EAL

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

Citation:

Study Design:

Class:

- Click here for explanation of classification scheme.

Quality Rating:

Research Purpose:

Prospective examination of the the association between fish consumption and sudden cardiac death among male physicians enrolled in the Physician's Health Study.

Inclusion Criteria:

This study uses the same inclusion criteria for the Physician's Health Study, including US male physicians who were 40 to 84 years old in 1982 and had no history of myocardial infarction, stroke, transient ischemic attack or cancer (except nonmelanoma skin cancer). At baseline, the physicians completed questions on health status and risk factors for cardiovascular disease, including alcohol and vitamin use, dietary intake of selected foods and exercise.

Additionally, the physicians who were included in this study were required to return the 12-month questionnaire, answer two questions regarding fish consumption and were not taking fish oil supplements.

Exclusion Criteria:

Excluded for this study were physicians who:

Had a history of myocardial infarction, cerebrovascular disease or cancer
Died prior to returning
Failed to return the 12-month questionnaire
Didn't answer fish questions on survey
Were taking fish oil supplements.

Description of Study Protocol:

22,071 US male physicians aged 40 to 84 years were followed for 11 years as part of a randomized trial of aspirin and beta-carotene.

Data Collection Summary:

Baseline data: Questionnaires to evaluate health status, risk factors for CVD (alcohol and vitamin use, exercise, dietary intake using semiquantitiative FFQ at 12 and 18 months). At 12 months, FFQ included frequency and amounts of intake of four kinds of fish and shellfish. The use of fish oil tablets was reported at five years. Initially at six months and then at one year, follow-ups, health status and CVD disease was monitored with repeat questionnaires.
Outcome measures: Sudden cardiac death.

Description of Actual Data Sample:

20,551 male physicians were included in the analysis:

3.1% (637) reported rarely or never consuming fish
10.8% reported eating fish more than five times a week
80% consumed fish between one and four times a week
Mean level of consumption was 2.5 meals per week.

Summary of Results:

133 sudden deaths (0.6%) occurred over the 11 years of the study. After controlling for age, randomization to aspirin and beta-carotene, and coronary risk factors, dietary fish intake was associated with a decreased risk of sudden death, with an apparent threshold effect at a consumption level of one fish meal per week (P=0.03). For men who consumed fish at least one time a week, the RR of sudden death was 0.48 (95% CI, 0.24 to 0.96; P<0.04), compared to men who consumed fish less than once a month. The consumption of fish at least once a week may decrease the risk of sudden cardiac death in men.

Author Conclusion:

The method for evaluating fish intake (amounts) and the kind and amounts of fish oil appeared to be qualitative rather than quantitative
All levels of fish consumption were associated with a decreased risk of sudden death, but the size of the reduction did not appear to differ substantially at levels of consumption greater than one fish serving per week, suggesting a threshold effect. This small amount of fish may be sufficient to provide an essential amount of long-chain n-3 polyunsaturated fatty acid or some unidentified nutrient or both that decrease sudden cardiac death.

Funding Source:

Government:

NHLBI, National Cancer Institute

Reviewer Comments:

Recommending fish consumption at least one time per week could help patients lower their risk for sudden death. More studies are need to determine the actual mechanisms or nutrients which are responsible for the positive effects of n-3 fatty acids from fish.

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?	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?	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?	Yes
	6.5.	Were co-interventions (e.g., ancillary treatments, other therapies) described?	Yes
	6.6.	Were extra or unplanned treatments described?	No
	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