FNOA: Assessment of Overweight/Obesity (2012)

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

To examine the association between waist circumference and all-cause mortality.

Inclusion Criteria:
  • Participated in the NIH-AARP Diet and Health Study
  • Completed both a baseline questionnaire and follow-up questionnaire
  • Provided a complete data set including waist circumference and height and weight.
Exclusion Criteria:
  • Did not participate in the NIH-AARP Diet and Health Study
  • Did not complete both the baseline and follow-up questionnaires
  • Did not provide a complete data set including waist circumference and height and weight
  • Reported a waist circumference of less than 60cm
  • Had a BMI of less than 15kg/m2 or greater than 60kg/m2.
Description of Study Protocol:

Recruitment

The NIH-AARP Diet and Health Study began in 1995-1996 when an extensive baseline questionnaire was mailed to AARP members aged 50-71 years who resided in one of six states (California, Florida, Louisiana, New Jersey, North Carolina and Pennsylvania) or one of two metropolitan areas (Atlanta, Georgia or Detroit, Michigan). 

Design

Prospective cohort study 

Blinding used

None 

Intervention

Not applicable 

Statistical Analysis

Cox proportional hazards models were fitted to study the associations between sex-specific quintiles of waist circumference and time to death in men and women. Model 1 adjusted for age. Model 2 additionally adjusted for racial/ethnic group, education, smoking status, physical activity, alcohol consumption and height. Model 3 included BMI as a measure of relative weight to assess the impact of waist circumference on mortality independent of BMI. 

Data Collection Summary:

Timing of Measurements

Two questionnaires were self-completed by participants. The first was administered at baseline in 1995-1996. The second was completed in 1996-1997 for collection of additional data on diet, family history of cancer, anthropometric measures (including waist circumference), physical activity and use of hormone replacement therapy

Dependent Variables

Mortality was determined from 1996-1997 to December 31st, 2005 by annual linkage of the cohort to the Social Security Administration Death Master File.

Independent Variables

  • Waist circumference (self-measured using pictured instruction to measure their waist with a tape measure 1 inch above the navel while standing and to report values to the nearest quarter inch
  • Self reported height and weight
  • Calculated BMI.

Control Variables

  • Age
  • Racial/ethnic group
  • Educational attainment
  • Smoking history
  • Physical activity
  • Prevalent chronic disease (cancer, heart disease, stroke, diabetes, emphysema, renal failure).

 

Description of Actual Data Sample:
  • Initial N: 245,533 participants
    • 154,776 men
    • 90,757 women
  • Attrition (final N): All were included in the final analysis
  • Age: 50-71 years at baseline
  • Ethnicity: Majority (greater than 90%) were non-Hispanic white 
  • Other relevant demographics: Men and women in the highest quintile of waist circumference had a lower level of education, were less likely to currently smoke, were less physically active, had a slightly lower alcohol intake and had a higher prevalence of disease than those with a lower waist circumference
  • Anthropometrics: No significant differences at baseline
  • Location: Six states and two metropolitan areas
    • California
    • Florida
    • Louisiana
    • New Jersey
    • North Carolina
    • Pennsylvania
    • Atlanta, Georgia
    • Detroit, Michigan.

 

Summary of Results:

Key Findings

  • Subjects in the highest quintile of waist circumference had an approximately 50% higher risk of mortality than persons in the second quintile of waist circumference (reference group) (men: hazard ratio (HR)=1.51, 95% CI=1.44-1.57; women: HR=1.56, 95% CI=1.44-1.68)
  • After adjustment for BMI, subjects in the highest quintile of waist circumference still had a significantly higher death risk than subjects in the second quintile (reference group) (men: HR=1.22, 95% CI=1.15-1.29; women: 1.28, 95% CI=1.16-1.41)
  • The association between waist circumference and mortality was J-shaped. Men in the lowest waist circumference quintile had approximately 5-10% higher risk of mortality than those in the reference group (HR=1.10, 95% CI=1.04-1.15). This relationship was not significant in women
  • Prevalent disease did not change the relationship in multivariate analysis
  • A significant interaction was seen between smoking status and waist circumference was found in both men and women. The association between large waist circumference and mortality was stronger in never smokers than in former or current smokers.
  • The results varied by race/ethnic group. No significant association was observed between waist circumference and mortality in non-Hispanic Blacks. Large waist circumference was associated with a higher mortality rate in Hispanic men, but not in Hispanic women. In Asian men, a significant association was found between the fourth quintile of waist circumference and mortality, but not between the highest quintile of waist circumference and mortality. No significant associations were observed for Asian women. 
Author Conclusion:
  • A large waist circumference was associated with an approximately 50% increased risk of mortality in both men and women
  • Even after adjustment for BMI and other covariates, a large waist circumference remained associated with an approximately 25% increased mortality risk.
Funding Source:
Government: National Institutes of Health, National Cancer Institute and National Institute on Aging
Reviewer Comments:

All of the anthropometrics and physical activity levels were self-reported and as such may be underreported or misrepresented in the dataset possibly causing misclassification of subjects into groups.

BMI was calculated at 50 years of age, thus the actual effects of BMI on mortality may not have been demonstrated.

The study population was over 90% non-Hispanic white. When results were stratified by racial/ethnic group, the relationship between waist circumference and mortality for non-Hispanic whites was nearly identical to the results for the entire study population. Only a weak association was noted in the association between waist circumference and mortality for non-Hispanic Blacks and no association was found between the highest quintile for waist circumference and mortality in Asian men. Small sample size may likely play a role in these observations. Results should be generalizable for a population of non-Hispanic white adults aged 50-71 years, but may not be generalizable for populations of older non-Hispanic Blacks, Asians and Hispanics.

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? ???
  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? No
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? N/A
  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? No
  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.) No
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? No
  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? Yes
  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? ???
  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? ???
  7.5. Was the measurement of effect at an appropriate level of precision? ???
  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? Yes
  10.2. Was the study free from apparent conflict of interest? Yes