EAL

FNOA: Assessment of Overweight/Obesity (2012)

Citation:

Study Design:

Class:

- Click here for explanation of classification scheme.

Quality Rating:

Research Purpose:

To test the hypothesis that older, community-dwelling individuals who are very obese would have greater mortality than normal or thin individuals.

Inclusion Criteria:

Participation in the Longitudinal Study of Aging with baseline interview in 1984
Non-institutionalized individuals
Age 70 or older.

Exclusion Criteria:

Not a participant in LSOA study
Younger than 70 years of age
Institutionalized status.

Description of Study Protocol:

Recruitment

Recruitment methods for the LSOA not discussed.

Design

Retrospective cohort study:

Baseline interviews for the LSOA were conducted in individuals' homes, with family members interviewed if participants were unable to answer the survey
Data obtained from the initial LSOA study in 1984 was used
Mortality and obesity were the variables of interest. Mortality information was obtained from the linked National Death Index for the LSOA population for eight years from the beginning of the study
BMI was calculated using self-reported heights and weights. Individuals were placed into one of three groups dependent on BMI for analysis
Variables used to construct multivariable models of mortality were guided by the behavioral model of health services utilization:
- Model one: Baseline weight and mortality data
- Model two: Baseline plus poverty data
- Model three: Beginning with subjects alive two years after initial survey
- Model four: Baseline plus controls for self-reported serious medical conditions
- Model five: Subset of model one, including only those without serious medical comorbidities at baseline.

Statistical Analysis

Cox proportional-hazards analysis to assess associations between BMI and mortality
Statistical significance assessed at P=0.05 level.

Data Collection Summary:

Timing of Measurements

Baseline information collected in 1984
Survival measured for eight years from the beginning of the survey in January 1984 until December 1991 using the National Death Index
BMI calculated using self-reported height and weight collected at baseline.

Dependent Variables

Mortality.

Independent Variables

Obesity.

Control Variables

Demographics including age, sex, race and region of country
Ethnicity
Education level
Health insurance status
Level of ability to care for self
Health services utilization
Income
Self-reported medical conditions.

Description of Actual Data Sample:

Initial N: 7,527 subjects
Attrition (final N): 7,459 subjects provide information to match the National Death Index (62% female, 38% male)
Age: 76.8±5.59 years
Ethnicity: 91.4% white, 7.4% black, 2.9% Hispanic, 1.2% other
Other relevant demographics:
- 17.7% of subjects with income level below the poverty threshold
- Over one-third of subjects lived alone
- 72% of subjects had private insurance
Anthropometrics:
- BMI 24.4±4.33kg/m²
- Men had statistically significantly higher BMI than women (24.56±3.64kg/m² vs. 24.3±4.72kg/m² SD; P=0.127)
- BMI values for women appeared less normally distributed with a broader tail at high BMI values
- Body mass variables (7,397 subjects)
  - Thin (lowest 10% of BMI distribution): 9.9%
  - Normal weight (not classified as thin or obese): 75%
  - Obese (highest 15% of BMI distribution): 15%
Location: United States.

Summary of Results:

Key Findings

38.5% of subjects died between January 1984 and December 1991
Kaplan Meier survival curves across the thin, normal and obese weight categories show highest mortality among the thin group and lowest in the obese group
Highly significant differences across weight categories (F=52.34, P<0.001); thin group had highest mortality (53.9%) of the three weight categories whereas the obese group had the lowest (33.5%)
Incorporating the poverty indicator (in model two) strengthened relationships between increased BMI and decreased mortality
Model three eliminated the first two years of mortality reduced the number of deaths available for modeling, which resulted in significantly lower mortality in the obese group at 83 months of follow-up, but by 96 months mortality in the obese group was no longer significantly different (hazard ratio 0.93; 95% CI: 0.82 to 1.06, P=0.27)
Model four, addition of self-report medical conditions, results were only marginally different from models one or two
Model five, included those healthy at baseline, obesity was strongly associated with lower mortality (hazard ratio=0.67, 95% CI: 0.51 to 0.88), whereas the thin group had higher mortality (hazard ratio=1.4, 95% CI: 1.13 to 1.74).

Model

Hazard Ratio and 95% CI in the Obese Group

P-value

Hazards Ratio and 95% CI in the Thin Group

P-value

Model One: Baseline (N=7,048)

0.86 (0.77 to 0.97)

P=0.011

1.46 (1.30 to 1.64)

P=0.000

Model Two: Baseline plus poverty data (N=5,916)

0.84 (0.74 to 0.95)

P=0.007

1.55 (1.36 to 1.75)

P=0.000

Model Three: Beginning with those alive two years after initial survey (N=6,510)

0.93 (0.82 to 1.06)

P=0.268

1.38 (1.2 to 1.57)

P=0.000

Model Four: Baseline plus controls for self-reported serious medical conditions (N=6,888)

0.83 (0.74 to 0.94)

P=0.002

1.58 (1.41 to 1.78)

P=0.000

Model Five: Subset of model on, including only those without medical condition comorbidities at baseline (N=2,378)

0.67 (0.51 to 0.88)

P=0.004

1.40 (1.13 to 1.74)

P=0.002

Author Conclusion:

In contrast to many studies showing increased mortality in younger obese populations, the analysis of the LSOA suggests a decreased mortality in obese older people
Lower mortality in obese older people persisted despite controlling for many different confounders
Study results add to those of others that suggest weight goals appropriate in younger age groups may be inappropriate for older individuals.

Funding Source:

Government:

National Heart, Lung and Blood Institute, Agency for Health Care Policy Research

Reviewer Comments:

Large, nationally representative sample
Majority of subjects were of white ethnicity; limited diversity of subjects
Did not control for smoking
Self-reported heights and weights introduce possible inaccuracies.

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)	Yes
	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)	Yes

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?	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.)	N/A
	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?	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?	N/A
	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?		No
	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?	No
	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?	No
	7.7.	Were the measurements conducted consistently across groups?	???
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