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FNOA: Assessment of Overweight/Obesity (2012)

Citation:
 
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:

To compare the relative importance and joint association of overall obesity and abdominal adiposity or body fat distribution with risk of total and cardiovascular disease mortality among a nationally representative of US adults and to examine the influence of sex and age on these associations.

Inclusion Criteria:

Participation in the National Health and Nutrition Examination Survey (NHANES III):

  • Civilian
  • Non-institutionalized
  • Minimum age 30 years.

 

Exclusion Criteria:
  • Pregnant
  • Individuals with height, weight or body measurements missing
  • Individuals with insufficient identifying information available for follow-up.
Description of Study Protocol:

Recruitment

Initial data were taken from the NHANES III study during the period of 1988 to 1994. Participant mortality was followed by the NHANES III Mortality Study through December 31, 2000.

Design

Prospective cohort study. Subjects were analyzed on many criteria related to obesity and mortality, including BMI, cholesterol values, exercise, alcohol use, age and more. Participants were followed from enrollment in the NHANES III study until death or December 31st, 2000. The cohorts therefore were men vs. women, and subgroups of decedents vs. survivors. The participants were ages 30-102 at baseline, and were stratified into middle aged (30-64) and older adults (65 or more).

Blinding used

Implied with measurements

Intervention

Not applicable

Statistical Analysis

  • All analyses were weighted to match the characteristics of US so that the final data sample is representative of the country population. The authors did not make statistical adjustments for physical activity.
  • Multivariable cox proportional hazards regression models were used to examine the relation of adiposity with mortality after adjustment for potential confounders. Physical activity was not adjusted for in this model.
  • Linear trends were examined with the inclusion of adiposity as an ordinal variable within the multivariable models
  • All tests of hypotheses were based on a type I error rate of 0.05 using two-sided tests
  • Data were analyzed using SAS-callable SUDAAN statistical software, release 9.0.

 

Data Collection Summary:

Timing of Measurements

Data were taken from the NHANES III survey from 1988 to 1994. The subjects were followed until their death or until December 31, 2000.

Dependent Variables

  • Vital status as of December 31st, 2000 (using the NHANES III Mortality study)
  • Cause of death (International Classification of Diseases, 9th and 10th revisions).

Independent Variables

  • Age (middle aged=30-64, older adults ≥65)
  • Body weight (to the nearest 0.1kg using Toledo electronic scale)
  • Standing height (to nearest 0.1cm using Seca stadiometer)
  • BMI (calculated)
  • Waist, hip and thigh circumference (to the nearest 0.1cm using steel measuring tape)
  • Waist-to-hip ratio and waist-to-thigh ratio (calculated).

Control Variables

Baseline Demographics:

  • Race/ethnicity (self reported: "non-Hispanic white", "non-Hispanic African American", "Mexican American", and "other")
  • Education ("less than high school", "high school", "some college" or "college")
  • Smoking ("current", "former" or "never" with individuals having smoked minimum 100 cigarettes, 20 cigars of 20 pipes of tobacco in their lifetime but not currently smoking being classified as former)
  • Alcoholic beverages (assessed as type and frequency over past month).

Medical:

  • Hypertension (average of maximum six seated blood pressure reading my trained professional ≥140/90mmHg)
  • Diabetes (defined by history [type 1 or type 2], use of diabetes medications or fasting blood glucose >126mg/dL)
  • High cholesterol (included total cholesterol ≥240mg/dL or use of lipid lowering medications)
  • Hormone replacement therapy use in women (self reported: "current" or "not current")
  • Heart disease (included angina, physicians diagnosis of congestive heart failure, or myocardial infarction)
  • Other medical history (physician diagnosis of respiratory disease, cancer or stroke).
Description of Actual Data Sample:
  • Initial N: 13,065 adults
  • Attrition (final N): 12,228
    • 5,799 males
    • 6,429 females
  • Age: 30-102 years
    • Men (mean age): 54.6 years
    • Women (mean age): 53.8 years
  • Ethnicity:
    • White: Men 79.1; Women 78.2
    • African American: Men 9.4; Women 10.6
    • Mexican American: Men 4.4; Women 3.8
    • Other: Men 7.1; Women 7.4
  • Other relevant demographics: See Results
  • Anthropometrics: See Results
  • Location: United States.

 

Summary of Results:

Key Findings

  • During a 12-year follow-up (102,172 person-years), 1,188 and 925 women died
  • Measures of abdominal obesity or body fat distribution, particularly waist-to-hip ratio (WHR) and waist-to-thigh ratio (WTR) were strongly and positively associated with risk of total mortality in middle aged (30-64 year old) adults (P<0.01 for both men and women)
  • WHR was a better predictor for women (P for trend=0.001). This relationship existed even after adjustment for BMI.
  • BMI and waist circumference exhibited U- or J-shaped associations
  • Risk of mortality increased with a higher waist-to-hip ratio and waist-to-thigh ratio among normal weight (BMI 18.5-24.9kg/m2) and obese (BMI >30.0kg/m2) adults
  • In older adults (age 65-102 years) a higher BMI in both sexes (P for trend=0.05) and waist circumference in men (P for trend=0.001) were associated with increased survival, while remaining measures of body fat distribution exhibited either no association or an inverse relation with mortality.

  Men Women
  Decedents Survivors Decedents Survivors
Education (years)  11.2 (0.2)  12.3 (0.1)*  11.3 (0.3)  12.1 (0.1)*
Physical activity (times per month) 23.7 (1.6)  27.2 (0.9)* 15.0 (1.7)  21.1 (0.7)*
Alcohol use (days pe month) 12.8 (1.6) 12.0 (0.5) 5.5 (1.7) 5.2 (0.4)
Current smoker (%) 44.6

28.2*

 34.6 20.1*
Heart disease (%) 23.0 10.2* 15.4 8.6*
Stroke (%) 6.3 2.5* 6.0 2.1*
Respiratory disease (%) 13.5 8.2* 19.4 8.9*
Cancer (%) 6.6 3.8* 10.4 6.5
Hypertension (%) 42.5 34.7* 42.0 34.1*
High cholesterol (%) 22.3 22.8 30.0 28.9
Diabetes  16.6 8.4* 15.6 6.3*

  *P<0.05 for the sex-specific comparison of those who died to those who were alive at the end of follow-up

 

  Men Women
  Decedents Survivors Decedents Survivors
BMI
 26.7 (0.4) 27 (0.1) 27.6 (0.4) 27 (0.2)
Waist circumference (cm) 98 (1) 98.2 (0.3) 93.1 (1) 91.1 (0.4)*
Hip circumference (cm) 99.4 (0.8) 100 (0.2) 103.3 (.9) 103.1 (0.3)
Thigh circumference 47.7 (0.2) 51.3 (0.1)* 48.3 (0.2) 52.1 (.01)*
Waist-to-hip ratio 0.982 (0.004) 0.983 (0.002) 0.903 (0.007) 0.887
(0.002)*
Waist-to-thigh ratio 2.060 (0.006) 1.899
(0.003)*		 1.962 (0.008) 1.800
(0.003)*

*P<0.05 for the sex-specific comparison of those who died to those who were alive at the end of follow-up

 

Author Conclusion:

In conclusion, ratio measures of body fat distribution are strongly and positively associated with mortality and offer additional prognostic information beyond BMI and waist circumference in middle-aged adults. A higher BMI in both sexes and waist circumference in men were associated with increased survival in older adults, while a higher waist-to-hip ratio or waist-to-thigh ratio either decreased or did not influence risk of death.

Funding Source:
University/Hospital: Johns Hopkins, San Diego State University, University of San Diego
Reviewer Comments:
  • Nationally representative sample. Sampling was described as a "national complex, multistage, clustered, stratified probability sample of the civilian, non-institutionalized population aged two months and older"
  • Anthropometric indices measured by trained technicians rather than self-report, however, these measurements only measured once at baseline. Authors could not examine whether changes occurred in these variables during follow-up or whether this may have influenced study findings.
  • Assessment of use of hormone replacement therapy was limited to "current" or "not current"; the authors did not discriminate between "never" and "former".
Quality Criteria Checklist: Primary Research
Relevance Questions
  1. Would implementing the studied intervention or procedure (if found successful) result in improved outcomes for the patients/clients/population group? (Not Applicable for some epidemiological studies) N/A
  2. Did the authors study an outcome (dependent variable) or topic that the patients/clients/population group would care about? Yes
  3. Is the focus of the intervention or procedure (independent variable) or topic of study a common issue of concern to dieteticspractice? Yes
  4. Is the intervention or procedure feasible? (NA for some epidemiological studies) N/A
 
Validity Questions
1. Was the research question clearly stated? Yes
  1.1. Was (were) the specific intervention(s) or procedure(s) [independent variable(s)] identified? Yes
  1.2. Was (were) the outcome(s) [dependent variable(s)] clearly indicated? Yes
  1.3. Were the target population and setting specified? Yes
2. Was the selection of study subjects/patients free from bias? Yes
  2.1. Were inclusion/exclusion criteria specified (e.g., risk, point in disease progression, diagnostic or prognosis criteria), and with sufficient detail and without omitting criteria critical to the study? Yes
  2.2. Were criteria applied equally to all study groups? Yes
  2.3. Were health, demographics, and other characteristics of subjects described? Yes
  2.4. Were the subjects/patients a representative sample of the relevant population? Yes
3. Were study groups comparable? Yes
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) Yes
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? Yes
  3.3. Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.) N/A
  3.4. If cohort study or cross-sectional study, were groups comparable on important confounding factors and/or were preexisting differences accounted for by using appropriate adjustments in statistical analysis? Yes
  3.5. If case control study, were potential confounding factors comparable for cases and controls? (If case series or trial with subjects serving as own control, this criterion is not applicable.) N/A
  3.6. If diagnostic test, was there an independent blind comparison with an appropriate reference standard (e.g., "gold standard")? N/A
4. Was method of handling withdrawals described? Yes
  4.1. Were follow-up methods described and the same for all groups? Yes
  4.2. Was the number, characteristics of withdrawals (i.e., dropouts, lost to follow up, attrition rate) and/or response rate (cross-sectional studies) described for each group? (Follow up goal for a strong study is 80%.) Yes
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? Yes
  4.4. Were reasons for withdrawals similar across groups? Yes
  4.5. If diagnostic test, was decision to perform reference test not dependent on results of test under study? N/A
5. Was blinding used to prevent introduction of bias? Yes
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? N/A
  5.2. Were data collectors blinded for outcomes assessment? (If outcome is measured using an objective test, such as a lab value, this criterion is assumed to be met.) Yes
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? Yes
  5.4. In case control study, was case definition explicit and case ascertainment not influenced by exposure status? N/A
  5.5. In diagnostic study, were test results blinded to patient history and other test results? N/A
6. Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were interveningfactors described? Yes
  6.1. In RCT or other intervention trial, were protocols described for all regimens studied? N/A
  6.2. In observational study, were interventions, study settings, and clinicians/provider described? Yes
  6.3. Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect? Yes
  6.4. Was the amount of exposure and, if relevant, subject/patient compliance measured? N/A
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? N/A
  6.6. Were extra or unplanned treatments described? N/A
  6.7. Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups? Yes
  6.8. In diagnostic study, were details of test administration and replication sufficient? N/A
7. Were outcomes clearly defined and the measurements valid and reliable? Yes
  7.1. Were primary and secondary endpoints described and relevant to the question? Yes
  7.2. Were nutrition measures appropriate to question and outcomes of concern? Yes
  7.3. Was the period of follow-up long enough for important outcome(s) to occur? Yes
  7.4. Were the observations and measurements based on standard, valid, and reliable data collection instruments/tests/procedures? Yes
  7.5. Was the measurement of effect at an appropriate level of precision? Yes
  7.6. Were other factors accounted for (measured) that could affect outcomes? Yes
  7.7. Were the measurements conducted consistently across groups? Yes
8. Was the statistical analysis appropriate for the study design and type of outcome indicators? Yes
  8.1. Were statistical analyses adequately described and the results reported appropriately? Yes
  8.2. Were correct statistical tests used and assumptions of test not violated? Yes
  8.3. Were statistics reported with levels of significance and/or confidence intervals? Yes
  8.4. Was "intent to treat" analysis of outcomes done (and as appropriate, was there an analysis of outcomes for those maximally exposed or a dose-response analysis)? N/A
  8.5. Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)? Yes
  8.6. Was clinical significance as well as statistical significance reported? Yes
  8.7. If negative findings, was a power calculation reported to address type 2 error? N/A
9. Are conclusions supported by results with biases and limitations taken into consideration? Yes
  9.1. Is there a discussion of findings? Yes
  9.2. Are biases and study limitations identified and discussed? Yes
10. Is bias due to study's funding or sponsorship unlikely? Yes
  10.1. Were sources of funding and investigators' affiliations described? ???
  10.2. Was the study free from apparent conflict of interest? Yes