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Twenty healthy, non-smoking subjects were enrolled into a study to investigate the effects of dietary supplementation with essential fatty acid (EFAs) on red blood cell rheology. Ten subjects were given 3 months dietary supplementation with long chain polyunsaturated EFAs containing omega–3 and omega–6 EFAs while 10 others were given placebo (sunflower oil). Venous sampling was performed at 0 and 12 weeks and red blood cell (RBC) aggregation and deformability measured by a filtration system. The results showed a reduction in RBC aggregation in the group given omega-3 and omega-6 EFAs but not in the placebo group. This may be related to changes in the RBC membrane and surface receptor characteristics. Such EFAs may be useful in Raynaud's phenomenon. Copyright 1999 Harcourt Publishers Ltd

1. We have previously shown a circadian variation in leucocyte activation and endothelial function which may explain why some inflammatory and vascular diseases show a circadian variation in disease activity/occurrence. 2. We have investigated the circadian variation of two soluble cell adhesion molecules, intercellular adhesion molecule-1 and E-selectin, in 10 healthy volunteers. Soluble intercellular adhesion molecule-1 is released from both activated leucocytes and endothelial cells while soluble E-selectin is released only from activated endothelium. 3. Results show a circadian variation exists for both soluble intercellular adhesion molecule-1 and E-selectin (both P < 0.0001, analysis of variance) with a peak activity at 12:00 h for both measures and a minimum activity at 04:00 h for intercellular adhesion molecule-1 and 00:00 h for E-selectin. 4. These results demonstrate the existence of a diurnal variation in cell adhesion molecules, providing evidence in support of a diurnal pattern in endothelial and leucocyte activation. An alteration in this biological rhythm may help to explain the diurnal variation in disease activity in certain inflammatory and vascular disease states. Furthermore, it stresses the importance of sample time point standardization in clinical studies.