EAL

FNOA: Assessment of Overweight/Obesity (2012)

Citation:

Study Design:

Class:

- Click here for explanation of classification scheme.

Quality Rating:

Research Purpose:

To evaluate the joint and relative associations of body mass index (BMI), waist circumference, and waist-hip ratio with multiple disease end-points.

Inclusion Criteria:

Participants in the Iowa Women's Health Study
Ages 55-69 at baseline
Hold a valid Iowa driver's license in 1985.

Exclusion Criteria:

Those who were premenopausal
Those who reported a baseline history of cancer, heart disease, or diabetes
Those who had missing data on BMI and waist-hip ratio.

Description of Study Protocol:

Recruitment

Participants were randomly selected women who owned a valid Iowa driver's license. They were invited to participate in a mailed questionnaire.

Design

Prospective cohort study

A baseline questionnaire included questions on educational level, smoking status, alcohol intake during the past year, hormone replacement therapy status, and reproductive history. Participants were asked three questions about whether they participated in leisure-time exercise (including frequency and intensity). A food frequency questionnaire was used to assess dietary intake. Women were asked if they had ever had any form of cancer, excluding skin cancer. Prevalence of heart disease was ascertained through self-reports of physician-diagnosed MI, angina, or other heart disease. Prevalence of hypertension and diabetes were also assessed via questionnaire. Prevalence of hip fracture was self-reported.

Enclosed with the questionnaire were a paper tape measure and written instructions on how to have a friend measure waist circumference. Current height and weight were self-reported and BMI was derived from that information.

Mailed follow-ups took place in 1987, 1989, 1992 and 1997. Names, social security numbers, and date of birth (DOB) were linked with the National Death Index and State Health Index for Iowa to gather information on deaths. Cancer Incidence was identified by computer linkage with the State Health Registry of Iowa. Other incident disease end-points were obtained during follow-up surveys as the first positive self-report of a physician diagnosis.

Blinding used

Not applicable

Intervention

Not applicable

Statistical Analysis

Women were categorized according to quintiles (or tertiles when there were few end-points) of the baseline anthropometric variables. Age-adjusted relative risks (and their 95% CI and P values) were calculated by Mantel-Haenszel methods. Multivariate adjusted risk ratios (RR) (and their 95% CI's were computed by proportional hazards regression. Multivariate adjusted RR were computed for BMI, waist-hip ratio, and waist circumference separately. BMI and waist-hip ratio were computed simultaneously. Age-adjusted odds ratios for pooled end-points were computed using unconditional logistic regression.

Data Collection Summary:

Timing of Measurements

Participants were recruited and baseline information gathered in beginning in January, 1986. Follow-up took place in 1987, 1989, 1992 and 1997.

Dependent Variables

Incidence of death as obtained by the Iowa State Health Registry and the National Death Index
Incidence of cancer as obtained by the Iowa State Health Registry of Iowa
Incidence of high blood pressure as self-reported
Incidence of heart disease as self-reported of a physician diagnosis of myocardial infarction, angina, or other heart disease
Incidence of diabetes as self-reported
Incidence of hip fracture as self-reported.

Independent Variables

BMI as measured by self-report of weight and height with BMI derived from that information
Waist circumference as measured at 2.5cm above the umbilicus
Waist-hip ratio (waist circumference as measured above, hip circumference as measured at the maximal protrusion).

Control Variables

Age

Description of Actual Data Sample:

Initial N: 31,702 women from the Iowa Women's Health Study who met the inclusion criteria
Attrition (final N): Participants were lost to follow-up at every follow-up as follows:
- 1987 (9%)
- 1989 (10%)
- 1992 (17%)
- 1997 (21%)
- 2,476 participants died over the course of the study. The exact number of those enrolled vs. those who were lost to follow-up was not specified.
Age: 55-69 years at baseline
Ethnicity: Not specified
Other relevant demographics: Data on educational level was obtained and within five BMI quintiles, the education level of participants varied
Anthropometrics: Participants were broken down into five quintiles for BMI and waist-hip ratio
Location: Iowa.

Summary of Results:

Key Findings

After adjustment for other risk factors, women with general obesity (defined by BMI and waist circumference) were not at increased risk for death. There was a graded risk of mortality across quintiles of waist-hip ratio. The highest mortality stratum was that with the lowest BMI and highest waist-hip ratio.
BMI, waist-hip ratio, and waist circumference were associated positively with CHD-related mortality. A higher BMI and waist-hip ratio were associated with greater CHD-related mortality among the total sample. The waist-hip ratio was associated positively, BMI was associated negatively, and waist circumference was not associated with other CVD-related deaths.
Body mass index, waist-hip ratio, and waist circumference were not significantly associated with cancer-related mortality after adjustment for other risk factors
Cancer incidence tended to be associated positively with all three anthropometric variables. General obesity appeared to be more strongly associated with breast cancer, colon cancer, and uterine cancer.
Body mass index, waist-hip ratio, and waist circumference were strong risk factors for self-reported diabetes. All three anthropometric variables were associated positively with incidence of self-reported high blood pressure.
Body mass index was associated inversely with occurrence of hip fracture, whereas waist-hip ratio was associated slightly positively and waist circumference was not at all associated with hip fracture.

Association of Anthropometric Variable with Mortality From All Cause, Coronary Heart Disease, Other Cardiovascular diseases, and Cancer

Mortality End-Point	n	Age-Adjusted Models Quintiles					RR (95% CI) for Multi-variable-Adjusted Models (Quintile 5 vs. 1)
		1	2	3	4	5	Separate	Combined
All Cause
BMI	n	716	701	705	739	877	1.2 (1.2-1.5)	1.3 (1.2-1.4)
Waist-hip ratio	n	367	411	492	555	651	1.2 (1.1-1.4)	1.4 (1.2-1.6)
Waist circumference	n	447	473	439	473	644	1.2 (1.0-1.3)
Coronary Heart Disease
BMI	n	74	73	87	81	123	(1.20-2.3)	1.3 (0.9-1.9)
Waist-hip ratio	n	45	62	78	118	135	1.9 (1.3-2.9)	1.8 (1.2-2.7)
Waist circumference	n	47	75	80	96	140	2.2 (1.5-3.2)
Other cardiovascular diseases
BMI	n	77	62	48	69	70	0.72 (0.5-1.1)	0.6 (0.4-0.9)
Waist-hip ratio	n	45	59	62	66	94	1.4 (0.9-2.1)	1.7 (1.1-2.7)
Waist circumference	n	48	74	54	66	84	1.2 (0.8-1.8)
Cancer
BMI	n	269	234	210	199	244	1.0 (0.8-1.2)	0.92 (0.7-1.1)
Waist-hip ratio	n	187	209	247	242	271	1.2 (0.9-1.4)	1.2 (0.98-1.5)
Waist circumference	n	222	236	200	218	280	1.2 (0.96-1.4)

Association of Anthropometric Variables with Incidence of Self-Reported Diabetes, High Blood Pressure, and Hip Fracture

Mortality End-Point	Variable	Quintile					RR (95% CI) for Multi-variable-Adjusted Models (Quintile 5 vs. 1)
		1	2	3	4	5	Separate	Combined
Diabetes
BMI	n	63	122	1,814	407	802	13.1 (9.8-17.3)	6.5 (4.9-8.8)
Waist-hip ratio	n	73	137	214	411	743	13.9 (8.6-14.7)	5.1 (3.9-6.8)
Waist circumference	n	55	94	190	402	837	15.9 (11.7-21.7)
High Blood Pressure
BMI	n	709	764	817	906	881	2.3 (2.0-25)	1.9 (1.7-2.2)
Waist-hip ratio	n	734	806	818	844	875	1.9 (1.8-2.2)	1.5 (1.3-1.7)
Waist circumference	n	711	737	824	909	896	2.4 (2.1-2.6)
Hip Fracture
BMI	n	135	87	89	86	87	0.59 (0.4-0.8)	0.49 (0.4-0.7)
Waist-hip ratio	n	80	91	107	100	106	1.1 (0.8-1.6)	1.6 (1.1-2.2)
Waist circumference	n	102	92	98	93	99	0.87 (0.6-1.2)

Author Conclusion:

Waist-hip circumference helps identify women at increased risk of death and several other important illnesses beyond BMI and waist circumference.

Funding Source:

Government:

National Cancer Institute

University/Hospital:

University of Minnesota

Not-for-profit

Mayo Foundation

Other non-profit:

Reviewer Comments:

This reviewer is not clear on the number of participants that were lost to attrition
Self-reporting of height and weight and self-measurement of waist and hip measurement could have resulted in error
It is unclear to this reviewer if follow-ups over the 10-year period included data about lifestyle (such as diet and exercise, medication and supplement use). These factors could affect incidence of mortality and disease.

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)	N/A
	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?		No
	4.1.	Were follow-up methods described and the same for all groups?	No
	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%.)	No
	4.3.	Were all enrolled subjects/patients (in the original sample) accounted for?	No
	4.4.	Were reasons for withdrawals similar across groups?	???
	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?		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?	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?	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?	???
	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