Alpha tocopherol is a type of vitamin E that exists naturally as d-alpha tocopherol, but supplement manufacturers also market synthetic "mirror image" l-alpha tocopherol as well as a mixture of d- and l-alpha tocopherol.
The synthetic kind and the mix are cheaper, but l-alpha tocopherol has little or no actual vitamin E activity in the body. It may interfere with d-alpha tocopherol activity and there's no long-term safety data.
When buying vitamin E supplements, be sure to choose d-alpha tocopherol along with other natural tocopherols such as beta-, gamma- and delta-.
1. Gaby, A. Does high-dose vitamin E kill people? Townsend Letter for Doctors and Patients. Available at: http://findarticles.com/p/articles/mi_m0ISW/is_259-260/ai_n10299312/pg_2. Accessed on Oct. 25, 2008.