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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 identify associations of adiposity and physical activity with mortality in older adults to determine if physical activity plays a protective role in this adverse outcome of obesity.

Inclusion Criteria:

National Institute of Health-AARP Diet and Health Study participants who entered the study in 1995-1996
AARP members 50 to 71 years of age
Residing in any of the following US states or cities:
- California, Florida, Louisiana, New Jersey, North Carolina, Pennsylvania
- Atlanta (Georgia), Detroit (Michigan)
Completed both the baseline questionnaire in 1995-1996 and the second questionnaire in 1996-1997, which included full information on waist circumference, BMI and physical activity.

Exclusion Criteria:

Persons with waist circumference less than 60cm
Persons with Body Mass Index (BMI) of less than 18.5 or greater than 60
Persons who reported cancer, cardiovascular disease or emphysema.

Description of Study Protocol:

Recruitment

The cohort consisted of a subset of participants in the National Institutes of Health-AARP Diet and Health Study (older adults ages 50 to 71), who completed two questionnaires. This included information about waist circumference, BMI and physical activity.

Design

Prospective cohort study
The study looked at:
- Mortality rate and hazard ratios of subjects by BMI, waist circumference and physical activity
- Mortality rate and hazard ratios of joint indices, examining:
  - BMI and physical activity
  - Waist circumference and physical activity
  - Data of these joint indices among "never smokers."

Intervention

The study examined the incidence of mortality on various groupings of subjects related to adiposity and physical activity.

Statistical Analysis

Age-standardized mortality rates were calculated to the age distribution in the cohort of subjects using five-year categories
Fitted Cox proportional hazard models were used to estimate the individual and joint ratios of adiposity (BMI and waist circumference) and physical activity on mortality
Adjustments were made for age, sex, race/ethnicity, education, smoking status and alcohol consumption
Adjustments were made for BMI in the joint adiposity analysis
The proportional hazards assumption was not violated.

Data Collection Summary:

Timing of Measurements

Mortality: Annual measures from the Social Security Administration Death Master File and National Death Index from 1996-1997 through December 31, 2006
Anthropometric assessments were all self-reported and collected on questionnaires that were used as part of the study data collection.

Dependent Variables

Mortality.

Independent Variables

BMI:
- Current height and reported weight at age 50, to the nearest pound, were used to calculate BMI
- 18.5 to less than 25
- 25 to less than 30
- 30 to less than 35
- 35 or higher
Waist circumference:
- Self reported, and guided by pictured instruction
- Group 1: Men less than 94cm, women less than 80cm
- Group 2: Men 94 less than 102cm, women 80 less than 88cm
- Group 3: Men 102 less than 110cm, women 88 less than 96cm
- Group 4: Men 110cm or more, women 96cm or more
Physical activity:
- Moderate to vigorous activity was assessed by a question of the average time spent exercising each week in activities involving a moderate amount of exertion
- Vigorous activity was assessed by a question of the average time spent in activities that caused increases in breathing, increases in heart rate or sweating during a typical month in the last 12 months
Moderate physical activity:
- Less than one hour per week
- One to three hours per week
- Four to seven hours per week
- More than seven hours per week
Vigorous physical activity
- Never
- Rarely
- One to three times per month
- One to two times per week
- Three to four times per week
- Five or more times per week.

Control Variables

Age
Sex
Race/ethnicity
Education
Smoking status
Alcohol consumption
BMI in the joint adiposity analysis.

Description of Actual Data Sample:

Initial N: N=185,412 (male and female participants not noted)
Attrition (final N): N=185,412
Age: Participants were 51 to 72 years of age; mean age in years reported only by statistical groups analyzed, which ranged from 59.8 years of age to 63.0 years of age
Ethnicity: Non-Hispanic white was reported only by statistical groups analyzed, which ranged from 91.4% to 94.3%
Other relevant demographics:
- College or post-graduate education was reported only by statistical groups analyzed, which ranged from 32.6% to 48.2%
- "Current smoker" was reported only by statistical groups analyzed, which ranged from 6.7% to 16.7%
Location: Participants recruited were AARP members from: California, Florida, Louisiana, New Jersey, North Carolina, Pennsylvania, Atlanta (Georgia), and Detroit (Michigan).

Summary of Results:

Key Findings

In general:
- Participants with the highest measures of adiposity (BMI and waist circumference) had a lower educational level, were less physically active, were less likely to currently smoke and had lower alcohol intake than persons with a normal BMI or waist circumference
- Compared to normal weight, participants who were overweight, obese and morbidly obese were associated with significantly greater mortality risk, as were participants in the two highest groupings of waist circumference
- Inactive subjects had a more than 50% greater mortality risk than those with the highest amount of physical activity
- Overweight, obesity, a large waist circumference and low physical activity were each independent predictors of mortality
- Compared with normal-weight persons who were physically active (more than seven hours per week of moderate physical activity), mortality risks were 1.62 (95% confidence interval: 1.50 to 1.75) for inactive normal-weight persons, 1.79 (95% confidence interval: 1.37 to 2.33) for active morbidly obese persons, and 3.45 (95% confidence interval: 2.79 to 4.00) for inactive morbidly obese persons
- Similar results were found for the combined relation of BMI and vigorous physical activity
- Inactive persons with a large waist circumference had two times greater mortality risk than active persons with a normal waist circumference
- High physical activity attenuated but did not eliminate the increased mortality risk associated with obesity
In joint relationships among groups, with BMI:
- Differences among sex was not significant and all results for both men and women were combined
- In each BMI group, the mortality rate increased with decreasing levels of physical activity
- In each physical activity group, mortality rose with increases in BMI; there was no attenuation of this obesity effect with physical activity
- With the benchmark of the group with normal BMI and the most moderate physical activity (more than seven hours per week), mortality risk was significantly increased in groups with lower physical activity levels within the same BMI range
- In the most active group, mortality risks increased as obesity increased
- With regards to "never smokers" compared to active, normal-weight persons, active obese had a two times higher mortality risk, and active morbidly obese had a three times greater mortality risk
In joint relationships among groups, with waist circumference:
- In comparison with the most active persons with a normal waist circumference, mortality risk increased with increased waist circumference as well as with decreasing physical activity
- Inactive persons with a normal waist circumference had about the same mortality risk as the most active persons with the highest waist circumference.

Author Conclusion:

Highest mortality risks were found among inactive morbidly obese older individuals, as well as inactive individuals with a large waist circumference. Physical activity eased but did not negate the increased mortality risk associated with obesity. With older individuals, promotion of physical activity and weight gain prevention could help lower their risk of mortality.

Funding Source:

Government:

National Institutes of Health, National Cancer Institute, National Institute on Aging

Reviewer Comments:

All of the anthropometrics and physical activity levels were self-reported and as such may be under-reported or misrepresented in the dataset, possibly causing misclassification of subjects into groups
The BMI was calculated at 50 years of age, thus the actual effects of BMI on mortality may not have been demonstrated
Subjects appear to be a representative sample of the AARP population from the geographic recruitment areas, but may not be representative of the older US population in general. Demographic information shows upwards of 90% of the sample was "non-Hispanic White."

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?		No
	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.)	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%.)	N/A
	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?		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?	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?		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?	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