Atherosclerosis 197 (2008) 290–296 Dietary intervention with oil rich fish reduces platelet-monocyte aggregation in man Jehangir N. Din a,∗ , Scott A. Harding a , Christopher J. Valerio a , Jaydeep Sarma a , Karin Lyall a , Rudolph A. Riemersma a , David E. Newby a , Andrew D. Flapan b a Centre for Cardiovascular Sciences, University of Edinburgh, Chancellor’s Building, 49 Little France Crescent, Edinburgh EH16 4SB, United Kingdom b Department of Cardiology, Royal Infirmary of Edinburgh, Edinburgh, United Kingdom Received 7 January 2007; received in revised form 25 March 2007; accepted 27 April 2007 Available online 18 June 2007 Abstract Background: Dietary intake of fish rich in omega-3 fatty acids is associated with a reduction in cardiovascular events. The mechanisms for this are uncertain and previous studies investigating effects on platelet function have produced inconsistent results. Platelet-monocyte aggregation is a sensitive marker of platelet activation and may contribute to the initiation and progression of atherothrombosis. This study assessed the effect of dietary intervention with oily fish on platelet-monocyte aggregation in healthy subjects. Methods: Fourteen subjects had their diet supplemented with 500 g of oil-rich fish per week for 4 weeks. A control group of 14 subjects received no dietary intervention over a 4-week period. Platelet-monocyte aggregates were assessed with flow cytometry. Results: Dietary intervention with fish led to an increase in omega-3 fatty acids in plasma phospholipids (14.2 ± 3.4% versus 5.8 ± 1.3%, P < 0.001). In contrast to the control group, platelet-monocyte aggregates were reduced by 35% following dietary intervention with oily fish (16.0 ± 9.0% versus 24.8 ± 10.9%, P < 0.01), and returned to basal levels 4 weeks after discontinuation of supplementation. There was an inverse correlation between platelet-monocyte aggregation and plasma omega-3 fatty acid concentrations (r = -0.421, P = 0.006). There were no changes in the plasma markers of platelet activation, soluble P-selectin or soluble CD40 ligand. Conclusions: We have demonstrated, for the first time, that dietary intervention with oil-rich fish reduces platelet-monocyte aggregation in man. Our results suggest that reduced platelet activation provides a potential mechanism through which fish oils confer their cardiovascular preventative benefits. © 2007 Published by Elsevier Ireland Ltd. Keywords: Oily fish; Omega-3 fatty acids; Platelet activation; Platelet-monocyte aggregates; Cardiovascular disease 1. Introduction Consumption of fish oil may protect against cardiovascu- lar disease [1]. Data from observational studies suggest that fish intake is inversely associated with fatal coronary heart disease [2], and randomized controlled trials of dietary fish or fish oil supplementation after myocardial infarction demon- strate a reduction in mortality [3,4]. These effects are believed ∗ Corresponding author. Tel.: +44 131 242 1850; fax: +44 131 242 6422. E-mail address: jehangirdin@hotmail.com (J.N. Din). to be due to the high amounts of omega-3 fatty acids, eicos- apentaenoic acid (EPA) and docosahexaenoic acid (DHA), present in fish oil. EPA and DHA must be obtained from dietary sources and recent guidelines from the American Heart Association recommend the consumption of oily fish at least twice weekly for individuals with and without coronary heart disease [5]. However, not all randomised controlled tri- als have shown a benefit [6], and the underlying mechanisms through which cardiac protection might be conferred remain uncertain. The effects of fish oil on platelet function and thrombosis are controversial. Although fish oils were originally thought 0021-9150/$ – see front matter © 2007 Published by Elsevier Ireland Ltd. doi:10.1016/j.atherosclerosis.2007.04.047