The effect of conjugated linoleic acid on platelet function, platelet fatty acid composition, and blood coagulation in humans.

Despite extensive research on conjugated linoleic acid (CLA) showing multiple beneficial effects in animal models, little is known about the role of dietary CLA in human health. To investigate if the beneficial effects of CLA seen in animal models are relevant to humans, we conducted a study with 17 healthy female volunteers who lived in the Metabolic Research Unit of the Western Human Nutrition Research Center for 93 d. This paper reports only the results from this study that are related to the effects of CLA supplementation on blood coagulation, platelet function, and platelet fatty acid composition. Throughout the study, the subjects were fed a low-fat diet (30 en% fat, 19 en% protein, and 51 en% carbohydrate) consisting of natural foods with the recommended dietary allowances for all known nutrients. After a 30-d stabilization period, subjects were randomly assigned to either an intervention group (n = 10) whose diet was supplemented with 3.9 g/d of CLA or a control group (n = 7) who received an equivalent amount of sunflower oil consisting of 72.6% linoleic acid with no detectable CLA. Platelet aggregation was measured in platelet-rich plasma using adenosine diphosphate, collagen, and arachidonic acid agonists. No statistical difference was detected between the amount of agonist required to produce 50% aggregation of platelet-rich plasma before and after the subjects consumed the CLA, with the exception of a decrease in response to collagen. This decrease was found in both control and intervention groups with no significant difference between the groups, suggesting that both linoleic acid (sunflower oil) and CLA might have similar effects on platelet function. The prothrombin time, activated partial thromboplastin time, and the antithrombin III levels in the subjects were determined. Again, there was no statistically significant difference in these three parameters when pre- and post-CLA consumption values were compared. The in vivo bleeding times were also unaffected by CLA supplementation (10.4 + 2.8 min pre- and 10.2 + 1.6 min postconsumption). Platelet fatty acid composition was not markedly influenced by the consumption of dietary CLA, although there was a small increase in the amount of the 9 cis,11 trans-18:2 isomer normally present in platelets after feeding CLA for 63 days. In addition, small amounts of the 8 trans,10 cis-18:2 and the 10 trans,12 cis-18:2 isomers were detected in the platelets along with traces of some of the other isomers. Thus, when compared to sunflower oil, the blood-clotting parameters and in vitro platelet aggregation showed that adding 3.9 g/d of dietary CLA to a typical Western diet for 63 d produces no observable physiological change in blood coagulation and platelet function in healthy adult females. Short-term consumption of CLA does not seem to exhibit antithrombotic properties in humans.