Vitamin E consists of eight isomers (four tocopherol isomers and four tocotrienol isomers). α-Tocopherol was the first form of vitamin E discovered back in the 1920s and is the most abundant form found in the body’s tissues. Since that time α-tocopherol had been considered the main form of vitamin E.
According to a new review just published two weeks ago in Molecular Carcinogenesis, researchers investigated the studies on vitamin E and cancer prevention, specifically discussing the different isomers and their effects.
Over the past several decades there had been a significant amount of α-tocopherol research demonstrating it mainly as an antioxidant, while the mid-1970s saw the emergence of tocotrienol research. This research not only demonstrated tocotrienols’ beneficial effects as an antioxidant but also showed significant positive clinical outcomes in cardiovascular disease, osteoporosis, metabolic syndrome, non-alcoholic fatty liver disease (NAFLD), and cancer. As α-tocopherol research continued, large studies did not show a cancer-protective effect. On the other hand, recent studies have investigated the effects of other tocopherol isomers as well as tocotrienols, demonstrating stronger cancer-protective effects.
Due to these negative studies of α-tocopherol in cancer, there are no cancer-protective properties seen in individuals with sufficient vitamin E status. Vitamin E as α-tocopherol is easily obtained in the diet from food such as nuts, seeds, spinach, avocado, olive oil, and broccoli. The issue with α-tocopherol comes from additional supplementation on top of dietary sources. α-Tocopherol is stored in the tissue and not metabolized in the same way as other vitamin E isomers; therefore, supraphysiological doses of α-tocopherol interfere with the actions of these other isomers. For example, high doses of α-tocopherol decrease blood and tissue levels of gamma-tocopherol, which may have strong anti-inflammatory and cancer-protective effects. In addition, other studies have demonstrated α-tocopherol interfering with the clinical benefits and absorption of tocotrienols.
Previous research providing α-tocopherol at daily doses between 200 - 400 mg did not have an effect on colon, lung, prostate, or other cancers, and in follow up studies actually demonstrated an increased risk in some cancers. Safety studies have shown no negative effect of tocotrienol supplementation, with doses being given up to 3200 mg per day. Clinical studies in cancer have used doses of delta and gamma tocotrienols at 300 mg two to three times per day.
One recent phase II trial in Denmark that included 23 patients with recurrent ovarian cancer was published last year in Pharmaological Research. These patients were given 300 mg of delta and gamma tocotrienols three times a day as an adjunctive treatment with chemotherapy. The survival rate was extended to 10.9 months from 5 to 7 months, which may be related to the addition of tocotrienols.
Based on the entire body of research on different vitamin E isomers, α-tocopherol should not be given as a dietary supplement and should only be obtained from dietary sources to meet the body’s requirements due to the way it is stored, metabolized, and its strong interrelationships with other vitamin E isomers. On the other hand, vitamin E isomers in the form of tocotrienols and delta and gamma tocopherols have shown promising cancer-protective properties.
By Michael Jurgelewicz, DC, DACBN, DCBCN, CNS