DLM: Omega-3 Fatty Acids (2009-2010)
Citation:
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:
To determine the role of fish and dietary n-3 fatty acid intake in the duration of the QTc interval in cardiovascular disease-free individuals from the general population.
Inclusion Criteria:
- Free-living (non-institutionalized) men and women
- At least 18 years old
- Residing in urban and rural areas of Attica near the metropolis of Athens.
Exclusion Criteria:
All individuals with any of the following were excluded from the study:
- History of cardiovascular disease
- Atherosclerotic disease
- Chronic viral infection
- Cold and flu symptoms
- Acute respiratory infection
- Dental and gout infection
- Recent surgery (previous week)
- Institutionalized.
Description of Study Protocol:
Recruitment
- 4,056 residents were recruited by random selection
- The aim was to include 78% urban and 22% rural participants
- 3,042 individuals agreed to participate
- Recruitment occured between May 2001 and December 2002.
Design
Stratified random.
Blinding Used
None.
Intervention
None.
Statistical Analysis
- Associations between categorical variables were tested using contingency tables and chi-square
- Correlations between ECG measurements and other continuous variables were evaluated using Pearson correlation coefficient for normally distributed variables
- Correlations between ECG measurements and other continuous variables were evaluated using the Spearman correlation coefficient for skewed variables
- Comparison of ECG interval variables between fish consumption were performed with ANOVA or general linear regression for fixed effects after adjusting for confounders
- Post hoc comparisons were performed using the T-test and the Z-test for continuous and binary variables, respectively.
Data Collection Summary:
Timing of Measurements
Survey and measurements were conducted once during the study period.
Dependent Variables
- QT interval: Measured and corrected using Bazetts formula
- Blood pressure: Measured three times in the right arm with subject in a sitting position
- Blood lipids (serum cholesterol, HDL, TG): Measured using chromatographic enzyme method of analysis
- LDL cholesterol: Calculated using Friedewalds formula
- Glucose analysis: Followed the World Health Organization laboratory technique.
Independent Variables
Fish consumption.
Description of Actual Data Sample:
- Initial N: 4,056 (78% urban; 22% rural participants)
- Attrition (final N): 3,042 to 1,514 men and 1,528 women (25% attrition due to participant disinterest)
- Age: 18 to 89 years old
- Ethnicity: Not specified.
Other Relevant Demographics
- Years of school
- Income
- Physical activity
- Smoking.
Anthropometrics
- Height
- Weight
- BMI.
Location
Attica area near Athens, Greece.
Summary of Results:
|
Variables |
Fish Consumption
|
Statistical Significance |
||||
|
None |
Under 150g per week |
150g to 300g per week |
Over 300g per week
|
|||
| Participants | Men N=1,514 (%) |
12
|
55
|
24
|
9
|
|
|
Women N=1,528 (%) |
9 |
58 |
25 |
8 |
|
|
| Age |
Men |
44±12 |
49±11 |
55±12 |
53±12 |
0.001 |
| Women |
44±11
|
48±12
|
53±11
|
53±14
|
||
| Education (Years) | Men |
13±4
|
12±2
|
11±4
|
10±4
|
0.001 |
|
Women |
12±4 |
11±3 |
11±3 |
9±3 |
||
| Nut Intake (Servings per Week) |
Men |
1.5±0.9 |
1.5±1.2 |
1.7±1.4 |
1.8±1.4 |
0.009 |
| Women |
1.1±0.9
|
1.4±1.2
|
1.4±1.4
|
1.7±1.2
|
||
| Current Smoker (%) | Men |
50
|
44
|
44
|
48
|
0.36
|
|
Women |
35 |
38 |
31 |
30 |
0.09 |
|
| Sedentary (%) |
Men |
60 |
62 |
53 |
52 |
0.01 |
| Women |
73
|
65
|
63
|
58
|
0.30
|
|
| Obese (%) | Men |
18
|
22
|
21
|
27
|
0.02 |
|
Women |
15 |
18 |
18 |
25 |
||
| BMI (kg/m2) |
Men |
25.9±4.6 |
26.5±4.5 |
26.4±4.9 |
27.8±5.4 |
0.01 |
| Women |
23.9±3.6
|
24.5±4.1
|
24.4±4.4
|
25.9±4.4
|
||
| Hypertension (%) | Men |
41
|
43
|
37
|
27
|
0.02
|
| Women |
45
|
32
|
28
|
21
|
||
| Blood Pressure (mmHg) | Systolic men |
135±21
|
128±22
|
125±35
|
124±25
|
0.001
|
| Systolic women |
133±20
|
125±27
|
124±25
|
121±20
|
|
|
| Diastolic men |
81±18
|
83±21
|
82±18
|
79±21
|
0.12
|
|
| Diastolic women |
79±28
|
82±22
|
84±21
|
78±22
|
0.21
|
|
| Hypercholesterolemia | Men (%) |
34
|
37
|
33
|
31
|
0.29
|
|
Women (%) |
35 |
38 |
37 |
33 |
||
| Total Cholesterol (mm per dL) |
Men |
209±41 |
197±25 |
193±32 |
189±43 |
0.31 |
| Women |
211±40
|
195+22
|
190±22
|
182+33
|
||
| HDL Cholesterol (m per dL) | Men |
44±11
|
48±15
|
49±22
|
49±13
|
0.39 |
|
Women |
53±13 |
52±11 |
51±21 |
52±16 |
||
| TG (m/dL) |
Men |
185±41 |
168±29 |
149±32 |
125±33 |
0.02 |
| Women |
188±45
|
171±32
|
145±33
|
131±32
|
||
| Diabetes Mellitus (%) | Men |
6
|
10
|
10
|
9
|
0.19 |
|
Women |
6 |
7 |
7 |
10 |
||
| RR Interval |
Men |
0.83±0.01 |
0.87±0.01 |
0.88±0.01 |
0.89±0.01 |
0.13 |
| Women |
0.81±0.01
|
0.82±0.01
|
0.83±0.01
|
0.85±0.01
|
0.55
|
|
| QT Interval | Men |
0.39±0.01
|
0.37±0.02
|
0.36±0.03
|
0.35±0.02
|
0.001
|
|
Women |
0.38±0.01 |
0.37±0.02 |
0.37±0.02 |
0.36±0.02 |
0.06 |
|
| QT Interval (Corrected) | Men |
0.44±0.01
|
0.42±0.01
|
0.40±0.01
|
0.38±0.02
|
0.02
|
|
Women |
0.45±0.01 |
0.43±0.01 |
0.42±0.01 |
0.39±0.02 |
0.03 |
|
Other Findings
- A positive association was found between the amount of fish consumed and age
- There was an inverse relationship between fish intake and years of school, triacylglycerols and systolic blood pressure in men
- Women consuming fish more than once per week were older, less educated, more likely to be obese and less likely to have hypertension and lower tTG concentration
- A significant decrease based on the amount of fish consumed was observed in the QT interval of both men and women
- The QT interval was inversely associated with fish intake in men and less significant in women
- The QT interval was significant even after adjustments were made for physical activity status, BMI, smoking habits, annual income, years of school, intake of nuts and the presence of hypertension, diabetes and hypercholesterolemia
- Cut off analysis showed that a fish intake of 300g per week was optimal for maximizing the likelihood of a QTc interval below 0.45 seconds.
Author Conclusion:
Long-term fish consumption resulted in protective effects against cardiac arrhythmia in non-institutionalized Mediteranean population with no prior evidence of cardiovascular disease.
Funding Source:
| Not-for-profit |
|
Reviewer Comments:
- Only a small number of participants consumed the maximum amout of fish per week
- Consumption was self-reported and was collected only once using a food frequency questionnaire. There was no measure in place to help verify the information collected.
- The types of fish eaten were not specified. The amount of fat and fatty acid in fish vary based on the type of fish eaten. For example, white as opposed to oily fish. This detail would have been good to know.
- Biochemical measures were conducted and recorded only once. Repeated measures could have been taken, especially since the project lasted more that 12 months.
- Overall a relatively good study.
|
Quality Criteria Checklist: Primary Research
|
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| 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) | 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.) | 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")? | Yes | |
| 4. | Was method of handling withdrawals described? | ??? | |
| 4.1. | Were follow-up methods described and the same for all groups? | N/A | |
| 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%.) | ??? | |
| 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? | Yes | |
| 5. | Was blinding used to prevent introduction of bias? | No | |
| 5.1. | In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? | No | |
| 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? | 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? | N/A | |
| 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? | N/A | |
| 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? | N/A | |
| 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? | Yes | |
| 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 | |