EAL

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

Citation:

Study Design:

Class:

- Click here for explanation of classification scheme.

Quality Rating:

Research Purpose:

The relationships between the consumption of fish and fish-specific fatty acids and the risk of coronary heart disease were investigated among men and women drawn from a population-based cohort in Finland.

Inclusion Criteria:

30 to 79 years or older
No previous diagnosis of heart disease
Participated in a health examination survey from 1967 to 1972.

Exclusion Criteria:

Less than 30 or greater than 79 years of age
History of heart disease at baseline.

Description of Study Protocol:

Recruitment

Subjects recruited out of the Finish Mobile Clinic from 1966 to 1972.

Design

Subjects were randomly selected for an interview on their dietary habits. At baseline, data on total habitual food consumption during the preceding year were collected using a dietary history interview method. A pre-formed questionnaire listing more than 100 different foods and food groups was used to guide structured interviews. The type of fish and method of preparation was specified during the interview. A total of 26 different fish items were recorded in the interviews. Data on demographic characteristics, smoking, diseases and medicines were provided by a self-administered questionnaire. Blood samples were collected and total cholesterol concentration in serum samples was determined by an autoanalyser modification of the Liebermann-Burchard reaction.

Statistical Analysis

The relative risks of mortality in the quintiles of fish and other dietary components, using the lowest quintiles as the referent category were computed based on Cox's model. For these analyses, the intakes of fatty acids were first adjusted by the residual method. Age and energy intake were included in the model as continous variables. In further analysis, potential non-dietary confounders were added to the model: BMI and serum cholesterol were included as continous variables and geographical area, smoking, hypertension, occupation and diabetes were added as categorical variables. In additional analyses, several dietary factors were also taken into account by adding them as continuous variables in the model.

Data Collection Summary:

Timing of measurements: Initial interview then follow-ups occurring until 1992
Dependent variables: Risk of coronary heart disease
Independent variables: Intake of fish and long-chain omega-3 fatty acids.

Description of Actual Data Sample:

Initial N: 2,775 men and 2,445 women
Age: 30 to 79 years of age
Ethnicity: Finnish
Location: Finland.

Summary of Results:

The intake of fish-specific N-3 fatty acids was not significantly associated with the risk of CHD in either men or women
Fish intake was closely associated with the intake of the fish-specific fatty acids, EPA and DHA. However, several general risk factors of coronary heart disease, e.g., smoking, serum cholesterol and BMI, tended to be higher at higher levels of fish consumption and more so in men
Total fish consumption was not significantly associated with coronary heart disease in men. Freshwater fish consumption, but not seawater fish, tended to be associated with a higher risk of coronary heart disease.
Men with high levels of fish consumption also had an overall higher level of general coronary heart disease risk factors than women.

Adjusted Relative Risks of Coronary Heart Disease in Quintiles of Fish Consumption and Intakes of Long-Chain Omega-3 Fatty Acids in Women

	Quintile of Dietary Variable One	Quintile of Dietary Variable Two	Quintile of Dietary Variable Three	Quintile of Dietary Variable Four	Quintile of Dietary Variable Five	P for Trend
Total Fish Range in Quintile (grams/day)	<8	9-15	16-24	25-40	>41
Age and Energy-Adjusted Relative Risk (95% confidence interval)	1	0.86 (0.54, 1.35)	0.79 (0.50, 1.25)	0.70 (0.44, 1.13)	0.63 (0.39, 1.02)	0.04
Multivariate Adjusted Relative Risk (95% confidence interval)	1	0.91 (0.57, 1.47)	0.77 (0.48, 1.23)	0.68 (0.42, 1.12)	0.59 (0.36, 0.99)	0.02
Long-Chain N-3 Fatty Acids Multivariate Adjusted Relative Risk (95% confidence interval)	1	0.67 (0.40, 1.13)	1.14 (0.72, 1.79)	0.75 (0.46, 1.23)	0.73 (0.44, 1.19)	0.31

Other Findings

In the present study, higher fish consumption was associated with a lower risk of coronary heart disease in analysis, including energy intake and non-dietary confounders, but after further adjustment for several potential dietary confounders, the association was less significant.

The present findings may indicate that the suggested beneficial association of fish consumption is due to other dietary factors shown to be associated with fish consumption. The fact that the intake of fish-specific fatty acids was not found to be associated with the disease risk, gives further support for this notion.

Author Conclusion:

Our present study results support the suggested beneficial effect of fish consumption against coronary heart disease in women. However, potential confounding due to better dietary habits associated with fish consumption cannot be excluded.
Fish consumption was not found to offer protection against the development of coronary heart disease in men, who were characterized by a high level of general coronary heart disese risk factors.

Funding Source:

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)	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?		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%.)	No
	4.3.	Were all enrolled subjects/patients (in the original sample) accounted for?	Yes
	4.4.	Were reasons for withdrawals similar across groups?	No
	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.)	N/A
	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?	N/A
	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)?	Yes
	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?	No
	10.2.	Was the study free from apparent conflict of interest?	Yes