EAL

FNOA: Assessment of Overweight/Obesity (2012)

Citation:

Study Design:

Class:

- Click here for explanation of classification scheme.

Quality Rating:

Research Purpose:

To determine whether lower leg muscle mass and greater fat infiltration in the muscle were associated with poorer lower extremity performance (LEP) in a bi-racial sample of well-functioning older men and women.

Inclusion Criteria:

Participation in The Health, Aging and Body Composition (Health ABC) Study cohort
Reside in Pittsburgh, PA or Memphis, TN
White or black race
Age 70 to 79 during the recruitment period (March 1997 to July 1998).

Exclusion Criteria:

Age less than 70 years or greater than 79 years
Self-report of difficulty walking one fourth of a mile
Self-report of difficultly climbing 10 steps without resting
Difficulty performing basic activities of daily living
Use of a cane, walker, crutches or special equipment to ambulate
Active treatment or diagnosis of cancer within a three-year period prior to recruitment
Plans to move out of the study area(s) during a three-year period after recruitment
Missing data on muscle mass, lower extremity performance (LEP) or total body fat.

Description of Study Protocol:

Recruitment

Cohort participants were recruited from a random sample of Medicare beneficiaries residing in ZIP codes from the metropolitan areas surrounding Pittsburgh, PA and Memphis, TN.

Design

Cross-sectional analysis of baseline cohort data.

Blinding Used

Implied with measurements.

Statistical Analysis

Analyses were performed stratified by gender and race. Multivariate regression analysis was used to test the association of muscle area and attenuation with lower extremity performance (LEP). The nature of the relationship was first examined; a potential non-linear relationship or threshold for LEP was not observed. All analyses were adjusted for clinic site and age. A second set of models adjusted for total body fat. A final set of models adjusted for potential confounders known to be associated with muscle mass, muscle attenuation and LEP, including physical activity, health status, education and smoking status.

Data Collection Summary:

Timing of Measurements

All measurements were taken during a baseline examination after cohort entry.

Dependent Variables

Lower extremity performance (LEP) measured using two timed performance tests (six-meter walk and repeated chair stands).

Independent Variables

Muscle cross-sectional area by computed tomography scans at the mid-thigh
Muscle attenuation (indicative of fat infiltration) by computed tomography scans at the mid-thigh.

Control Variables

Clinic site
Age
Education
Body height
Total body fat
Physical activity
Health status
Smoking status.

Description of Actual Data Sample:

Initial N: 2,979 (1,442 men, 1,537 women)
Attrition (final N): 2,979
Age: 70 to 79 years at time of recruitment
Ethnicity: 1,752 white participants, 1,227 black participants
Other relevant demographics: 12.8% of white men and 9.4% of white women reported less than a high school education. 48.1% of black men and 37.5% of black women reported less than a high school education.
Anthropometrics:
- Black women had a higher mean BMI (29.6±5.8kg/m²) than white women (26.0±4.6kg/m²)
- Black women had significantly higher mean values for many body composition measurements than white women, including body weight (75.5±15.6kg vs. 66.2±12.2kg), total body fat (29.2±9.8kg vs. 24.9±7.7kg) and mid-thigh muscle mass (202±33cm² vs. 170±28cm²)
- Black women had lower mid-thigh muscle attenuation than white women (32.4±7.1 HU vs. 34.7±6.7 HU)
- Black men differed from white men in total body fat (20.0±7.2kg for black men vs. 21.6±6.7kg for white men) and mid-thigh muscle mass (277±49cm² for black men and 255±38cm² for white men)
Location: Pittsburgh, PA, US and Memphis, TN, US.

Summary of Results:

Key Findings

Mid-thigh muscle area and lower extremity performance (LP):
- In men, after adjustment for clinic site, age and body height, those with a lower muscle area had a poorer LP, which was maintained after adjustment for total body fat
- In women, the association between muscle area and LP was significant only after adjustment for total body fat was made
- Additional adjustment for lifestyle parameters, education and health status only slightly reduced the strength of the observations
- No interactions were observed between race and muscle area in men and women
- When the population was divided into tertiles of total body fat and mid-thigh muscle area, clear trends in LP across tertiles of total body fat (P=0.0001) and across tertiles of mid-thigh muscle area (P=0.0001) were observed. Persons in the highest tertile of total body fat had poorer LP with smaller mid-thigh muscle area than those with larger mid-thigh muscle area (P=0.007). Similar results were seen in persons in the medium tertile of total body fat (P=0.0008).

Regression Coefficients Increase in Mid-thigh Muscle Area in Relation to Lower Extremity Performance by Gender and Race

	White Men	Black Men	White Women	Black Women
Model 1	0.401±0.086*	0.381±0.090*	0.009±0.133	0.125±0.115
Model 2	0.658±0.090*	0.519±0.103*	0.547±0.145*	0.435±0.122*
Model 3	0.590±0.090*	0.457±0.101*	0.509±0.141*	0.427±0.118*

*P<0.01

Model 1 adjusted for clinic site, age, body height

Model 2 additionally adjusted for total body fat

Model 3 additionally adjusted for education, physical activity, health status and smoking.

Muscle attenuation and LP:
- Higher muscle attenuation (indication less fat infiltration into muscle tissue) was associated with better LP in men and women
- The associations were reduced, but remained significant after adjustment for total body fat as well as education, health status and lifestyle variables
- No interaction between race and muscle attenuation was observed in men or women
- Tertiles of mid-thigh muscle attenuation and total body fat showed clear trends for mid-thigh muscle attenuation (P=0.0001) and total body fat (P=0.0001). Among persons in the highest tertile of total body fat, those with low mid-thigh muscle attenuation had a poorer LP than those with high mid-thigh muscle attenuation (P=0.0005).

Regression Coefficients Increase in Mid-thigh Muscle Attenuation (HU) in Relation to LP by Gender and Race

	White Men	Black Men	White Women	Black Women
Model 1	0.392±0.061**	0.286±0.086**	0.419±0.065**	0.365±0.065**
Model 2	0.305±0.073**	0.346±0.102**	0.242±0.075**	0.232±0.073**
Model 3	0.283±0.072**	0.279±0.100**	0.204±0.074**	0.179±0.072*
Model 4	0.292±0.071**	0.244±0.100*	0.193±0.073**	0.159±0.072*

* P<0.05; **P<0.01

Model 1 adjusted for clinic site, age, body height

Model 2 additionally adjusted for total body fat

Model 3 additionally adjusted for education, physical activity, health status and smoking

Model 4 additionally adjusted for thigh muscle area.

Author Conclusion:

Lower leg muscle mass and lower muscle attenuation, indicative of greater fat infiltration in the muscle, are associated with poorer lower extremity performance (LEP) in older men and women
Observed associations were similar between blacks and whites and independent of overall body fatness suggesting an increase in muscle mass or muscle attenuation would be beneficial to LEP regardless of race and baseline level.

Funding Source:

Government:

Royal Netherlands Academy of Arts and Sciences; National Institute on Aging (NIH/USA)

Reviewer Comments:

The cohort in this study was made up of well-functioning older persons with no reported disabilities, which may have caused an underestimation of the observed associations.
Results may not be generalizable to all persons aged 70 to 79 years.

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.)	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.)	Yes
	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?	N/A
	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?		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?	Yes
	10.2.	Was the study free from apparent conflict of interest?	Yes