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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 BMI, WHR and WC as predictors of mortality during a longer period (12 years) in a cohort of older Americans selected to be high-functioning (i.e., who are not frail and less likely to have had recent weight loss that might confound the obesity-mortality association).

Inclusion Criteria:
  • Non-institutionalized 70- to 79-year-old men and women at baseline 
  • Identified to be in the top tertile of functioning for four criteria of physical functioning and two criteria of cognitive functioning:
    • No self-reported disability on the Katz Activities of Daily Living scale
    • No more than one disability on the Rosow and Breslau and Nagi self-reported scales of disability in physical function
    • Ability to hold a semi-tandem balance for at least 10 seconds
    • Ability to stand up from a seated position five times within 20 seconds
    • Score of six or better on the nine-item Short Portable Mental Status Questionnaire
    • Ability to recall three or more of six elements from a short story after delay.
Exclusion Criteria:
  • Adult men and women less than 70 years old or more than 79 years old at baseline
  • Institutionalized men and women aged 70 to 79 years old
  • Men and women aged 70 to 79 years old who failed to score in the top tertile of functioning for four criteria of physical functioning and two criteria for cognitive functioning.
Description of Study Protocol:

Recruitment

  • More than 4,000 non-institutionalized 70- to 79-year-old men and women from the communities of Durham, NC; East Boston, MA; and New Haven, CT, were screened to identify those who were relatively high functioning based on four physical and two cognitive inclusion criteria
  • Of the 1,313 individuals who met all six criteria, 1,189 individuals (91%) agreed to participate and provided informed consent. 

Design

Retrospective cohort study; researchers analyzed data from the longitudinal MacArthur Successful Aging Study. 

Blinding Used

Implied with measurements. 

Statistical Analysis

  • Researchers examined 12-year, all-cause mortality risk by BMI, WC and WHR
  • Proportional hazards regression analysis was used to adjust for gender, race, baseline age and smoking status
  • Sensitivity analyses were conducted in which researchers excluded individuals who died in the early part of the study (first 2.5 years and first seven years) and examined mortality in the later years to remove possibility of confounding due to recent weight loss in those who are close to death 
  • Interaction testing was conducted to determine if the relationship between anthropometric measures (i.e., WC and WHR) to total mortality differs by gender. The researchers also tested for interactions with current smoking status. Based on the results of interaction testing, the obesity-mortality relationship was further examined using stratification analyses.

 

Data Collection Summary:

Timing of Measurements

  • Baseline data including self-reported demographics, chronic conditions and health behaviors were collected starting in 1988. Data obtained by self-report included: age, gender, ethnicity (white vs. black), current smoking status, pack-years of smoking exposure, height and body weight
  • Follow-up data were collected after a mean interval of 28 months, starting in 1991 and again after a mean interval of 57 months from the first follow-up starting in 1995. Deaths were identified via contact with next of kin in 1991 and 1995 at the time of follow-ups, ongoing monitoring of obituary notices and a National Death Index search for deaths up to the year 2000.

Dependent Variables

  • All-cause mortality risk (percentage)
  • Adjusted mortality ratio. 

Independent Variables

  • BMI computed as weight (in kg) divided by square of the height (in meters squared)
  • WC measured at baseline using procedures outlined in the 1988 Anthropometric Standardization Reference Manual 
  • WHR computed as the ratio of WC to hip circumference; waist and hip circumference measured at baseline using procedures outlined in the 1988 Anthropometric Standardization Reference Manual.    

Control Variables

Adjustments to baseline measures of obesity (BMI, WC, WHR) were made to determine mortality associations based on:

  • Age at baseline
  • Gender
  • Race
  • Current smoking status and total pack-years.

 

Description of Actual Data Sample:
  • Initial N: 1,189 (530 males, 659 females)
  • Attrition (final N): 697 (246 males, 451 females); attrition based on all deaths (N=492) as of 2000. Note: There were 71 deaths by 1991, an additional 202 deaths by 1995 and another 219 deaths by 2000. 
  • Age: Average age of participants 74 years for both men and women
  • Ethnicity: 81% white (N=960; 438 men, 522 females)
  • Other relevant demographics:
    • 15% current smokers (17% men, 15% women)
    • Average pack-years smoking: 22 years (33 years for men, 14 years for women)
  • Anthropometrics: BMI was similar in men and women (mean = 26 in both). Mean WC and WHR were greater in men than in women:
    • WC: 38.5cm (men) vs 34.6cm (women)
    • WHR: 0.94 (men) vs. 0.84 (women)
  • Location: Durham, NC; East Boston, MA; and New Haven, CT.
Summary of Results:

Key Findings

  • There was no association between all-cause mortality and BMI or waist circumference in either adjusted or unadjusted analyses
  • Unadjusted 12-year all-cause mortality as a function of obesity indices (BMI, WC, WHR):
    • Mortality risk increased with measures of central obesity, WC (P=0.01) and WHR (P<0.0001). Increase in mortality risk was more pronounced for WHR vs. WC
    • Mortality risk was approximately constant over the range of BMI (P= 0.17) 
  • Adjusted mortality hazard as a function of obesity indices (1988) with adjustment for age, sex, race and smoking:
    • WHR showed a monotonically increasing association with mortality rate [P=0.06 (mortality after 1988), P=0.15 (after 1991), P=0.07 (after 1995)]
    • WC had neither monotonic nor U-shaped associations with mortality [P=0.6 (mortality after 1988), p=0.7 (after 1991), P=0.8 (after 1995)]
    • BMI had neither monotonic nor U-shaped associations with mortality [P=0.3 (mortality after 1988), p=0.5 (after 1991), p=0.8 (after 1995)]  
  • Sensitivity analyses were used to exclude those who died before the first follow-up in 1991
    • Only WHR showed a near-monotonic relationship after 1991; WC and BMI had neither monotonic nor U-shaped associations
    • Only WHR showed near-monotonic associations with mortality after the second follow-up in 1995; WC and BMI showed no consistent pattern
    • Analyses with continuous versions of the obesity measures also confirmed a linear mortality trend with WHR for deaths since baseline, deaths after 1991 and deaths after 1995; there was no linear trend noted for WC and BMI 
  • Interactions and stratified analyses:
    • Gender modified the relationship between continuous WHR and mortality [P=0.04 (mortality after 1988), P=0.07 (after 1991), P=0.6 (after 1995)]
    • Current smoking status did not modify the relationship between WHR and mortality (P>0.6 for smoking interactions)
    • In gender-stratified analyses, there was a strong (graded) relationship between continuous WHR and mortality in women, but not in men.
      • For women, relative hazard after 1988, 1.28 per 0.1 increase in WHR; 95% confidence interval: 1.05 to 1.55; P<0.05
      • For women, relative hazard after 1991, 1.22 per 0.1 increase in WHR; 95% confidence interval, 1.00 to 1.50; P<0.05
      • In men, only the highest category of WHR is more than 1.0 was associated with increased mortality, hazard ratio for mortality after 1995: 1.75, 95% confidence interval, 1.06 to 2.91).
Author Conclusion:

WHR, rather than BMI or WC, appears to be the most appropriate yardstick for obesity-related risk stratification of high-functioning older adults, and possibly all older adults. However, given our use of self-reported weight and height data, these findings need to be confirmed in other cohorts of older adults.

Funding Source:
Government: National Institute on Aging
Reviewer Comments:
  • There is a question whether this cohort is representative of the elderly population due to very large proportion of white subjects (81%). 
  • Authors identified the following strengths and limitations:
  • Strengths: At baseline the cohort represented high-functioning adults, thus minimizing confounding by frailty. Additionally, further confounding by recent weight loss caused by a terminal condition was minimized  by excluding deaths in the first 2.5 years of follow-up (and first seven years in a second sensitivity analysis) with noted minimal effects of these exclusions on the nature of the WHR relationship to mortality.  
  • Limitations:
    • Self report of height and weight may have led to an under-estimation of BMI due to tendency of reporting peak height from younger ages and tendency of overweight individuals to underestimate body weight. This would have strengthened a BMI mortality gradient if present. However, no such gradient was observed in this study.
    • The study was based on single measures of BMI, WC and WHR at one point in time, which limits ability to draw inferences regarding the effect of changing body size on mortality.

 

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? ???
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.) Yes
  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? ???
  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