EAL

FNOA: Assessment of Overweight/Obesity (2012)

Citation:

Study Design:

Class:

- Click here for explanation of classification scheme.

Quality Rating:

Research Purpose:

To assess the association between limitations of activity and mortality among older, non-institutionalized white and African American women within BMI subgroups.

Inclusion Criteria:

Women
Age 65 years or older
Participant in any one of the National Health Interview Survey (NHIS) between 1986 and 1990
White or African American race
Complete information available on BMI levels, limitations of activity, education, health status and marital status.

Exclusion Criteria:

Age 65 years or less
Non-community dwelling
Race other than white or African American
Incomplete data on BMI levels, limitation of activity, education, health status and marital status.

Description of Study Protocol:

Recruitment

Data was used from annual National Health Interview Surveys conducted between 1986 and 1990. Data was analyzed on all white or African American survey participants for whom there was complete information on BMI levels, limitations of activity, education, health status and marital status.

Design

Prospective cohort study.

Statistical Analysis

Race-specific descriptive statistics were used to describe the study sample in each category of age, marital status, education, perceived health status and categories of health limitations
Multivariate survival analysis (Cox regression) was used to assess the relationship of limitation of activity to the risk of dying during the follow-up period within each group defined by race and BMI category
The risk ratios from the Cox regression models were adjusted for age, education, marital status and perceived health.

Data Collection Summary:

Timing of Measurements

Participants completed any one of the annual National Health Interview Surveys between 1986 and 1990. The National Center for Health Statistics linked the respondents with the Multiple Cause of Death Public Use Data File and matched deaths with the National Death Index to ascertain the vital status of all respondents through December 31st, 1991.

Dependent Variables

Health status (categorized into one of four groups based on survey responses:
- Unable to perform the major activity
- Limited in the amount or kind of major activity
- Limited, but not in the major activity
- Not limited.
The major activity for those aged 18 to 69 was working or keeping house and for those aged 70 years or older the major activity was the capacity for independence in personal and household care
Mortality.

Independent Variables

Body mass index.

Control Variables

Race
Age
Marital status
Years of education completed.

Description of Actual Data Sample:

Initial N: 24,612 women
Attrition (final N): 24,612 women
Age: 65 years or more
Ethnicity: 22,228 white women and 2,384 African American women
Other relevant demographics:
- 43.8% of white participants and 28.4% of African American participants were married
- 74.2% of white participants and 50.0% of African American participants had more than eight years of education
Location: National survey, conducted throughout the United States.

Summary of Results:

Key Findings

African American women were twice as likely as white women to report a poor heath status (18.2% vs. 9.4%, respectively)
African American women were more likely than white women to report some form of activity limitation (59% vs. 46%, respectively), with the percentage who were unable to perform the major activity almost twice as high for African American women vs. white women (18.5% vs. 9.8%, respectively)
Mortality rate (per 100) was highest among women with BMI levels below the 15th percentile (42% for white women and 36% for African American women)
For all BMI sub-groups, women who were unable to perform the major activity for her age category had higher mortality rates than women without activity limitations
The highest risk of dying (after adjusting for age, education, marital status and perceived health) was observed in women within each stratum of BMI who were unable to perform the major activity for age.

Risk of Death by Percentile of BMI and Limitations of Activity Among White Women

BMI Percentile^a	Deaths (%)	RR (95% CI)^b
Less than 15
I^c	205 (42.4)	2.8 (2.2 to 3.5)
II	176 (26.8)	1.7 (1.4 to 2.2)
III	91 (16.0)	1.2 (0.9 to 1.6)
IV	199 (12.3)	1.0 (Referent)
15 to 85
I	302 (23.9)	2.5 (2.1 to 2.9)
II	357 (14.8)	1.7 (1.4 to 1.9)
III	273 (9.5)	1.2 (1.1 to 1.4)
IV	612 (6.8)	1.0 (Referent)
More than 85
I	76 (17.4)	2.2 (1.6 to 3.1)
II	84 (11.1)	1.4 (1.0 to 1.9)
III	72 (10.1)	1.4 (1.0 to 1.9)
IV	94 (6.5)	1.0 (Referent)

^aBody Mass Index = kg/m²; BMI categorized by race specific percentiles.

^bRisk ratios and 95% confidence intervals are adjusted for age, education, marital status and perceived health.

^cActivity limitation categories are:

I Unable to perform major activity
II Limited in kind or amount of major activity
III Limited, but not in major activity
IV Not limited

Risk of Death by Percentile of BMI and Limitations of Activity Among African American Women

BMI Percentile^a	Deaths (%)	RR (95% CI)^b
Less than 15
I^c	32 (36.0)	1.4 (0.9 to 2.1)
II	23 (25.8)	0.6 (0.4 to 0.8)
III	6 (10.5)	0.5 (0.3 to 0.9)
IV	22 (18.7)	1.0 (Referent)
15 to 85
I	60 (21.7)	1.8 (1.5 to 2.3)
II	56 (16.8)	1.5 (1.2 to 1.8)
III	35 (11.4)	1.3 (1.0 to 1.6)
IV	50 (6.7)	1.0 (Referent)
More than 85
I	13 (17.1)	1.5 (0.9 to 2.5)
II	15 (14.6)	1.5 (1.0 to 2.5)
III	5 (7.6)	0.9 (0.5 to 1.6)
IV	10 (8.4)	1.0 (Referent)

^aBody Mass Index = kg/m²; BMI categorized by race specific percentiles.

^bRisk ratios and 95% confidence intervals are adjusted for age, education, marital status and perceived health.

^cActivity limitation categories are:
I Unable to perform major activity
II Limited in kind or amount of major activity
III Limited, but not in major activity
IV Not limited.

Author Conclusion:

Both high and low BMI are associated with functional impairment among community dwelling women older than 65 years, with the highest mortality rate among women with activity limitations who were in the lowest BMI category
Risk of death was found to be higher among women with activity limitations, regardless of BMI status
Associations between limitations in activity and mortality were generally similar along white and African American women within the BMI groups.

Funding Source:

Government:	Cardiovascular Health Branch, National Center for Chronic Disease Prevention and Health Promotion, Centers for Disease Control and Prevention
University/Hospital:	Prevention Center, School of Public Health, University of South Carolina

Reviewer Comments:

The study relied on self-reported height and weight, from which BMI was calculated as well as self-reported perceived health and limitation in activity
The analysis did not control for potential confounding factors such as physical activity or chronic illness
The length of time for follow-up was variable (one to five years) based on when the participant completed the initial survey; therefore, the outcome variable of mortality would be seen in higher prevalence for those women completing a survey during one of the earlier years (having five years of follow-up) than the later years (having one to two years of follow-up). Nothing is known about a potential change in health status or activity level during the years between the initial survey and the time when mortality data was collected.
It is unknown how long the women were limited in activity or perceived poor health status prior to survey or, ultimately, to mortality
BMI seemed to play a far lesser role than activity limitation in mortality rate.

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?		???
	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?	???
	3.3.	Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.)	No
	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?	???
	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?		N/A
	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?	N/A
	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?		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?	N/A
	7.3.	Was the period of follow-up long enough for important outcome(s) to occur?	???
	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?	No
	7.6.	Were other factors accounted for (measured) that could affect outcomes?	No
	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?	No
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