Higher levels of omega-6 fatty acid in the blood were associated with a lower risk of coronary heart disease (CHD), results of a nested case-control study found.
Patients with the highest plasma concentration of omega-6 polyunsaturated fatty acids had a significantly lower risk of CHD compared with those who had the lowest concentrations (adjusted OR 0.84 95% CI 0.76 to 0.92, P<0.0001), according to Kay-Tee Khaw, MA, MSc, FRCP, of the University of Cambridge in the U.K., and colleagues.
They also saw a weak but significant relationship between higher blood levels of saturated fatty acids and greater risk of CHD, Khaw and co-authors wrote in the July issue of PLoS Medicine.
The study assessed the relationship between plasma concentrations of various saturated and polyunsaturated fatty acids and incident CHD in 2,424 patients -- including 633 fatal incidents -- versus 4,930 patients who were alive and had no cardiovascular disease.
Participants were gathered through the European Prospective Investigation into Cancer (EPIC)-Norfolk, and included patients, ages 40 to 79 at baseline, from 1993 to 1997 who were followed until 2009.
They completed a questionnaire on medical history, smoking, alcohol intake, physical activity, social class, and education. Blood samples were taken at baseline and were evaluated for concentrations of 22 different phospholipid fatty acids.
The types of fatty acids were grouped into six "families:"
- Even chain saturated
- Odd chain saturated
- Omega-6 polyunsaturated
- Omega-3 polyunsaturated
- Trans-fatty acids
At follow-up, concentrations of these families of fatty acids were compared against the development of CHD, with adjustments for age, sex, body mass index, and other factors recorded in the questionnaire.
Omega-6 polyunsaturated fatty acid concentration had a significant inverse association with risk of developing CHD, as did odd chain saturated fatty acids (RR 0.67, 95% CI 0.54 to 0.80) when comparing those with highest versus lowest concentrations of plasma fatty acid.
There was "no overall significant relationship between total plasma phospholipid fatty acid concentration and CHD," the researchers wrote. However, there was an increased strength and significance of the association between CHD and saturated fatty acids with adjustment for other fatty acid concentrations (OR 1.83, 95% CI 1.37 to 2.46, P<0.0001) for those with the lowest versus highest concentrations of saturated fatty acids.
The risk was "attenuated after adjusting for cholesterol levels, indicating that much of the association between saturated fatty acid and CHD is likely to be mediated through blood cholesterol levels," Martijn Katan, PhD, of the Vrije Universiteit in Amsterdam, wrote in an editor's summary.
Khaw and colleagues also noted that the lack of association with saturated fat intake and CHD was "unsurprising given the large measurement errors in dietary assessment of fat intake through recall errors, ubiquity of fats leading to quantification difficulties, and, critically, huge variability in fatty acid composition of foods such that discrimination between different fats is problematic."
The authors noted several limitations with the study, including a priori hypotheses for main fatty acid family analyses, only measuring the two most common trans-fatty acids, and use of plasma fatty acid measures from one point in time. Katan added that the study was limited by the exclusion of nondiet factors' contributions to changes in plasma fatty acid levels.
Both Katan and the researchers said future research could include an evaluation of biological and health effects on individual fatty acids. The authors also said that future research should include overall fatty acid profiles and balances between fatty acids.
The team concluded that dietary recommendations should evolve to discriminate between individual fatty acids and their interactions with each other and a patient's metabolism.
From the American Heart Association:
The study was supported by the Medical Research Council U.K. and Cancer Research U.K.
The authors declared no conflicts of interest.