Risk of first non-fatal myocardial infarction negatively associated with olive oil consumption: a case-control study in Spain

474_N01-268 8/4/2002 4:07 pm Page 474 (Black plate) © International Epidemiological Association 2002 Printed in Great Britain International Journal of Epidemiology 2002;31:474–480 CARDIOVASCULAR DISEASE Risk of first non-fatal myocardial infarction negatively associated with olive oil consumption: a case-control study in Spain E Fernández-Jarne,a,b E Martínez-Losa,a,c M Prado-Santamaría,a,c C Brugarolas-Brufau,a,c M Serrano-Martíneza,c and MA Martínez-Gonzáleza Background Olive oil is the main source of dietary lipids in most Mediterranean countries where mortality and incidence rates for coronary heart disease (CHD) are the lowest in Europe. Although international comparisons and mechanistic reasons support the hypothesis that a high olive oil intake may prevent CHD, limited data from studies of individuals are available. Methods A hospital-based case-control study was conducted in Pamplona (Spain) recruiting 171 patients (81% males, age ,80 years) who suffered their first acute myocardial infarction and 171 age-, gender- and hospital-matched controls (admitted to minor surgery, trauma or urology wards). A validated semi-quantitative food frequency questionnaire (136 items) was used to appraise previous long-term dietary exposures. The same physician conducted the face-to-face interview for each case patient and his/her matched control. Conditional logistic regression modelling was used to take into account potential dietary and non-dietary confounders. Results The exposure to the upper quintile of energy-adjusted olive oil (median intake: 54 g/day) was associated with a statistically significant 82% relative reduction in the risk of a first myocardial infarction (OR = 0.18; 95% CI : 0.06–0.63) after adjustment for dietary and non-dietary confounders. Conclusions Our data suggest that olive oil may reduce the risk of coronary disease. These findings require confirmation in further observational studies and trials. Keywords Diet, epidemiology, coronary disease, fatty acids Accepted 10 October 2001 Dietary patterns found in olive-growing areas of the Mediterranean region have been postulated as protective against coronary heart disease (CHD).1 Olive oil, rich in monounsaturated fatty acids (MUFA), is the main source of dietary lipids in most Mediterranean countries. The very low CHD mortality rates found in Mediterranean countries, together with a wide array of mechanistic reasons, have led to the idea that instead of recommending a low-fat diet to prevent CHD, it would be worthwhile to give the population a Department of Epidemiology and Public Health, University of Navarre, Pamplona, Spain. b Department of Cardiology. University Clinic of Navarre, Spain. c Navarre Primary Care Health Services, Spain. Correspondence: Prof. Miguel Ángel Martínez-González, Epidemiología y Salud Pública, Facultad de Medicina, Universidad de Navarra, Irunlarrea 1, E-31080 Pamplona, Spain. E-mail: the message of augmenting the intake of olive oil, while avoiding animal and trans-fats.2,3 A widespread recommendation promoting olive oil consumption to replace saturated and transunsaturated fat needs to be solidly based on epidemiological findings conducted in populations where consumption levels are high and heterogeneous. Apart from international comparisons and ecological correlations, and the outstanding findings of the Seven Countries Study,4 there is little direct evidence from analytical epidemiological studies relating diet to CHD in Mediterranean countries. A small randomized trial of corn oil and olive oil carried out almost 40 years ago by GA Rose found no benefit for olive oil and even an adverse significant effect for corn oil in 80 coronary patients after 2 years of follow-up.5 A case-control study in Italian women (287 cases/649 controls) reported no significant benefit for oil consumption (odds ratio [OR] = 0.7 for the second tertile and 1.1 for the third).6 A case-control study in Greece did not find any significant protection from MUFA intake.7 474 474_N01-268 8/4/2002 4:07 pm Page 475 (Black plate) OLIVE OIL CONSUMPTION AND MYOCARDIAL INFARCTION The same group8 found that an a priori defined Mediterranean dietary pattern was associated with advantageous survival in a cohort of elderly people. Three other small studies have consistently reported similar results in Australia,9 Spain10 and Italy11 using analogous methodologies. However, the outcome in all of these four studies included every cause of death and no information about the specific role of olive oil on CHD risk was reported. A randomized secondary prevention trial conducted in France12 showed an impressive protection provided by an experimental Mediterranean diet on the risk of death and reinfarction among survivors of a first acute myocardial infarction (AMI). Nevertheless, as the major element of the assigned diet was an experimental canola-oil based margarine and the diet simultaneously included a high intake of alpha-linolenic acid, fruit and vegetables, it was not possible to attribute its benefit to a single factor. In addition, the nutritional factors associated with primary and secondary prevention of CHD need not to be the same. The aim of our study was to assess the potential role of olive oil for the primary prevention of CHD and to quantify the reduction in the risk of a first AMI that can be provided by a high dietary olive oil intake. Methods Cases were defined as male or female subjects, aged under 80, survivors of a first AMI (ICD code 410) admitted to one of the three tertiary hospitals of Pamplona (Spain) within the periods October 1999–June 2000 or October 2000–February 2001. They had to fulfil the criteria13 for definite AMI of the MONICA project (two or more ECG showing specific changes; ECG showing probable changes plus abnormal cardiac enzymes; or typical symptoms plus abnormal enzymes). A previous history of angina pectoris, a previous diagnosis of CHD or other prior diagnosis of major cardiovascular disease were exclusion criteria. Informed consent was obtained from the patients and the project was approved by the Institutional Review Board of the Medical School. We identified 180 eligible cases. Nine of them refused to participate (participation = 95%). A control subject of the same age (5-year bands), gender and hospital was matched to each case. Eligible controls were patients admitted to the surgical, trauma or urology wards of the same hospital during the same month that matched cases for diseases believed to be unrelated to diet. Eight eligible controls refused to participate (participation: 96%) and each of them was replaced by other patients of similar characteristics for matching variables. Cases and controls were interviewed in a standard way with the same questionnaire. All interviews were conducted by four physicians belonging to the research team (EFJ, EML, MP, CB). The same physician who interviewed a case patient also interviewed the respective matc (...truncated)