FNOA: Assessment of Overweight/Obesity (2012)

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

To analyze the association between body mass index and both all-cause and cause-specific mortality among men from the Physician's Health Study enrollment cohort.

Inclusion Criteria:
  • Male gender
  • Physician within the United States
  • Age 40 to 84 years
  • Completed an initial enrollment questionnaire for the Physician's Health Study in 1982 to 1983.
Exclusion Criteria:
  • History of previous myocardial infarction, angina pectoris, stroke, transient ischemic attack, cancer, liver disease or renal disease reported on baseline questionnaire
  • Did not provide information on height and weight.
Description of Study Protocol:

Recruitment

Letters of invitation, informed consent and baseline questionnaires were mailed to 261,248 eligible US male physicians aged 40 to 84 years in 1982 to 1983.

Design

Prospective cohort study based on Physician's Health Study enrollment cohort.

Blinding Used

Implied with measurements.

Statistical Analysis

Means and proportions of baseline risk factors for six BMI categories were calculated. Relative risks and 95% CI for the occurrence of fatal events associated with these BMI categories were calculated using proportional hazard regression models. Test for linear and deviation from linear trend was performed. Multivariate analysis that controlled for age, cigarette smoking, alcohol consumption and physical activity was performed.

Data Collection Summary:

Timing of Measurements

All measurements (excluding report of death) were taken from a baseline questionnaire mailed to eligible physicians at the time of study enrollment.  The National Death Index was used to identify study members who had died through a specified period of time (December 31, 1988). Trained nosologists classified the cause of death.

Dependent Variables

  • All-cause mortality (National Death Index)
  • Cause-specific mortality (National Death Index).

Independent Variables

Body mass index (calculated from self-reported height and weight).

Control Variables

  • Age
  • Smoking
  • Alcohol intake
  • Physical activity.
Description of Actual Data Sample:
  • Initial N: 85,078 (all men)
  • Attrition (final N): 85,078
  • Age: 40 to 84 years
  • Other relevant demographics: All physicians, limiting confounding by educational attainment, socioeconomic status and access to healthcare
  • Anthropometrics: Six BMI categories were constructed. The number of participants in each category is listed below:
BMI Category (kg/m2) N
Less than 20 1,641
20.0 to 22.4 14,390
22.5 to 24.9 31,380
25.0 to 27.4 24,550
27.5 to 29.9 7,995
30 or more 5,122
  • Location: United States.

 

Summary of Results:

Key Findings

  • BMI and all-cause mortality:
    • Age-adjusted analyses yielded a well-fitted U-shaped curve (P<0.001 for curvilinear trend)
    • Relative risks were lowest in the intermediate BMI quintiles
    • Adjusting for smoking habit, alcohol intake and physical activity resulted in a visually less pronounced U-shaped curve
    • When the analysis was restricted to men who had never smoked, a linear association was observed showing no excess risk among leanest men (P<0.001 for linear trend; P>0.1 for curvilinear trend)
    • When deaths during the first two years of observation were excluded, the association was strengthened with mortality in the highest BMI category almost double that of the lowest (P<0.001 for linear trend)
  • All-cause mortality according to BMI categories:
  Less than 20kg/m2 20.0 to 22.4kg/m2 22.5 to 24.9kg/m2 25.0 to 27.4kg/m2 27.5 to 29.9kg/m2 30kg/m2 or More
All men 1,641 14,390 31,380 24,550 7,995 5,122
Number of deaths 97 466 935 823 297 238
Person-years of follow-up 8,771 78,910 172,265 134,368 43,668 27,877
Age-adjusted RR 1.77 1.12 1.00 1.10 1.25 1.73
Multivariate RR (95% CI) 1.57 (1.26 to 1.95) 1.07 (0.95 to 1.20) 1.00 (ref) 1.09 (0.99 to 1.20) 1.19 (1.04 to 1.36) 1.61 (1.39 to 1.86)
  • BMI and disease-specific mortality:
    • Cardiovascular disease:
      • When cardiovascular disease deaths were analyzed separately for BMI, the age-adjusted results fit a U-shaped curve (P<0.05 for curvilinear trend)
      • Restricting this analysis to never smokers resulted in a linear trend (P<0.001 for linear trend; P>0.1 for deviation from linearity)
  • Cancer:
    • The association between BMI and cancer deaths followed a U-shaped curve (P=0.05 for curvilinear trend)
    • Restricting the analysis to never smokers resulted in less pronounced curvature in the association (P>0.1 for curvilinear trend)
  • Other:
    • No associations or trends were observed between body mass index and non-cardiovascular disease, non-cancer deaths in the multivariate model
    • When analysis was performed investigating whether frequency of vigorous exercise at baseline modified the association between BMI and mortality, increasing all-cause and cardiovascular mortality were observed with increasing BMI among both physically active and sedentary men.
Author Conclusion:
  • All-cause and cardiovascular mortality was directly related to BMI among middle-aged and elderly men
  • Advancing age did not attenuate the increased risk of death associated with obesity
  • Lean men (BMI less than 20) did not have excess mortality, regardless of age.
Funding Source:
University/Hospital: National Institutes of Health
Reviewer Comments:
  • Height and weight were self-reported
  • Sample homogeneous in nature (all physicians); associations between BMI and mortality might be applicable to US men as a whole
  • No information on weight change over time.
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? No
  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? No
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.) 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%.) 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? 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? 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