OBJECTIVE: To investigate whether fish oil affects cardiovascular risk factors during the adolescent growth spurt. STUDY DESIGN: A total of 78 boys age 13-15 years with a mean body fat percentage of 30% +/- 9% were randomly assigned to consume fish oil (providing 1.5 g of n-3 long-chain polyunsaturated fatty acid/day) or vegetable oil (control) for 16 weeks. The oils were included in bread. RESULTS: After the intervention, the red blood cell (RBC) content of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) were 1.2% +/- 0.5% and 6.7% +/- 1.6%, respectively, in the those receiving fish oil (FO group), compared with 0.6% +/- 0.3% and 4.1% +/- 0.9% in the control group. Systolic blood pressure (SBP) was 3.8 +/- 1.4 mm Hg lower (P <.006) and diastolic blood pressure (DBP) was 2.6 +/- 1.1 mm Hg lower (P <.01) in the FO group compared with the control group. Plasma triacylglycerol (TAG) concentration and insulin sensitivity were unaffected by either of the treatments. Plasma high-density lipoprotein (HDL) and non-HDL cholesterol were increased by 5% and 7%, respectively, in the FO group, and by 2% and 0% in the control group (P <.01-.02). The changes in RBC EPA content were inversely correlated with the changes in SBP and DBP and directly correlated with the increases in HDL cholesterol and non-HDL cholesterol concentrations. No association was seen between RBC EPA and plasma TAG concentration or insulin sensitivity. CONCLUSION: Fish oil improves BP in normotensive and normolipidemic slightly overweight adolescent boys. Copyright © 2010 Mosby, Inc. All rights reserved.