[Dietary intake of n-3 fatty acids and the risk of acute myocardial infarction: a case-control study]

The SUN cohort study (Seguimiento University of Navarra)

OBJECTIVE

Cohort study (the SUN project) to identify dietary determinants of hypertension, diabetes, obesity and coronary heart disease (CHD), among other conditions.

DESIGN

The SUN project is a Mediterranean dynamic prospective follow-up (cohort) study assessing participants every 2 years. The recruitment started in 2000 and it is permanently open (this is a dynamic cohort). A preliminary case-control study of myocardial infarction was also conducted, selecting incident cases of myocardial infarction and matched hospital controls.

SETTING

The SUN study is conducted in Spain with university graduates, most of them being former students of the University of Navarra. The case-control study was conducted in three tertiary hospitals in the city of Pamplona (Spain).

SUBJECTS

The case-control study included 171 cases and 171 controls. We have currently enrolled more than 17,500 participants in the SUN cohort. Approximately 7500 of them were enrolled less than 2 years ago, and have not received yet the invitation to complete the 2-year follow-up assessment. The follow-up rate for the first 10,000 participants approaches 90%.

RESULTS

The case-control study found inverse associations between olive oil (or adherence to a Mediterranean food pattern) and myocardial infarction. In the SUN cohort, after 28.5 months of follow-up a higher adherence to a Mediterranean food pattern rich in olive oil was associated with a reduced risk of hypertension, though the results were statistically significant only among men.

CONCLUSIONS

The SUN study and the accompanying case-control study support the benefits of a Mediterranean diet and olive oil against CHD and hypertension.

Development of a short dietary intake questionnaire for the quantitative estimation of adherence to a cardioprotective Mediterranean diet

Our objective was to develop a short questionnaire that can be easily used to estimate quantitatively the level of adherence to cardioprotective Mediterranean diets. The short questionnaire assessed the consumption of cardioprotective elements included in the Mediterranean diet (olive oil, wine, fruits, vegetables, fish, legumes and whole-grain intake). A low consumption of meat or meat-products was also included in the composite score. The relative risk of myocardial infarction for each category of the composite score obtained (range 0-9) was computed using data from a case-control study that included 171 cases of first myocardial infarction and 171 matched controls. We found an adjusted odds ratio=0.18 (95% confidence interval (CI): 0.03-0.97; P=0.04) for those scoring 7-9 points when comparing them with those scoring 1-2 points. An increment of one point in the score was associated with an 18% reduction in the relative risk of myocardial infarction (P=0.05).

[Fish omega-3 fatty acids and risk of coronary heart disease]

A great amount of evidence from epidemiological studies and clinical trials supports a protective effect against coronary heart disease for fish consumption and intake of marine omega-3 fatty acids. Biological pathways for this risk reduction include membrane stabilization in the cardiac myocite, inhibition of platelet aggregation, favourable modifications of the lipid profile, decrease in blood pressure and reduction of the inflammatory response of the endothelium. Results from epidemiological studies suggest a threshold effect for the consumption of fish and omega-3 fatty acids. Risk reduction is especially important for cardiac sudden death. Nevertheless, protection against non-fatal coronary heart disease has also been observed. Recently published studies have shown that mercury intake, present in high concentrations in fish, could counteract the beneficial effect from fish consumption.

Dietary folate and the risk of nonfatal myocardial infarction

BACKGROUND

Elevated homocysteine levels have been associated with a higher risk of cardiovascular disease. Because folate intake can reduce homocysteine levels, we investigated the association between dietary folate intake and nonfatal myocardial infarction.

METHODS

We conducted a case-control study in three tertiary hospitals of Pamplona, Spain, between 1999 and 2001. Study physicians enrolled 171 patients less than 80 years of age with a first nonfatal myocardial infarction and 171 control patients matched by age, sex, hospital and calendar month. We excluded patients with any prior major cardiovascular disease. Participants were interviewed about medical factors and life-style and completed a food frequency questionnaire previously validated in Spain. We calculated energy-adjusted intakes of folate and estimated relative risks (RRs) of myocardial infarction and 95% confidence intervals (CIs) using conditional logistic regression. Relative risks were adjusted for conventional risk factors.

RESULTS

Only 6% of participants were taking vitamin supplements. The main sources of folate were green leafy vegetables, green beans, oranges, peppers and lettuces. The estimated matched RR of myocardial infarction for the top three quartiles of folate intake (, above 340 microg/day) was 0.57 (CI = 0.35-0.94), compared with the lowest quartile of intake. The multivariate adjusted RR was 0.51 (CI = 0.24-1.06). There was no apparent dose effect above this threshold.

CONCLUSIONS

Our results in a Mediterranean population with natural plant foods as the main source of folate provide further evidence to support the hypothesis that dietary folate intake may be an independent protective factor for myocardial infarction. The magnitude of the effect, its biological plausibility, and the consistency across studies offer support for a causal association.