Submitted to: Journal of Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/17/1995
Publication Date: N/A
Interpretive Summary: A substance called gamma-tocotrienol has been shown to lower cholesterol levels in humans and experimental animals when added to the diet in small quantities. It is difficult to obtain enough pure gamma-tocotrienol for nutritional studies, so many investigators use Palmvitee, a mixture of alpha-tocopherol and alpha-, gamma-, and delta-tocotrienol obtained from palm oil. Results with Palmvitee have been inconsistent. We fed chickens diets that were supplemented with only gamma-tocotrienol or with mixtures of gamma-tocotrienol and alpha-tocopherol, and then we measured the levels of cholesterol in the blood. The results showed that the addition of alpha-tocopherol reduced or eliminated the cholesterol-lowering effect of the gamma-tocotrienol. We then compared literature reports where Palmvitee was used. In those studies where cholesterol was lowered, the proportion of gamma-tocotrienol in the Palmvitee was high, whereas in the studies where Palmvitee had little or no effect, its proportion of gamma-tocotrienol was low and alpha-tocopherol was high. This finding explains the inconsistent results with Palmvitee, and shows that investigators using Palmvitee need to ensure that batches with a high ratio of gamma-tocotrienol:alpha-tocopherol are used.
Technical Abstract: The concentration-dependent impact of gamma-tocotrienol on serum cholesterol can be traced to the posttranscriptional down-regulation of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase activity. In dietary studies this effect is near maximally realized with 0.07 nmol gamma-tocotrienol/g diet. Numerous studies with young chickens also show the tumor-suppressive efficacy of gamma-tocotrienol. Palmvitee, the tocotrienol-rich fraction of palm oil, is currently the sole commercial source of gamma-tocotrienol. Contrary to the universal findings of the efficacy of gamma-tocotrienol there are conflicting reports of the impact of Palmvitee, which also contains alpha-tocopherol on the cholesterol-suppressive action of gamma-tocotrienol. We now report that increasing the proportion of alpha-tocopherol in tocol blends containing adequate gamma-tocotrienol to suppress HMG-CoA reductase activity results in an attenuation of the tocotrienol action. A summary of Palmvitee preparations shows that effective preparations consist of 15-20% alpha-tocopherol and approximately 60 percent gamma- and delta-tocotrienol whereas ineffective preparations consist of equal or greater than 30 percent alpha-tocopherol and 45 percent gamma and delta-tocotrienol.