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DLM: BMI (2001)

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

Examine indicators of obesity in relation to mortality among men, including how the relations depend on age.

Inclusion Criteria:

Selected for inclusion in the Health Professionals Follow-Up Study:

  • Male health professionals
  • Age 40 to 75 years in 1986.
Exclusion Criteria:

From data collected from 1986 questionnaire:

  • Myocardial infarction (MI)
  • Coronary artery bypass graft (CABG), angioplasty
  • Stroke, transient ischemic attack (TIA)
  • Peripheral venous thrombosis
  • Intermittent claudication
  • Pulmonary embolus
  • Paroxysmal atrial tachycardia
  • Heart rhythm disturbances
  • Cancer
  • Chronic Renal Failure (CRF)
  • Chronic pulmonary disease
  • No body weight
  • Body Mass Index (BMI) less than 15kg per m2 or more than 50kg per m2.
Description of Study Protocol:

Recruitment

Male health professionals 40 to 75 years of age (dentists, veterinarians, pharmacists, optometrist, osteopaths, podiatrists).

Study Design 

  • Prospective longitudinal study begun in 1986
  • Completed dietary and lifestyle questionnaire and biannual questionnaires during 10 years of follow-up.

Statistical Analysis

  • Men grouped into:
    • Six categories of BMI
    • Quintiles of waist circumference, hip circumference and waist to hip ratio.
  • Calculated relative risks (RR) adjusted for age using the Mantel-Haenszel method
  • Estimated RR as odds ratios using multiple logistic regression models.

 

Data Collection Summary:

Dependent Variables

All cause mortality and death from CVD.

Independent Variables

  • BMI, calculated from height and weight in 1986 and at age 21
  • Waist circumference, self-measured using pictoral instructions
  • Waist-to-hip ratio.

Control Variables

  • Age
  • Smoking
  • Family history of heart attack or colon cancer before age 60
  • Profession
  • Marital status
  • Alcohol consumption
  • Consumption of antioxidant supplements and dietary fiber.
Description of Actual Data Sample:
  • Number of subjects: 39,766 men
  • Age: 50 to 85 years
  • Ethnicity: Not reported
  • Demographic data: Not described in this report
  • Anthropometric data: Age-standardized BMI range was 20.0 to 32.7kg per m2
  • Location: United States.
Summary of Results:
  • During 10 years of follow-up, 1,972 deaths were documented
  • After exclusion of men with substantial recent weight loss and deaths occurring during the first four years of follow-up, overall and CVD mortality among men less than 65 years of age, ú linearly with higher BMI. However, there was no relationship for overall mortality, or mortality from CVD in those older than 65 years of age.
  • BMI Multivariate RR for overall mortality (P for trend <0.001)
    • 1.0 for those with BMI less than 23kg per m2
    • 1.21 for a BMI of 23 to 24.9kg per m2
    • 1.19 for a BMI of 25 to 26.9kg per m2
    • 1.39 for a BMI of 27 to 29.9kg per m2 
    • 1.97 for a BMI more than 30kg per m2
  • Multivariate RR for CVD mortality less than 65 years of age (P for trend <0.001)
    • 1.0 for those with BMI less than 23kg per m2
    • 0.72 for those with BMI 23 to 24.9kg per m2
    • 1.76 for those with BMI 25 to 26.9kg per m2
    • 2.26 for those with BMI 27 to 29.9kg per m2 
    • 3.92 for those with BMI more than 30kg per m2 
  • Waist circumference categories in inches: Less than 34.5; 34.5 to 36.2; 36.3 to 37.9; 38 to 40.2; more than 40.3
    • Less than 65 years of age: RR 1.54 (95% CI, 0.79, 2.99), 0.74 (95% CI, 0.32, 1.73), 1.78 (95% CI, 0.93, 3.41), 2.94 (95% CI, 1.56, 5.52) (P for trend <0.001)
    • More than 65 years of age: RR 0.72 (95% CI, 0.27, 1.96) 2.37 (95% CI, 1.03, 5.45) 1.98 (95% CI, 0.88, 4.48) 3.50 (95% CI, 1.60, 7.66) (P for trend <0.001)
  • Among men less than 65 years of age, the lowest risk of overall mortality was seen for BMI less than 23kg per m2 
  • Among men more than 65 years of age, there were no significant relations between BMI and all-cause morality or morality from CVD. Waist circumference strongly predicted risk of death from CVD among the older men. Thus, in older men, guidelines based on waist circumference rather than weight alone may be more useful in predicting CVD mortality.
Author Conclusion:
  • In men less than 65 years of age, a direct relation between BMI and overall mortality was observed
  • In men more than 65 years of age, there was no relationship between BMI and risk of overall mortality. However, in this group, waist circumference was related directly to risk of death from CVD or CHD.
  • The authors concluded that excessive body fat contributes to mortality at all ages, but for older men, guidelines based on waist circumference may be more useful than guidelines based on weight.
Funding Source:
Government: National Institutes of Health (NIH), Korea Research Foundation
Reviewer Comments:

The limitation of this study was self-reported body weight, height, waist circumference and hip circumference.

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) 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? No
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) N/A
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? N/A
  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? N/A
  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? 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? N/A
  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? N/A
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? N/A
  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