DLM: Omega-3 Fatty Acids (2009-2010)

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

To analyze the relationship between fish consumption and all-cause and cause-specific mortality in the Japanese population living in Japan.

Inclusion Criteria:
  • Participants in the 1980 National Survey on Circulatory Disorders
  • 30 years of age or older
  • Living in one of the 300 randomly selected health districts throughout Japan. 
Exclusion Criteria:
  • Past history of coronary disease, stroke, cancer or significant co-morbidities such as renal insufficiency
  • Some missing information at the baseline survey
  • Lost to follow-up.
Description of Study Protocol:

Recruitment

  • Information about the method of recruitment is not given in this study
  • The article reporting the original survey is referenced.

Design

  • Participants in the 1980 National Survey on Circulatory Disorders were surveyed and examined at baseline by public health centers and the following data were collected or measured:
    • Blood pressure
    • Height
    • Weight
    • Body mass index (BMI)
    • Lifestyle survey
      • Food-frequency questionnaire. Fish consumption was queried using five categories: two or more times per day, approximately one time per day, approximately one time per two days, approximately one to two times per week and less than once per week.
      • Smoking habit
      • Drinking habit
      • Medical histories.
    • Non-fasting blood samples
      • Total cholesterol
      • Glucose.
  • Participants were followed up for 19 years and the underlying causes of death were coded according to the ninth International Classification of Disease for the National Vital Statistics
  • Participants were grouped according to their fish consumption and baseline characteristics, and mortality data were analyzed.

Statistical Analysis

  • Chi-square test
  • Cox's proportional hazard model
  • For multivariate analyses, age, sex, cigarette smoking, alcohol intake, hypertension, BMI and diabetes were entered as covariates.

 

Data Collection Summary:

Timing of Measurements

Measurements were taken at baseline only.

Dependent Variables

  • All-cause mortality
  • Cause-specific mortality
    • Stroke death
    • Cerebral hemorrhage death
    • Cerebral infarction death
    • Coronary heart disease death.

Independent Variable

Fish consumption.

 

 

Description of Actual Data Sample:

Initial N

10,546 participants.

Attrition (final N)

8,879 (3,945 men; 4,934 women).

Mean Age

  • Participants eating two or more servings of fish per day, 53.4 years
  • Participants eating one serving of fish per day, 50.8 years
  • Participants eating one serving of fish every two days, 49.4 years
  • Participants eating one to two servings of fish every week, 50.3 years
  • Participants seldom eating fish, 53 years.

Ethnicity

Japanese.

Anthropometrics

BMI was approximately the same for all participants.

Location

Living in a randomly selected health district in Japan.

Summary of Results:

 

Variables

2+/day

1/day

1/2 days 1-2/week Seldom

Trend P

Total person-years 9,738 50,488 50,066 39,149 4,433  

All-cause death, N

Mortality per 1,000 person-years        

RR (95% CI)

138

14.2

0.99 (0.77-1.27)

584

11.6

1.03 (0.88-1.20)

496

9.9

0.98 (0.85-1.12)

450

11.5

1

77

17.4

1.12 (0.87-1.44)

Total=1,745

 

P=0.94

Stroke death, N

Mortality per 1,000 person-years    

RR (95% CI)

26

2.7

1.26 (0.70-2.29)

101

2

1.20 (0.82-1.75)

80

1.6

1.09 (0.78-1.53)

67

1.7

1

14

3.2

1.34 (0.73-2.44)

Total=288

 

P=0.52

Cerebral hemorrhage death, N

Mortality per 1,000 person-years 

RR (95% CI)

5

0.5

0.92 (0.20-4.23)

19

0.4

0.99 (0.38-2.56)

26

0.5

1.77 (0.84-3.69)

12

0.3

1

1

0.2

0.55 (0.07-4.37)

Total=63

 

P=0.98

Cerebral infarction death, N

Mortality per 1,000 person-years     

RR (95% CI)

15

1.5

1.09 (0.48-2.43)

60

1.2

1.11 (0.67-1.84)

40

0.8

0.86 (0.54-1.36)

43

1.1

1

7

1.6

1.00 (0.43-3.23)

Total=165

 

P=0.72

Coronary heart disease death, N

Mortality per 1,000 person-years              

RR (95% CI)

9

0.9

0.91 (0.35-2.35)

37

0.7

0.91 (0.51-1.62)

39

0.8

1.07 (0.66-1.76)

32

0.8

1

7

1.6

1.47 (0.63-3.39)

Total=142

 

P=0.54

 

 

 

Author Conclusion:

The results did not provide evidence in support of the fish hypothesis that high fish intake may be one of the factors for Japanese longevity, perhaps because the majority of the Japanese subjects in the study ate fish more than the threshold level shown to be beneficial in previous studies.

Funding Source:
Government: Ministry of Health and Welfare under the auspices of the Japanese Association for Cerebro-cardiovascular Disease Control, a research grant for CVD from the Ministry of Health, Labor and Welfare
Other: Health and Labor Sciences Research Grant
Reviewer Comments:
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? 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.) 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? 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? 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.) N/A
  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? N/A
  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? 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