplished using dietary questionnaires and/or biomarkers. Because food composition databases in the US are most complete for phylloquinone (vitamin K1, the primary form in Western diets), emphasis has been on phylloquinone intakes and associations with chronic diseases. There is growing interest in menaquinone (vitamin K2) intakes for which the food composition databases need to be expanded. Phylloquinone is commonly measured in circulation, has robust quality control schemes and changes in response to phylloquinone intake. Conversely, menaquinones are generally not detected in circulation unless large quantities are consumed. The undercarboxylated fractions of three vitamin K-dependent proteins are measurable in circulation, change in response to vitamin K supplementation and are modestly correlated. Since different vitamin K dependent proteins are implicated in different diseases the appropriate vitamin K-dependent protein biomarker depends on the outcome under study. In contrast to other nutrients, there is no single biomarker that is considered a gold-standard measure of vitamin K status. Most studies have limited volume of specimens. Strategic decisions, guided by the research question, need to be made when deciding on choice of biomarkers.

A Review of Cutoffs for Nutritional Biomarkers

The nutritional status of an individual or population needs to be assessed through valid and reliable biomarkers. Cutoffs generally have an underlying relation to health status and are one of the important quantitative criteria against which biomarker outputs are compared. For this reason, cutoffs are integral for surveys, surveillance, screening, interventions, monitoring, and evaluation. Despite their importance, nutritional biomarker cutoffs have not been adequately addressed in the literature. Furthermore, the field has not reached a consensus on which cutoff to use for each biomarker, and different cutoffs are often used for the same biomarkers in published studies. This review provides a comprehensive overview of cutoffs related to nutritional biomarkers and highlights some of the high-priority research gaps and challenges of using micronutrient case studies.

Prediction of fruit and vegetable intake from biomarkers using individual participant data of diet-controlled intervention studies

Fruit and vegetable consumption produces changes in several biomarkers in blood. The present study aimed to examine the dose–response curve between fruit and vegetable consumption and carotenoid (α-carotene, β-carotene, β-cryptoxanthin, lycopene, lutein and zeaxanthin), folate and vitamin C concentrations. Furthermore, a prediction model of fruit and vegetable intake based on these biomarkers and subject characteristics (i.e. age, sex, BMI and smoking status) was established. Data from twelve diet-controlled intervention studies were obtained to develop a prediction model for fruit and vegetable intake (including and excluding fruit and vegetable juices). The study population in the present individual participant data meta-analysis consisted of 526 men and women. Carotenoid, folate and vitamin C concentrations showed a positive relationship with fruit and vegetable intake. Measures of performance for the prediction model were calculated using cross-validation. For the prediction model of fruit, vegetable and juice intake, the root mean squared error (RMSE) was 258·0 g, the correlation between observed and predicted intake was 0·78 and the mean difference between observed and predicted intake was − 1·7 g (limits of agreement: − 466·3, 462·8 g). For the prediction of fruit and vegetable intake (excluding juices), the RMSE was 201·1 g, the correlation was 0·65 and the mean bias was 2·4 g (limits of agreement: − 368·2, 373·0 g). The prediction models which include the biomarkers and subject characteristics may be used to estimate average intake at the group level and to investigate the ranking of individuals with regard to their intake of fruit and vegetables when validating questionnaires that measure intake.

Urinary tartaric acid as a potential biomarker for the dietary assessment of moderate wine consumption: a randomised controlled trial

The availability of biomarkers that allow the estimation of the intake of specific foods and dietary components, as an alternative or addition to self-reported dietary questionnaires, could greatly enhance the effectiveness of nutritional research. The aim of the present study was to assess tartaric acid, one of the major components of red and white wines, as a potential biomarker of wine consumption. A total of twenty-one healthy men participated in a randomised cross-over feeding trial. They consumed a single dose of 100, 200 or 300 ml wine at dinner. Before each intervention, the participants followed a 7 d washout period during which they avoided consuming wine or grape-based products. Morning urine was collected and analysed by liquid chromatography coupled to electrospray ionisation tandem MS. A strong significant correlation was found between wine intake and urinary tartaric acid (r(s) = 0·9220; P <0·001). Using a cut-off value of 8·84 μg/mg creatinine, tartaric acid allowed wine consumers to be differentiated from non-wine consumers. The results suggest that urinary tartaric acid may be a sensitive and specific dietary biomarker of wine consumption.

Plasma-serum cholesterol differences in children and use of measurements from different specimens

BACKGROUND

We aimed to assess absolute plasma-serum differences and differences in ranking of total cholesterol (TC), high-density lipoprotein cholesterol (HDLC), and TC/HDLC ratio in children.

METHODS

We analysed data of 412 children participating in a Dutch birth cohort. TC, HDLC, and TC/HDLC ratio were determined in plasma at age 8 and 12 years and in serum at age 12 years.

RESULTS

Compared to serum, plasma TC at age 12 years was 0.07 mmol/l lower (95% CI -0.08 to -0.06), plasma HDLC was 0.06 mmol/l higher (95% CI 0.05-0.07), and plasma TC/HDLC ratio was 0.19 lower (95% CI -0.20 to -0.17) (p < 0.0001). Intraclass correlation coefficients (ICCs) for ranking of TC, HDLC, and TC/HDLC ratio at age 12 years were 0.970, 0.745, and 0.979, respectively. ICCs for ranking of 8- to 12-year change of TC, HDLC, and TC/HDLC ratio were 0.971, 0.957, and 0.955, respectively.

CONCLUSIONS

Cholesterol was systematically different in plasma and serum, and use of plasma would result in a more favourable lipid profile of children (lower TC, higher HDLC, and lower TC/HDLC ratio). Nevertheless, consistency in ranking of children according to plasma or serum cholesterol concentrations was very high. Age-related change in cholesterol can be validly assessed by ranking the difference between serum concentrations at one age and plasma concentrations at another age.

Markers for nutrition studies: review of criteria for the evaluation of markers

INTRODUCTION

Markers are important tools to assess the nutrition status and effects of nutrition interventions. There is currently insufficient consensus in nutrition sciences on how to evaluate markers, despite the need for properly evaluating them.

OBJECTIVES

To identify the criteria for the evaluation of markers related to nutrition, health and disease and to propose generic criteria for evaluation.

METHOD

The report on "Evaluation of Biomarker and Surrogate Endpoints in Chronic Disease" from the Institute of Medicine was the starting point for the literature search. Additionally, specific search strategies were developed for Pubmed.

RESULTS

In nutrition, no set of criteria or systematic approach to evaluate markers is currently available. There is a reliance on the medical area where statistical methods have been developed to quantify the evaluation of markers. Even here, a systematic approach is lacking-markers are still evaluated on a case-by-case basis. The review of publications from the literature search resulted in a database with definitions, criteria for validity and the rationale behind the criteria. It was recognized that, in nutrition, a number of methodological aspects differ from medical research.

CONCLUSIONS

The following criteria were identified as essential elements in the evaluation of markers: (1) the marker has a causal biological link with the endpoint, (2) there is a significant association between marker and endpoint in the target population, (3) marker changes consistently with the endpoint, e.g., in response to an intervention, and (4) change in the marker explains a substantial proportion of the change in the endpoint in response to the intervention.

Selected physiologic variables are weakly to moderately associated with 29 biomarkers of diet and nutrition, NHANES 2003-2006

The physiologic status of an individual may influence biomarkers of nutritional status. To help researchers with planning studies and interpreting data, we assessed the associations between common physiologic variables (fasting, inflammation, renal function, and pregnancy) and 29 biomarkers of diet and nutrition measured in blood or urine in a representative sample of the adult U.S. population (aged ≥ 20 y; pregnancy variable and iron indicators limited to women aged 20-49 y) participating in NHANES 2003-2006. We compared simple linear regression (model 1) with multiple linear regression [model 2, controlling for age, sex, race-ethnicity, smoking, supplement use, and the physiologic factors (and urine creatinine for urine biomarkers)] and report significant findings from model 2. Not being fasted was positively associated with most water-soluble vitamins (WSVs) and related metabolites (RMs). Some WSV, fat-soluble vitamin (FSV) and micronutrient (MN), and phytoestrogen concentrations were lower in the presence of inflammation (C-reactive protein ≥ 5 mg/L), whereas fatty acids and most iron indicators were higher. Most WSVs and RMs were higher when renal function was impaired [estimated glomerular filtration rate <60 mL/(min · 1.73 m(2))]. Most WSV, FSV and MN, and fatty acid concentrations were higher in pregnant compared with nonpregnant women, but vitamins A and B-12 and most iron indicators were lower. The estimated changes in biomarker concentrations with different physiologic status were mostly small to moderate (≤ 25%) and generally similar between models; renal function, however, showed several large differences for WSV and RM concentrations. This descriptive analysis of associations between physiologic variables and a large number of nutritional biomarkers showed that controlling for demographic variables, smoking, and supplement use generally did not change the interpretation of bivariate results. The analysis serves as a useful basis for more complex future research.

A conditional likelihood approach for regression analysis using biomarkers measured with batch-specific error

Measurement error is common in epidemiological and biomedical studies. When biomarkers are measured in batches or groups, measurement error is potentially correlated within each batch or group. In regression analysis, most existing methods are not applicable in the presence of batch-specific measurement error in predictors. We propose a robust conditional likelihood approach to account for batch-specific error in predictors when batch effect is additive and the predominant source of error, which requires no assumptions on the distribution of measurement error. Although a regression model with batch as a categorical covariable yields the same parameter estimates as the proposed conditional likelihood approach for linear regression, this result does not hold in general for all generalized linear models, in particular, logistic regression. Our simulation studies show that the conditional likelihood approach achieves better finite sample performance than the regression calibration approach or a naive approach without adjustment for measurement error. In the case of logistic regression, our proposed approach is shown to also outperform the regression approach with batch as a categorical covariate. In addition, we also examine a 'hybrid' approach combining the conditional likelihood method and the regression calibration method, which is shown in simulations to achieve good performance in the presence of both batch-specific and measurement-specific errors. We illustrate our method by using data from a colorectal adenoma study.

Robust statistical methods for analysis of biomarkers measured with batch/experiment-specific errors

In many biological studies, biomarkers are measured with errors. In addition, study samples are often divided and measured in separate batches, and data collected from different experiments are used in a single analysis. Generally speaking, the structure of the measurement error is unknown and is not easy to ascertain. While the conditions under which the measurements are taken vary from one batch/experiment to another, they are often held steady within each batch/experiment. Thus, the measurement error can be considered batch/experiment specific, that is, fixed within each batch/experiment, which results into a rank-preserving property within each batch/experiment. Under this condition, we study robust statistical methods for analyzing the association between an outcome variable and predictors measured with error, and evaluating the diagnostic or predictive accuracy of these biomarkers. Our methods require no assumptions on the structure and distribution of the measurement error, which are often unrealistic. Compared with existing methods that are predicated on normality and additive structure of measurement errors, our methods still yield valid inferences under departure from these assumptions. The proposed methods are easy to implement using off-shelf software. Simulation studies show that under various measurement error structures, the performance of the proposed methods is satisfactory even for a fairly small sample size, whereas existing methods under misspecified structures and a naive approach exhibited substantial bias. Our methods are illustrated using a biomarker validation case-control study for colorectal neoplasms.

Performance characteristics of plasma amyloid-beta 40 and 42 assays

Identifying biomarkers of Alzheimer's disease (AD) risk will be critical to effective AD prevention. Levels of circulating amyloid-beta (Abeta) 40 and 42 may be candidate biomarkers. However, properties of plasma Abeta assays must be established. Using five different protocols, blinded samples were used to assess: intra-assay reproducibility; impact of EDTA vs. heparin anticoagulant tubes; and effect of time-to-blood processing. In addition, percent recovery of known Abeta concentrations in spiked samples was assessed. Median intra-assay coefficients of variation for the assay protocols ranged from 6-24% for Abeta(40), and 8-14% for Abeta(42). There were no systematic differences in reproducibility by collection method. Plasma concentrations of Abeta (particularly Abeta(42) appeared stable in whole blood kept in ice packs and processed as long as 24 hours after collection. Recovery of expected concentrations was modest, ranging from -24% to 44% recovery of Abeta(40), and 17% to 61% of Abeta(42). In conclusion, across five protocols, plasma Abeta(40) and Abeta(42) levels were measured with generally low error, and measurements appeared similar in blood collected in EDTA versus heparin. While these preliminary findings suggest that measuring plasma Abeta(40) and Abeta(42) may be feasible in varied research settings, additional work in this area is necessary.

A new FFQ designed to measure the intake of fatty acids and antioxidants in children

Objective

The present paper describes the systematic development of an FFQ to assess the intake of fatty acids and antioxidants in school-aged children. In addition, a validation study applying 24 h dietary recalls was performed.

Design

Using the variance-based Max_r method, a list of eighty-two foods was compiled from data obtained by 3 d weighed dietary records. The foods were used to design an FFQ, the comprehensibility of which was evaluated in a feasibility study. In addition, the FFQ was validated in a subset of 101 children from the German Infant Nutritional Intervention Study (GINI PLUS) against one 24 h dietary recall.

Results

The feasibility study attested a good acceptance of the FFQ. Mean intake of foods compared well between the FFQ and the 24 h dietary recall, although intake data generated from the FFQ tended to be higher. This difference became less apparent at the nutrient level, although the estimated average consumption of arachidonic acid and EPA using the FFQ still exceeded values recorded with the 24 h recall method by 45 % and 29 %, respectively.

Conclusions

On the basis of the systematic selection process of the food list, the established practicability of the FFQ and the overall plausibility of the results, the use of this FFQ is justified in future epidemiological studies.

Opportunities and challenges in conducting systematic reviews to support the development of nutrient reference values: vitamin A as an example

Nutrient reference values have significant public health and policy implications. Given the importance of defining reliable nutrient reference values, there is a need for an explicit, objective, and transparent process to set these values. The Tufts Medical Center Evidence-based Practice Center assembled a group of nutrition experts from academic institutions and federal government agencies, led participants in discussions, conducted exercises in formulating questions and evidence review criteria that would be amenable to systematic reviews of the scientific literature, performed a literature search on the questions to identify potentially relevant publications, and identified challenges and limitations of applying this method to support the development of nutrient reference values using vitamin A as an example. The workgroup concluded that the systematic review approach could be productively used to inform the development of reference values. Challenges identified in this exercise include prioritizing and defining research questions when the volume of literature is large, relying on intermediate (surrogate) outcomes when few or no studies directly linking nutrient intake with clinical outcomes are available, and determining reliable nutrient biomarkers. Ultimately, an objective, unbiased systematic review of a defined question could be useful, not only in helping to set nutrient reference values, but also for increasing the transparency of the decision making process.

Omega-6 and trans fatty acids in blood cell membranes: a risk factor for acute coronary syndromes?

BACKGROUND

Although fatty acid intake has been associated with risk of coronary disease events, the association between blood omega-6 and trans fatty acids (FAs) at the time of an acute coronary syndrome (ACS) is unknown.

METHODS

The relationship of blood FA composition to ACS was analyzed in 768 incident cases and 768 controls (matched on age, sex, and race).

RESULTS

Compared to controls, ACS cases' blood cell membrane content of linoleic acid was 13% lower (P < .0001); arachidonic acid was 3.6% higher (P < .001); the trans isomer of oleic acid was 13.3% higher (P < .0001); and the trans-trans isomer of linoleic acid was 13.3% higher (P = .003). In multivariable analyses, a 1-SD decrease in linoleic acid was associated with >3 times the odds for being a case (odds ratio [OR] 3.23, 95% confidence interval [CI] 2.63-4.17). The relationship of arachidonic acid to ACS was U shaped; compared to the first quartile of arachidonic acid, the ORs for case status in the second, third, and fourth quartiles were 0.73 (95% CI 0.47-1.13), 0.65 (95% CI 0.41-1.04), and 2.32 (95% CI 1.39-3.90), respectively. The OR for a 1-SD increase in trans oleic acid was 1.24 (95% CI 1.06-1.45), and for trans-trans linoleic acid, 1.1 (95% CI 0.93-1.30). All associations were independent of membrane omega-3 FA content.

CONCLUSIONS

High blood levels of linoleic acid but low levels of trans oleic acid are inversely associated with ACS. The relationship of arachidonic acid to ACS appears more complex.

Ethnic and socioeconomic differences in variability in nutritional biomarkers

BACKGROUND

Several studies have reported ethnic, education, and income differentials in concentrations of selected nutritional biomarkers in the US population. Although biomarker measurements are not subject to biased self-reports, biologic variability due to individual characteristics and behaviors related to dietary exposures contributes to within-subject variability and measurement error.

OBJECTIVE

We aimed to establish whether the magnitude of components of variance for nutritional biomarkers also differs in these high-risk groups.

DESIGN

We used data from 2 replicate measurements of serum concentrations of vitamins A, C, D, and E; folate; carotenoids; ferritin; and selenium in the third National Health and Nutrition Examination Survey second examination subsample (n = 948) to examine the within-subject and between-subject components of variance. We used multivariate regression methods with log-transformed analyte concentrations as outcomes to estimate the ratios of the within-subject to between-subject components of variance by categories of ethnicity, income, and education.

RESULTS

In non-Hispanic blacks, the within-subject to between-subject variance ratio for beta-cryptoxanthin concentration was higher (0.23; 95% CI: 0.17, 0.29) relative to non-Hispanic whites (0.13; 0.11, 0.16) and Mexican Americans (0.11; 0.07, 0.14), and the lutein + zeaxanthin ratio was higher (0.29; 0.21, 0.38) relative to Mexican Americans (0.15; 0.10, 0.19). Higher income was associated with larger within-subject to between-subject variance ratios for serum vitamin C and red blood cell folate concentrations but smaller ratios for serum vitamin A. Overall, there were few consistent up- or down-trends in the direction of covariate-adjusted variability by ethnicity, income, or education.

CONCLUSION

Population groups at high risk of adverse nutritional profiles did not have larger variance ratios for most of the examined biomarkers.

Biological variability dominates and influences analytical variance in HPLC-ECD studies of the human plasma metabolome

Background

Biomarker-based assessments of biological samples are widespread in clinical, pre-clinical, and epidemiological investigations. We previously developed serum metabolomic profiles assessed by HPLC-separations coupled with coulometric array detection that can accurately identify ad libitum fed and caloric-restricted rats. These profiles are being adapted for human epidemiology studies, given the importance of energy balance in human disease.

Methods

Human plasma samples were biochemically analyzed using HPLC separations coupled with coulometric electrode array detection.

Results

We identified these markers/metabolites in human plasma, and then used them to determine which human samples represent blinded duplicates with 100% accuracy (N = 30 of 30). At least 47 of 61 metabolites tested were sufficiently stable for use even after 48 hours of exposure to shipping conditions. Stability of some metabolites differed between individuals (N = 10 at 0, 24, and 48 hours), suggesting the influence of some biological factors on parameters normally considered as analytical.

Conclusion

Overall analytical precision (mean median CV, ~9%) and total between-person variation (median CV, ~50–70%) appear well suited to enable use of metabolomics markers in human clinical trials and epidemiological studies, including studies of the effect of caloric intake and balance on long-term cancer risk.

Ethnicity is an independent correlate of biomarkers of micronutrient intake and status in American adults

Diet may be among the factors that mediate the acknowledged ethnicity and socioeconomic differentials in health. Biomarkers of nutritional exposure avoid reliance on biased self-reports of diet and allow an objective assessment of dietary differentials associated with ethnicity and socioeconomic position. We used data from the NHANES III (n = 13113) and NHANES 1999-2002 (n = 7246) to examine ethnic, education, and income differentials in serum concentrations of nutrients of putative public health importance (vitamins C, D, and E, folate, carotenoids, selenium, and ferritin) in U.S. adults. Multiple regression methods were used to adjust for covariates and complex survey design to examine these associations. The serum beta-cryptoxanthin and lutein + zeaxanthin concentrations, adjusted for education and income, were higher in nonwhites (P < 0.0001) relative to non-Hispanic whites. Non-Hispanic blacks had lower serum vitamins C and D, folate, and selenium concentrations relative to non-Hispanic-whites. The biomarker profile (except vitamin D, and folate and ferritin in women) of Mexican-Americans was comparable or better relative to non-Hispanic-whites. Ethnicity associations with mean biomarker concentrations generally paralleled these associations with the proportion of the population at risk of marginal concentrations. Education was an independent positive predictor of serum concentrations of several carotenoids and vitamin C (P Collapse

Key Words Collapse

MESH Headings

• Adult
• Biomarkers/blood
• Black People
• Ethnicity
• Health Surveys
• Humans
• Mexican Americans
• Micronutrients/blood
• Nutritional Status
• Regression Analysis
• Socioeconomic Factors
• United States
• Black or African American

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Grants

• CA108274 NCI NIH HHS
• Intramural NIH HHS

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Affiliation(s)

Ashima K Kant Department of Family, Nutrition, and Exercise Sciences, Queens College of the City University of New York, Flushing, NY 11367, USA.
Barry I Graubard

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Grenzen und Bedeutung der Labordiagnostik bei Mangelernährung im Alter

Despite the widespread interest in malnutrition in the elderly, the utility of laboratory tests is limited. This is because their diagnostic significance can be impaired by undercurrent diseases, pre-analytical effects and unsatisfactory standardization. This survey summarizes the most important parameters of malnutrition. Thus, "nitrogen balance" is considered the golden standard of nutrition status, while the diagnostic significance of serum proteins depends on their biological half-time. Albumin is seen as the most reliable malnutrition marker, but cholinesterase and cholesterol-decrease must also be mentioned. The so-called "low-T3-phenomenon" which is caused by the production of "reverse T3", seems to be the unique parameter for the "catabolic" state of metabolism. Of special interest are also prognostic markers of mortality, such as orosomucoid. Cytokines, other signal peptides, trace elements and vitamins are from the diagnostic point of view of rather limited significance. In sum, the diagnosis and monitoring of malnutrition in the elderly represents an important challenge for laboratory medicine.

Mapping the Theories of Preeclampsia: The Role of Homocysteine

OBJECTIVE

We conducted a systematic review to examine the hypothesized mechanism through which homocysteine could lead to preeclampsia.

DATA SOURCES

We searched MEDLINE, EMBASE, BIOSIS, SciSearch, and bibliographies of primary and review articles, and we contacted experts.

METHODS OF STUDY SELECTION

Of the 25 relevant primary articles, 8 studies measured total serum homocysteine concentrations before the clinical onset of preeclampsia (1,876 women), whereas 17 measured it afterward (1,773 women). Meta-analytic techniques were used to examine consistency, strength, temporality, dose-response, and plausibility of the disease mechanisms implicating folate, vitamin B(6), vitamin B(12), genetic polymorphisms, oxidative stress, and endothelial dysfunction in the pathway linking hyperhomocysteinemia to preeclampsia.

TABULATION, INTEGRATION, AND RESULTS

Overall, there were higher serum homocysteine concentrations among pregnant women with preeclampsia than among those with uncomplicated pregnancies, but the results were heterogeneous (P = .12; I(2) = 38.8%). Among studies with temporality, the size of association was smaller than that among those without (weighted mean difference 0.68 mumol/L versus 3.36 mumol/L; P < .006). There was no dose-response relationship between homocysteine concentration and severity of preeclampsia. The mechanisms underlying hyperhomocysteinemia (folate and vitamin B(12) deficiency and genetic polymorphisms) were not found to be plausible, but markers of oxidative stress and endothelial dysfunction were higher in hyperhomocysteinemia.

CONCLUSION

Homocysteine concentrations are slightly increased in normotensive pregnancies that later develop preeclampsia and are considerably increased once preeclampsia is established. However, because of a lack of consistency in data, dose-response relationship, and biologic plausibility, the observed association cannot be considered causal from the current literature.

Estimating laboratory precision of urinary albumin excretion and other urinary measures in the International Study on Macronutrients and Blood Pressure

Microalbuminuria is a risk factor for renal failure, stroke, and cardiovascular disease. However, estimating laboratory precision for albumin excretion is problematic because of its highly skewed distribution and the presence of values below assay detection limits. The authors used 781 quality control pairs from 24-hour urine samples collected between 1996 and 1999 in the International Study on Macronutrients and Blood Pressure (INTERMAP) to compare percentage of technical error (%TE), the usual estimate of laboratory precision, with the mean and median values of within-pair coefficients of variation (CVs) for urinary albumin concentration and other urinary variables. In INTERMAP, %TE was larger than mean CV for all variables. Exclusion of potentially mislabeled samples reduced this difference; for example, for sodium, estimates of %TE and mean and median CV were 2.37%, 0.75%, and 0.28%, respectively, for all 781 pairs and 0.84%, 0.48%, and 0.27%, respectively, with possibly mislabeled pairs excluded. For urinary albumin concentration, exclusion of one mislabeled pair changed estimates for %TE and mean CV from 29.6% and 20.8% to 20.6% and 20.6%, while median CV was unchanged at 9.4%. After exclusion of urinary albumin concentration pairs with values below the detection limit, estimates were 15.4%, 11.4%, and 6.4%, respectively. Results indicate that mean and median CV are not equivalent to %TE and that values below the detection limit can markedly affect estimates and should be excluded.

Antioxidant nutrients and chronic disease: use of biomarkers of exposure and oxidative stress status in epidemiologic research

Oxidation of lipid, nucleic acids or protein has been suggested to be involved in the etiology of several chronic diseases including cancer, cardiovascular disease, cataract, age-related macular degeneration and aging in general. A large body of research has investigated the potential role of antioxidant nutrients in the prevention of these and other chronic diseases. This review concentrates on the following antioxidant nutrients: beta-carotene and other carotenoids, vitamin E, vitamin C and selenium. The first part of the review emphasizes the utility of biological markers of exposure for these nutrients and the relationship to dietary intake data. The second part considers functional assays of oxidative stress status in humans including the strengths and limitations of various assays available for use in epidemiologic research. A wide variety of functional assays both in vivo and ex vivo, are covered, including various measures of lipid oxidation (thiobarbituric acid reactive substances, exhaled pentane/ethane, low-density lipoprotein resistance to oxidation, isoprostanes), DNA oxidation (oxidized DNA bases such as 8-OHdG, autoantibodies to oxidized DNA, modified Comet assay) and protein oxidation (protein carbonyls). Studies that have examined the effects of antioxidant nutrients on these functional markers are included for illustrative purposes. The review concludes with a discussion of methodologic issues and challenges for studies involving biomarkers of exposure to antioxidant nutrients and of oxidative stress status.

Methodologic and statistical considerations regarding use of biomarkers of nutritional exposure in epidemiology

In nutritional epidemiology, accurate quantification of nutritional exposure is critical. Even moderate flaws in measurement can lead to sizeable distortions in estimations of the effects of exposure. In many situations, this will lead to inaccurate direct estimation of exposure effects. In others, it will make it difficult to control for the confounding effects of nutritional exposure. Biomarkers offer important opportunities to advance research in nutritional epidemiology; their objectivity and potentially greater accuracy give them the potential to substantially lessen distortions that might result from imperfect measurements. Clearly, the accuracy of biomarkers as indicators of nutritional exposure is critical to their value. It is likely that establishing the accuracy of biomarkers will require some reference to self-reports, even if those reports are not as accurate as the biomarkers they are used to test. The goal of this paper is to describe aspects of accuracy-reproducibility, reliability and validity-as they apply to biomarkers in nutritional epidemiology.