Polyunsaturated Fats and Risk of Primary Cardiac Arrest

BACKGROUND: The potential role of omega-3 PUFA intake in the prevention of coronary heart disease is supported by studies among Greenland Eskimos, the Japanese, the Dutch, and data from the Western Electric Study. The low incidence of coronary heart disease among Eskimos and Japanese populations has been attributed to high dietary intake of fish oils. In addition, a large cohort study from the Netherlands found an inverse relationship between regular fish consumption and coronary heart disease mortality. Mortality from coronary heart disease was increased 2.5 fold among persons who did not consume fish compared to those who consumed at least 30 grams/day or the equivalent of 1-2 fish meals per week. There was no evidence that increasing fish intake above 30 grams per day provided additional benefit; moderate intake had the greatest effect on coronary heart disease mortality. Dietary omega-3 PUFA intake, though modest, was also inversely related to coronary heart disease mortality. Analysis of dietary data from the Western Electric Study cohort also suggested an inverse relation between fish consumption and coronary heart disease mortality. In contrast, cohort studies from Hawaii and Norway observed no relation between fish consumption and coronary heart disease. However, fish consumption was higher in these populations and there were few individuals who did not consume fish. Prior to the present study, there had been no studies of the relation between dietary fish intake and the risk of primary cardiac arrest. DESIGN NARRATIVE: The study has a case-control design. Beginning in July 1990, through Emergency Medical Service incident reports, all cases of primary cardiac arrest, ages 25-74, without prior clinical heart diseases, were identified in Seattle and suburban King County, Washington during the period April 1990 to March 1994. Controls were identified from the same community using random digit dialing. Blood specimens from cases and controls were analyzed to determine red-cell membrane fatty acid composition. Spouses of cases and controls were interviewed to assess dietary intake of long-chain omega-3 PUFAs (a function of the amount of seafood consumed), usual fat consumption, changes in dietary intake, and presence or absence of other risk factors for primary cardiac arrest. Analyses were conducted to assess the relation between dietary intake and red-cell membrane omega-3-fatty acid levels and to assess whether there was a threshold or dose response effect for each fatty acid. The study was renewed in 1996 through June, 2000. During the initial funding period studies were conducted on the relationship to primary cardiac arrest of dietary intake of long chain n-3 polyunsaturated fatty acids from seafood. The investigators are now extending the population-based, case-control study to determine whether the dietary intake of trans-fatty acids derived from partially hydrogenated unsaturated fatty acids measured through a biomarker are directly associated with the risk of primary cardiac arrest. Cases of PCA who were attended by paramedics in King County, Washington are identified. Demographically similar controls are identified from the same community using random digit dialing. Blood specimens from both previously identified and newly identified cases (collected by paramedics in the field) and controls are analyzed for red cell membrane total trans-fatty acid levels. This serves as a biomarker of dietary trans-fatty acid intake. Spouses of subjects are interviewed to obtain information on usual saturated fat intake, recent changes in diet and other risk factors. Additionally, among spouses of newly identified subjects, the types of fat used in cooking and as spreads are assessed. Analyses focus on the relationship between red cell membrane total trans-fatty acid levels and the risk of PCA after adjusting for saturated fat intake and other risk factors. The investigators also plan to extend a detailed diet substudy in a subset of control subjects to confirm the relationship between the dietary intake of trans-fatty acids and red cell membrane levels and evaluate whether the relationship is independent of other nutrients. The study has been renewed through March 2006.