FNOA: Assessment of Overweight/Obesity (2012)

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

To compare the risk nadir BMIs for Japanese to the BMIs for whites as determined by similar studies and to compare the risk nadir BMIs for Japanese to the official BMI guidelines (WHO and Japan Society for the Study of Obesity). 

Inclusion Criteria:
  • A total of 38 communities out of 85 in Ibaraki prefecture, Japan, were adopted for use in this study
  • Subjects were enrolled if they had undergone health checkups conducted by the Ibaraki Health Service Association in 1993.
Exclusion Criteria:
  • At baseline health checkups, 490 men and 1,606 women were excluded because of incomplete data
  • Two men and four women were excluded because they moved out of their community before their health checkups
  • An additional 862 men and 1,256 women were excluded when they died or moved out during the first three years of follow-up.
Description of Study Protocol:

Recruitment

38 out of 85 communities in Ibaraki Japan were used in this study. Subjects were enrolled if they had undergone health checkups conducted by the Ibaraki Health Service Association in 1993. Recruitment methods were not described. 

Design

Prospective cohort study. 

Blinding Used

Implied with measurements. 

Statistical Analysis:

  • Participants were classified into seven categories with regard to their BMI: Less than 18.5, 18.5 to 30.9, 21.0 to 22.9, 23.0 to 24.9, 25.0 to 26.9, 27.0 to 29.9 or 30.0kg/m2
  • Risk ratios for all-cause mortality relative to BMI categories were calculated with a reference of 21.0 to 22.9kg/m2 using a Cox proportional hazards regression model
  • Covariates included age in years, alcohol intake (66g per day or more or not) and smoking status (never smoked, former smoker, current smoker of less than 20 cigarettes per day or current smoker of 20 or more cigarettes per day)
  • Age and gender-specific risk nadir BMIs were determined by a computer according to the model-based approach with transformed BMI. The delta method was used to establish their confidence intervals (CIs).
  • Cox proportional hazards models were calculated, which included the quadratic term of 1 per BMI and adjusted values (age, alcohol intake and smoking status), thus treating BMI as a continuous variable
  • All statistical analyses were conducted using SAS, version 9.1.

 

Data Collection Summary:

Timing of Measurements

Baseline measurements made in 1993 and subjects were followed through 2003.

Dependent Variables

  • Mortality risk
  • Mortality surveillance were performed by reviewing certificates of residence provided by local government officials.

Independent Variables

  • Height was measured in stocking feet and weight was measured in light clothing
  • BMI was calculated as weight (kg) divided by the square of the height (m)
  • Blood pressure was measured at baseline on the right arm of a seated participant by a trained observer using a standard mercury sphygmomanometer.Blood was drawn into two polythylene tubes.
  • Blood glucose was measured at baseline using a glucose oxidase electrode with a GA1140 device
  • Serum total cholesterol and serum triglyceride levels were measured at baseline with an enzyme method using an RX-30 device
  • High-density lipoprotein cholesterol was measured at baseline with a phosphotungstic acid magnesium method using an MTP-32 device.

Control Variables

  • Covariates included age in years, alcohol intake (66g or more per day or not) and smoking status (never smoked, former smoker, current smoker of less than 20 cigarettes per day or current smoker of 20 or more cigarettes per day)
  • A baseline interview was also conducted to ascertain treatment of hypertension, treatment of diabetes, treatment of dyslipidemia, alcohol intake (never, sometimes, less than 66g per day or 66 or more g per day) and smoking status (never smoked, former smoker or current smoker) for current smokers the number of cigarettes per day.
Description of Actual Data Sample:
  • Initial N: 98,196 subjects (33,414 men and 64,782 women)
  • Attrition (final N): 93,976 subjects (32,060 men and 61,916 women)
  • Age: 40 to 79 years
  • Ethnicity: Japanese
  • Anthropometrics: Groups were similar
  • Location: Ibaraki prefecture, Japan.
Summary of Results:

Key Findings

  • There were 3,930 total deaths among the 32,060 men and 3,164 total deaths among the 61,916 women
  • The standard mortality ratio of all-cause mortality among the study participants was 95 for men (95% confidence interval: 86 to 103) and 100 for women (95% confidence interval:  89 to 110) compared with the total Japanese population in 2000
  • For both age and both gender categories, the relationship between all-cause mortality risk and BMI categories are illustrated as U-shaped curves
  • The risk nadir BMIs for men in the age groups of 40 to 59 and 60 to 79 years were 23.4 and 25.3kg/m2, respectively
  • Similarly, in women, the risk nadir BMIs were 21.6 and 23.4kg/m2, respectively.
 

Age Group 40-59 (Men)

Age Group 60-79 (Men)

Age Group 40-59 (Women)

Age Group 60-79 (Women)

Age and gender-specific BMIs in terms of lowest mortality

23.4kg/m2

95% CI: 22.0-24.9

P=0.0018

25.3kg/m2

95% CI: 23.1-27.8

P<0.0001

21.6kg/m2

95% CI: 20.2-23.0

P<0.0001

23.4kg/m2

95% CI: 22.5-24.2

P<0.0001

 

 

Author Conclusion:

The risk nadir BMI for people aged 60 to 79 years was higher than for people aged 40 to 59 years among the general Japanese population, and this result was similar to the study for whites. The age-dependent risk nadir BMI differed from the official guidelines criteria (WHO and Japan Society for the Study of Obesity).

Funding Source:
Government: Local government in Ibaraki, Japan
Reviewer Comments:
  • Study strengths:
    • The cohort in this study was large and age and gender stratification analysis was possible 
    • All blood samples were measured by the same device and quality control program
  • Study limitations:
    • The data using adjusted variables (alcohol intake and smoking status) were based on interview questionnaires and there is no information on the validity of the questions
    • It is difficult to compare the risk nadir BMIs for men and women because there is a difference in the rate of smoking between men and women in the study
    • The subjects of the study were participants in a health checkup for community residents that had a response rate of 40%. This potential selection bias may be small because the rate of all-cause mortality did not differ between the study subjects and the total Japanese population.
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? ???
  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? ???
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? 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? 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? 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)? No
  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