13: Biomarkers (Chapter 15)
- Page ID
- 117024
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Nutritional biomarkers are defined as biological characteristics that can be objectively measured and evaluated as indicators of normal biological or pathogenic processes, or as responses to nutrition interventions. They can be classified as: (i) biomarkers of exposure; (ii) biomarkers of status; and (iii) biomarkers of function. Biomarkers of exposure are intended to measure intakes of foods or nutrients using traditional dietary assessment methods or objective dietary biomarkers. Status biomarkers measure a nutrient in biological fluids or tissues, or in the urinary excretion of a nutrient or its metabolites; these ideally reflect total body nutrient content or the status of the tissue store most sensitive to nutrient depletion. Functional biomarkers, subdivided into biochemical and physiological or behavioral biomarkers, assess the functional consequences of a nutrient deficiency or excess. They may measure the activity of a nutrient-dependent enzyme or the presence of abnormal metabolic products in urine or blood arising from reduced activity of the enzyme; these serve as early biomarkers of subclinical deficiencies. Alterations in DNA damage, in gene expression and in immune function are also emerging as promising functional biochemical biomarkers. Disturbances in functional physiological and behavioral biomarkers can occur with more severe nutrient deficiencies, often involving impairments in growth, vision, motor development, cognition, in response to vaccination, and the onset of, or an increase in, depression. Such functional biomarkers, however, lack both sensitivity and specificity as they are often also affected by social and environmental factors. Outlined here are the principles and procedures that influence the choice of the three classes of biomarkers, as well as confounding factors that may affect their interpretation. A brief review of biomarkers based on new technologies such as metabolomics, etc., is also provided. Methods for evaluating biomarkers at the population and individual level are also presented.
- 13.1: Biomarkers to assess nutritional status (15.1)
- This page discusses the importance of nutritional biomarkers for clinical guidance on health and nutrition, categorizing them into exposure, status, and function. It emphasizes the complexities in interpreting these biomarkers due to confounding factors. Strategies to enhance accuracy include standardized collection methods, demographic classification, and adjusting for inflammation effects.
- 13.2: Biomarkers of exposure (15.2)
- This page discusses the assessment of nutrient exposure biomarkers through various dietary methods, including 24-hour recalls and food records, each with their own strengths and limitations. It highlights the importance of considering factors such as dietary supplements and seasonality. Dietary biomarkers are classified into recovery, concentration, and predictive types, which help in evaluating dietary intake.
- 13.3: Biomarkers of status (15.3)
- This page covers various methods of assessing nutrient status through biomarkers derived from biological fluids and tissues, emphasizing the complexity and technical challenges of sample collection and analysis. Blood, urine, saliva, hair, and nails are discussed, each with unique benefits and limitations, such as contamination risks and variability in results. Techniques like ICP-MS and careful sample handling are crucial for accurate measurements.
- 13.4: Biomarkers of function (15.4)
- This page summarizes various functional biomarkers used to assess nutrient deficiencies, including biochemical and physiological types. Key indicators like methylmalonic acid for vitamin B12 and enzyme activity tests for other vitamins are highlighted. Techniques such as load tests and RDR evaluate nutrient status. The assessment of cognitive function and motor development related to nutrient deficiencies is discussed, with mixed evidence on the impact of supplementation.
- 13.5: Factors affecting choice of nutritional biomarkers (15.5)
- This page outlines the importance of carefully selecting nutritional biomarkers, taking into account biological factors and health conditions that may affect their accuracy and reliability. It discusses how diseases can alter nutrient levels, emphasizing the need for precise measurements and quality control in laboratory testing.
- 13.6: Evaluation of the selected nutritional biomarker (15.6)
- This page discusses the role of nutritional biomarkers in assessing health status and identifying deficiencies or excesses in populations. It highlights the importance of reference distributions, cutoff points, and the challenges of misclassification and variability. The need for repeated measurements and combining multiple biomarkers is emphasized to improve diagnostic accuracy.
- 13.7: Application of new technologies (15.7)
- This page explores the evolution of nutritional assessment methods, moving from traditional biomarkers to advanced "omics" technologies, including nutrigenetics, proteomics, and metabolomics. These approaches assess nutrient interactions, genetic influences on health, and metabolic states. Metabolomics specifically employs both targeted and non-targeted strategies in dietary intervention, disease studies, and biomarker identification, though results may vary.