DLM: BMI (2001)

Citation:
 
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:

To compare waist-hip ratio (WHR) and waist circumference in determining risk of CHD in women.

Inclusion Criteria:
  • United States, female registered nurses participating in the Nurses' Health Study (NHS)
  • Nurses completed a questionnaire and follow-up in June 1994
  • Women aged 40 to 65 years who provided waist and hip circumferences and were free of prior CHD, stroke or cancer in 1986.
Exclusion Criteria:
  • From 1986 questionnaire data
  • No prior history of CHD, stroke or cancer
  • Definition of CHD:
    • Myocardial infarction (MI) classified my medical record review
    • WHO criteria for symptoms
    • Either EKG changes or ­cardiac enzymes
  • Cause of death from death records.
Description of Study Protocol:
  • The Nurses' Health Study (NHS) cohort was formed in 1976 when121,701 female registered nurses, aged 30 to 55 years and living in 11 US states, returned a mailed questionnaire. These women have answered questionnaires every two years, reporting information about exposures, risk factors and health outcomes, including the diagnosis of MI. All covariates for these analyses were obtained from the 1986 questionnaire with the exception of height (collected in 1976), aspirin intake (collected in 1984), family history of MI (collected in 1976 and 1980) and oral contraceptive use (collected biennially from 1976 to 1984). In 1986, women were instructed to measure their waist at the level of the umbilicus and their hips at the largest circumference with a tape measure while standing relaxed and to report values to the nearest quarter inch (reported herein in centimeters [inches]).
  • Fatal CHD was considered confirmed if hospital or autopsy recordsconfirmed fatal MI or the death certificate listed CHD as the primary cause of death and available evidence from next of kin, hospital records or prior participant report indicated a previous diagnosis of CHD. Incidence rates were calculated by dividing the number of new cases by the number of person-years of follow-up for each category. Rates were age-adjusted in five-year age intervals.
  • Cox proportional hazards models were used to estimate the relative risk of CHD outcomes across each anthropometric category. Models were fit controlling simultaneously for age and available relevant confounders. Pearson correlations among the anthropometric variables were calculated. Person-years of follow-up were calculated as the time from completion of the 1986 questionnaire to June 1994 or the diagnosis of an end point.
Data Collection Summary:
  • Data collected: 
    • 1986: Waist and hip measurements
    • Other years: Aspirin use, family history of MI, oral contraceptive use
  • Outcome measures: CHD (nonfatal MI or CHD death).
Description of Actual Data Sample:
  • 44,702 women aged 40 to 65 years of age had complete data
  • 320 CHD events (0.7%) over the eight years
    • 251 MI (0.56%)
    • 69 CHD deaths (0.15%).
Summary of Results:
  • After adjusting for BMI and other cardiac risk factors, women with a WHR of more than 0.88 had an RR of 3.25 (95% CI, 1.78 to 5.95) for CHD compared with women with a WHR of less than 0.72. A waist circumference more than 96.5cm (38 inches) was associated with an RR or 3.06 ((95% CI, 1.54 to 6.10).
  • The WHR and waist circumference were independently strongly associated with­ risk of CHD also among women with a BMI of  less than 25kg per m2. After adjustment for reported hypertension, diabetes and cholesterol level, a WHR of more than 0.76 or waist circumference of more than 76.2cm (30 inches) was associated with more than a two-fold ­ risk of CHD. The WHR and waist circumference are independently associated with risk of CHD in women.

Multivariate Relative Risks (95% confidence intervals) for Coronary Heart Disease, According to Quintiles of Waist-Hip Ratio and Waist Circumference

Waist-Hip Ratio Quintile

Model  1*

1 (0.37-<0.73)

2 (0.73-<0.76)

3 (0.76-<0.79)

4 (0.79-<0.83)

5 (0.83-<1.90)

P-trend

Model  1*

1.00 (Referent)

1.34 (0.78-2.72)

1.63 (0.97-2.71)

2.04 (1.24-3.34)

2.58 (1.58-4.22)

<0.001

Model 2

1.00 (Referent)

1.38 (0.80-2.38)

1.74 (1.04-2.90)

2.25 (1.38-3.67)

3.09 (1.93-4.96)

<0.001

Waist circumference quintile (cm)

 

1 (38.1-<69.8)

2 (69.8-<74.2)

3 (74.2-<79.2)

4 (79.2-<86.3)

5 (86.3-<139.7)

P-trend

Model  1*

1.00 (Referent)

1.27 (0.74-2.18)

2.08 (1.23-3.54)

2.31 (1.31-4.06)

2.44 (1.34-4.44)

0.007

Model 2

1.00 (Referent)

1.19 (0.71-2.00)

1.96 (1.22-3.17)

2.27 (1.42-3.64)

2.69 (1.72-4.22)

<0.001

*Model 1 is adjusted for BMI (<21,21-<23, 23-,25, 25-<27,27-<29,29-,31, ≥31 kg per m2), age, age2, smoking (status and amount), parental history of MI, alcohol consumption (g per day), physical activity (metabolic equivalent units), menopausal status, hormone replacement therapy, oral contraceptive use, aspirin intake, saturated fat intake (g per day) and antioxidant score.

Model 2 is adjusted for all of the variable in Model 1 except BMI.

 

Author Conclusion:
  • Subjects did their own waist and hip measurements which is a limitation of the study
  • Measures of regional fat distribution are independently associated with risk of CHD in women. In this cohort, both WHR and waist circumference were significantly associated with increased risk of CHD, even after controlling for BMI. In analyses stratified by BMI, higher WHR or waist circumference tertile was associated with higher risk of CHD, regardless of BMI tertile. After controlling for BMI and other cardiac risk factors, women with a WHR of 0.76 or greater were more than twice as likely to develop CHD during follow-up, while women with a WHR higher than 0.88 were more than three times as likely to develop CHD. Women in the highest quintile of WHR or waist circumference were nearly 2.5 times more likely to develop CHD than women in the lowest quintile. More than a two-fold residual risk of CHD was seen among women in the highest WHR category (≥0.88), even after controlling for these biological mediators.
  • Follow-up rates in this large prospective cohort are high, end points have been carefully documented and reliability of self-reported risk factor information has been high
  • WHR was associated with increased risk even among heavier women.
Funding Source:
Government: NIH
Reviewer Comments:
  • This is very well written paper. This is an observational study. Controlled clinical trials are required in different ethnic and different population. Dietary intake data with reference to the incidence rate of CHD is missing in the current paper. It was very clear that abdominal obesity increases CHD risk in women. Clinical recommendations are required to reduce the risk of CHD in women who have higher BMI and WHR.
  • Post-menopausal women may have higher risk of CHD. Hence, further studies need to focus and to differentiate pre- and post-menopausal women and abdominal obesity in relation CHD incidence and CHD risk. Identifying a CHD risk score at an early condition is necessary in women with higher BMI and WHR.

 

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? N/A
  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? N/A
  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? N/A
  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? Yes
  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? N/A
  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.) ???
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? N/A
  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? Yes
  6.6. Were extra or unplanned treatments described? Yes
  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? Yes
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)? Yes
  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? Yes
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