The source of the vitamin E used for supplementation is also very important. There are many forms of vitamin E. the preferred type (most biologically active form) is know as alpha-tocopherol. It is recommended that alpha-tocopherol, alpha-tocopherol acetate, or alpha-tocopherol succinate be used. Other forms of vitamin E (gamma-tocopherol, beta-tocopherol) do not provide the same level of protection within the body that alpha-tocopherol does. Avoid cheap vitamin E supplements that contain high levels of vitamin A. Providing this type of vitamin supplement to dogs on a long term basis could lead to an overdose of vitamin A and possibly lead to vitamin A toxicity.