Nutrition: obtaining reliable biomarker data to study the health status of populations

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1 Nutrition: obtaining reliable biomarker data to study the health status of populations Christine M. Pfeiffer, Ph.D. Chief, Nutritional Biomarkers Branch, DLS AAAS 2011 Annual Meeting Science Without Borders Session February 18, 2011 National Center for Environmental Health Division of Laboratory Sciences

2 Outline Introduction to CDC s Nutritional Biomarkers Branch Introduction to an important U.S. health survey, NHANES Vitamin D as an example: Evolution of measurement techniques used for NHANES Consequences of method changes on long-term monitoring of population trends Programs & partnerships across different sectors to improve measurements, make them comparable across the globe, and create a lasting impact on public health 2

3 CDC s Nutritional Biomarkers Branch WATER-SOLUBLE VITAMINS & METABOLITES Folate Vitamin B6 Vitamin B12 Vitamin i C Homocysteine Methylmalonic acid Iron-status indicators FAT-SOLUBLE VITAMINS & NUTRIENTS Vitamin A Vitamin E Carotenoids Vitamin D Polyunsaturated fatty acids DIETARY BIOACTIVE COMPOUNDS Phytoestrogens Caffeine and metabolites Polyphenols GOAL: Improve the laboratory diagnosis and detection of nutrition-related diseases 3

4 U.S. NHANES Cross-sectional nationally representative survey Conducted by the National Center for Health Statistics, CDC Designed to collect information about the health and diet of people in the United Statest Approximately 5,000 persons examined per year Unique in that t it combines a home interview with health tests that are done in a Mobile Examination Center 4

5 U.S. NHANES Sampling Design Stage 1 Counties Stage 2 Segments Stage 3 Households Stage 4 SPs 5

6 National Report on Biochemical Indicators of Diet and Nutrition in the U. S. Population

7 Reference Interval Tables by Age and Sex 7

8 Vitamin D Example Why is it important to measure biological levels of vitamin D? What measurement techniques are suitable for NHANES? What happens if measurement techniques have to be changed mid-stream? How do we make measurements comparable across the globe? What do we need to ensure high quality measurements? 8

9 9 Vitamin D: Nutrient of the Day

10 What is Vitamin D? Fat-soluble vitamin that helps the body absorb calcium Primarily needed for bone growth and bone remodeling Other roles in human heath Modulates neuromuscular and immune function Reduces inflammation 10

11 Main Sources of Vitamin D Sunlight: UVB exposure Vitamin D3 cholecalciferol Food Vitamin D3 cholecalciferol, animal sources Vitamin D2 ergocalciferol, plants (mushrooms) Supplements Vitamin D2 and vitamin D3 CDC. MMWR Recomm Rep 1992 Sep 11;41(RR-14):1-7 11

12 Vitamin D Metabolism Vitamin D is rapidly taken up and transported to the liver Vitamin D2 and vitamin D3 are metabolized o o First, in the liver to the circulating form of 25-hydroxyvitamin D or 25(OH)D Then in the kidney to the active form of 1,25-dihydroxyvitamin D CDC. MMWR Recomm Rep 1992 Sep 11;41(RR-14):1-7 12

13 Vitamin D and Health In children, there is a high risk of rickets with low levels of 25(OH)D In adults, there is a risk of osteomalacia with inadequate levels of 25(OH)D Low levels of 25(OH)D have been associated with increased risk for numerous other health outcomes These associations are primarily based on ecologic/observational studies 13

14 Why is it Important to Measure Biological Levels of Vitamin D? Because the level of serum 25(OH)D is the result of the cumulative exposure to various sources of vitamin D, it is considered to be the best biomarker to assess vitamin status. 14

15 What Measurement Techniques are Suitable for NHANES? Highest possible accuracy Best possible precision Good sensitivity because only small sample volumes are available High enough throughput to handle minimum 5,000 samples per year Stable over time to avoid method fluctuations Has to be affordable and sustainable over multiple years anes 15

16 History of Measurement of 25(OH) D in NHANES Radioimmunoassay (RIA) developed in the mid-1980s this was state-of-the-art at the time o o NHANES III ( ): Original DiaSorin RIA NHANES : Reformulated DiaSorin RIA Liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) this is state-of-the-art now o NHANES 2007 and forward anes 16

17 Undesirable Features of the Classical Immunoassay Methodology Suboptimal performance characteristics Specificity Precision Robustness Definition Compounds other than 25(OH)D may alter results Greater variation in laboratory measurements Fluctuations in assay performance over time Impact on population monitoring Difficult to obtain accurate testing results Difficult to identify small changes in the population over time Difficult to interpret changes in the population over time 17

18 Advantages of the New Analytical Methodology Isotope Dilution LC-MS/MS Separation of 25(OH)D 3 from epimer of 25(OH)D 3 (NIST SRM 972 Level 4) C:\Xcalibur\...\data090720a18 7/20/2009 4:50:35 PM SRM 972 L4 RT: SM: 5G NL: 1.32E6 Mass transition m/z: 401/383 TIC F: + p sid=-7.00 SRM ms @ [ ] ] MS data090720a18 Intensity (OH)D 3 epi-25(oh)d Time (min) RT: SM: 5G Intensity NL: 1.86E5 TIC F: + p sid=-7.00 SRM ms @ [ ] MS data090720a18 Mass transition 25(OH)D (m/z): 413/ Time (min)

19 Advantages of the New Analytical Methodology Isotope Dilution LC-MS/MS Specificity Precision Robustness Less possibility for compounds other than 25(OH)D to alter results <8% day-to-day variation In-house calibration with 25(OH)D 2 and 25(OH)D 3, and calibration verification with NIST reference material 19

20 How to Make Past and Current Data Comparable? In 2009, the NIH Office of Dietary Supplements and the CDC NCHS sponsored a roundtable on vitamin D issues in NHANES Future methodology should be LC-MS/MS A subset of the samples analyzed with the DiaSorin RIA will be re- analyzed by LC-MS/MS to bridge the past and the future Yetley EA et al. J. Nutr. Nov

21 Bridge to the Past will be Imperfect due to the Suboptimal Specificity of the Immunoassay Data 80% Difference Plot LC-MS/MS RIA - LC-MS/MS) / (DiaSorin 60% 40% 20% 0% -20% -40% Identity Bias (-9.7%) 95% CI 95% Limits of agreement (-44.0% to 24.5%) 95% CI -60% -80% LC-MS/MS (nmol/l) 21

22 Comparison of Data across Several Labs or Countries is Very Resource-Intensive Canada Survey Current Situation: US Survey UK Survey Exchange samples for each method comparison separately Adjust survey data for differences in calibration Ireland Survey Germany Survey Compare adjusted survey data 22

23 Comparison of Data across Several Labs or Countries is Easy after Standardization US Survey Canada Survey Reference UK Survey Future situation: One-time exchange of samples to achieve common calibration No further comparison or adjustment of survey data needed Ireland Survey Germany Survey 23

24 Standardization of Measurements Vitamin D Example NIST NIST, CDC Pure Compound Reference Material (NIST SRM 2972) Calibrate Mass Spectrometry-Based Reference Method Assign Value Calibration verification Secondary Reference Material (NIST SRM 972) NIH, CDC, NIST, Gent NIH, CDC, NIST, Gent, PH labs, Commercial kit producers Panel of Sera with Assigned Values Calibrate Routine Assays Assign Value CDC Vitamin D Standardization Coordinating Center Users Patient Samples 24

25 Maintaining Quality Measurements UK DEQAS Clinical & research labs, commercial kit producers NIST VitDQAP Clinical & research labs, commercial kit producers CDC LC-MS/MS Candidate Reference Method CAP Bone & Growth Survey Clinical labs, commercial kit producers NIH-CDC Vit D Standardization Program Selected PH labs 25

26 What do we Need to Ensure Continued High Quality Measurements? Use method anchored to accuracy-based traceability chain Establish and follow detailed SOPs Train staff well in all procedures Include internal quality control samples in every run Participate in external quality assurance programs Use reference materials on a regular basis 26

27 Ultimate t goals of improved measurements: Better diagnosis and treatment: Better assessment of the vitamin D status of the individual and populations More reliable prevalence estimates of inadequate levels Help reduce or prevent negative health outcomes: Better estimation of optimal levels of 25(OH)D for various health outcomes 27

28 Acknowledgments CDC/NCEH: o o Rosemary Schleicher and her vitamin D laboratory team Hubert Vesper - CDC Vitamin D Standardization Coordinating Center CDC/NCHS: Anne Looker, David Lacher, Cliff Johnson NIH/ODS: Beth Yetley, Chris Sempos, Paul Coates NIST: Karen Phinney, Steven Wise 28