National Health and Nutrition Examination Survey NHANES

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National Health and Nutrition Examination Survey
(NHANES) Environmental Exposure Data Susan
Schober, Ph.D.
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OUTLINE

• NHANES - brief background
• NHANES environmental exosure biomonitoring
• National Report on Human Exposure to
  Environmental Chemicals
• Additional resources
• Statistical considerations
• Interpretation of results - health effects?

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NHANES

• Provides objective measures of health and risk
  factors
• To assess the health and nutritional status of
  adults and children in the United States through
  household interviews, physical examinations, and
  laboratory tests

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National Health and Nutrition
Examination Surveys
Survey
Dates
Ages
NHES I 1960-62 18-79 years NHES II 1963-65 6-11
years NHES III 1966-70 12-17 years NHANES
I 1971-75 1-74 years NHANES II 1976-80 6 mo.-74
years HHANES 1982-84 6 mo.-74 years NHANES
III 1988-94 2 mo. NHANES 1999- All ages
OP96S025
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NHANES Background

• Cross-sectional survey
• Complex, multistage sample design
• Representative of the civilian, household
  population of the US
• Oversample specific demographic groups
  (e.g.,blacks, Mexican Americans)

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NHANES Background, cont.

• Beginning in 1999, annual samples and continuous
  data collection
• Data released in 2 year cycles
• Fifteen geographic locations per year
• Annual sample size of 5,000 persons
• Detailed estimates of population subgroups with
  multiple years combination

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Examples of NHANES Data

• Disease or condition prevalence
• Heart disease
• Hypertension
• Diabetes
• Risk factors
• Overweight/obesity
• Smoking
• High cholesterol
• Nutrition monitoring
• Dietary intake
• Dietary supplements vitamins, minerals
• Laboratory measures

• Body measurements
• Height
• Weight
• Growth and development
• Pediatric growth charts
• Disease monitoring
• Trends
• Impact
• Medical care
• Prescribed/OTC drugs
• Environmental exposures

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MEC laboratory

• CBC and differential
• Pregnancy test
• Blood, urine and vaginal swab processing
• 76 different vials of samples
• 26 laboratories
• 300 laboratory assays

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NHANES Overall Response Rates
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NHANES Environmental Exposure Data
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Lead used in gasoline production andaverage
blood lead levels
Lead used In gasoline
Total lead used per 6 month period (1000 tons)
Average blood lead levels (micrograms/deciliter)
Average blood lead levels
1977
1979
1978
1976
1980
SOURCE CDC/NCHS, Second National Health and
Nutrition Examination Survey, 1976-80.
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Environmental measures in NHANES

• NHANES II
• Began measuring blood lead levels
• NHANES III
• Serum cotinine
• Urine cadmium
• Volatile organic compounds (VOCs)
• Non-persistent pesticide metabolites

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Current NHANESEnvironmental Exposure Measures

• Biomonitoring
• The assessment of human exposure to chemicals by
  measuring the chemicals or the breakdown products
  in human specimens, such as blood or urine
• Measures of chemicals in environmental media

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NHANES 1999 Biomonitoring

• Laboratory of CDCs National Center for
  Environmental Health
• Technical advances in laboratory methods
• Small volumes of specimen
• Measurements in the parts per billion or parts
  per trillion range
• National Report on Human Exposure to
  Environmental Chemicals

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National Report on Human Exposure to
Environmental Chemicals

• Identify chemicals to which people are exposed
• Establish reference ranges for the US population
• Study secular trends
• Examine prevalence of exposure above known
  toxicity levels
• Describe variation by sociodemographic factors
• Set priorities for future research

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Second Report on Human Exposure to Environmental
Chemicals n 116

• Metals
• Polychlorinated biphenyls, dioxins and furans
• Organochlorine pesticides
• Carbamate pesticides
• Organophosphate pesticides
• Herbicides
• Polycyclic aromatic hydrocarbons
• Phthalates
• Phytoestrogens
• Pest repellants
• Cotinine

www.cdc.gov/exposurereport
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Third Report on Human Exposure to Environmental
Chemicals

• 38 new chemicals
• One new class
• Pyrethroid pesticides
• Additions w/in class
• PAHs
• Aldrin, dieldrin, endrin
• Phthalate metabolites
• Dioxins, furans and PCBs
• Pesticides and herbicides

www.cdc.gov/exposurereport
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Table 11. Cadmium in urine (creatinine corrected)
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4th National Report on Human Exposure to
Environmental Chemicals

• Data from NHANES 2003-2004
• 275 chemicals
• Priority chemicals initial results published in
  peer-reviewed literature
• Tentative date for Fourth Report Summer 2008

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NHANES 2003-2004Priority chemicals

• Perchlorate
• Polybrominated diphenyl ethers
• Perfluorinated chemicals
• Environmental phenols
• Arsenic

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Measures of chemicals in environmental media,
NHANES 1999

• Volatile organic compounds
• Personal exposure monitors (1999-2001)
• Household water (selected chemicals)
• Lead
• Household dust samples
• Allergens
• Household dust samples
• Perchlorate
• Household water

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Additional resources for NHANES analyses

• Geocoded data
• Mortality follow-up
• Stored specimens for future research
• DNA

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NHANES data at the RDC(Research Data Center)

• STDs and mental health data on children
• Any geographic information (geocoding)
• Details such as more detailed occupational coding

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NCHS Research Data Center (RDC)

• http//www.cdc.gov/nchs/rd/rdc.htm
• Detailed information
• RDC operations and process
• Proposal submissions
• Researcher supplied data

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NCHS Research Data Center (RDC)

• Data access
• Guest research (on-site)
• Remote access
• RDC staff-assisted research
• Costs

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Geographic linked analysis example
Pickett MS, Schober SE, Brody DJ, Curtin LR,
Giovinio G. Smoke-free laws and second hand smoke
exposure in US adults, 1999-2002. Tobacco Control
200615302-307
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Trends in median serum cotinine levels among
non-smokers by age group, 1988-1991 to 2001-2002
1988-1991
1991-1994
2001-2002
1999-2000
SOURCE CDC/NCHS, NHANES III, NHANES 1999-2002
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American Nonsmokers Rights Foundation

• Database of local and state indoor air ordinances
• Laws covering workplaces, restaurants, and bars
• State, county, and city levels
• Laws enacted through the end of the calendar year
  preceding the survey year

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Smoke-free law coverage categories

• Extensive coverage
• At least one smoke-free law (workplace,
  restaurant, or bar) at county or state level
• Limited coverage
• No state or county smoke-free law but at least
  one in one or more municipalities within the
  county
• No coverage

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Smoke-free laws and secondhand smoke exposure

• Survey participants classified according to
  smoke-free law coverage in their county of
  residence
• Survey locations are not disclosed

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Plt0.05
Note SHS exposure defined as serum cotinine gt
0.05 ng/ml
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NHANES III Mortality Follow-up Example
Schober SE, Mirel LB, Graubard BI, Brody DJ,
Flegal KM. Blood lead levels and death from all
causes, cardiovascular disease, and cancer
Results from the NHANES III Mortality Study.
Environ Health Perspect 20061141538-1541
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Relative risk for all-cause, cardiovascular, and
cancer mortality by blood lead category
Cardiovascular disease
All causes
Cancer

• lt5 µg/dL 1
  1 1
• 5-9 µg/dL 1.24 (1.05-1.48) 1.20
  (0.93-1.55) 1.44 (1.12-1.86)
• gt10 µg/dL 1.59 (1.28-1.98) 1.55
  (1.16-2.07) 1.69 (1.14-2.52)

NOTE Numbers in parentheses are 95
confidence intervals Relative
risks adjusted for sex, race/ethnicity,
education, and smoking status
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Relative risk of all cause mortality for
different blood lead levels
Note referent level of 1.5 µg/dL (12.5th
percentile)
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Statistical Considerations
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Statistical Considerations

• Subsamples
• Small sample size
• Small number of geographic locations and
  reliability of estimates
• Limit of detection (LOD)
• Large proportion of results ltLOD
• Variable detection limits

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Limit of detection (LOD)

• Proportion of results lt LOD varies from 0 to 100
• Choice of fill value for results below the LOD
  can influence parametric estimates
• NHANES uses LOD/square root of 2
• LOD is variable for some analytes
• May be a wide overlap of values for detectable
  and non-detectable results

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If proportion ltLOD is high

• Limits statistical estimates that can be reported
  
• Rule if more than 40 of results are ltLOD,
  geometric mean is not calculated
• In 2nd Exposure Report, all values less than the
  highest limit of detection were treated as below
  the limit of detection
• Percentile estimates indicated by ltLOD.

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Interpretation of biomonitoring measures
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NHANES environmental exposuremeasures --
strengths

• First US population-based estimates of exposure
  to a wide range of environmental chemicals
• Objective measure of exposure chemical or
  metabolite in the body
• Critical information for environmental risk
  assessments, monitoring environmental exposures,
  and prioritizing further research of potential
  health effects from environmental exposures

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NHANES biomonitoring -- some limitations

• Cannot use data to pinpoint at-risk
  communities
• Limited questionnaire data - limits understanding
  of sources of exposure
• Criteria for defining health based cutoffs are
  not available for most chemicals

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NHANES Mercury ComponentFish and Shellfish
consumption

• During the past 30 days, did you eat any types
  of fish (shellfish) listed on this card? Include
  any foods that had fish (shellfish) in them such
  as sandwiches, soups, or salads.
• Questions on fish and shellfish asked separately
• Cards with list of specific species and other
  and unknown categories

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Selected Percentiles of Total Blood Mercury Women
16-49 years
NOTE NHANES 1999-2000 SOURCE CDC/NCHS
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Relating results to health risks

• Detection of chemical does not indicate a
  potential health effect
• Criteria for defining health based cutoffs are
  not available for most chemicals.
• Blood lead is a notable exception
• Occupational standards exist for some
  biomeasures, but extrapolation to environmental
  exposure is problematic

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Environmental exposuresReport of Findings
Blood metals

• Cadmium gt5.0 ng/ml
• Lead
• 1-5years gt10.0 ug/dL
• 6-17 years gt10.0 ug/dL
• gt18 years gt10.0 ug/dL
• Mercury
• Females 1-49 years gt5.8 ug/L
• Females gt50 years gt10.0 ug/L
• Males 1-17 years gt5.8 ug/L
• Males 18 years gt10.0 ug/L

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NHANES biomonitoring measuresInterpreting results

• Further research is needed to
• Define health risks associated with specific
  biomonitoring meaures
• Define the relationships between biomonitoring
  measures and other measures of environmental
  exposure
• Further understand toxiconetics of environmental
  chemicals
• NHANES and Exposure Report help set priorities
  for future research

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Websites

• NHANES
• www.cdc.gov/nchs/nhanes.htm

National Report on Human Exposure to
Environmental Chemicals www.cdc.gov/exposurereport
Summary of NHANES content www.cdc.gov/nchs/data/nh
anes/survey_content_99_08.pdf
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National Academy of Sciences ReportToxicological
Effects of Methylmercury

• BMDL 58 µg/L in cord blood
• EPA reference dose 0.1 µg/kg per day
• Incorporates an uncertainty factor of 10
• Equivalent to 5.8 µg/L in maternal blood?