Posted 4/2/12 on The Doctor Weighs In
Vitamin E is a fat-soluble vitamin that has antioxidant properties. It is present in vegetable oils (safflower, sunflower, corn, soybean), nuts (almonds, peanuts, hazelnuts), sunflower seeds, and green leafy vegetables (spinach, broccoli). A balanced diet provides all the vitamin E you need, but most people take supplements of the vitamin, on the assumption that if a little is good, more is better. Is it really so? Let’s examine the evidence.
The health claims of vitamin E
Vitamin E has been claimed to protect against heart disease, certain cancers, dementia, skin aging and scar formation. None of these claims has the data to support it. It does has a role in red blood cell formation and in vitamin K synthesis, which is important in blood clotting. But the amount of the vitamin needed for these functions is found in a well-balanced diet. So what’s the basis for all the other claims?
The chemical name of vitamin E is tocopherol, and it is present in two forms (isomers): alpha-tocophrol and gamma-tocopherol. The supplements are usually made up of the alpha-tocopherol isomer, but both forms are antioxidants.
Many studies have shown that oxygen radicals are part of the inflammatory process and are injurious to tissues. Hence the conclusion that vitamin E, being an antioxidant, must be “good for you”. EXCEPT, that the antioxidant effect is not the only biological activity of the vitamin. In fact, several studies failed to show a biological effect of the vitamin, itschemical antioxidant activity notwithstanding.
Bones are metabolically very active organs: they are being constantly resorbed by cells calledosteoclasts and built up by cells called osteoblasts. The balance between the two is crucial: if the activity of osteoclasts (the Yin half of the famous twins) is not balanced by the osteoblasts (the Yang half), osteoporosis is the all too familiar result. Postmenopausal women lose the antiinflammatory protection of estrogen, causing an accelerated resorption of bone. Under normal circumstances the osteoblasts would spring into action and work overtime to right the imbalance. And it is the gamma-tocopherol that apparently prods the osteoblasts into action. In the Journal of Bone and mineral research Maryam Hamidi and her colleagues showed that women who took vitamin E, comprising alpha-tocopherol, suppressed their levels of gamma-tocopherol, with the result that the natural balance between bone formation and bone resorption was disrupted, leading to loss of bone tissue.
How does it work?
Fujita and his colleagues (Nature Medicine) showed in mice what is happening. Alpha tocopherol, the synthetic form of vitamin E supplements, stimulates the formation of osteoclasts from precurser cells, and suppresses gamma-tocopherol, thus tilting the balance toward bone reosorption.
In summary: the first study showed suppression of gamma-tocopherol by alpha-tocopherol, the form we take as a vitamin E supplement. The second study, albeit in mice, showed in great molecular detail how alpha tocopherol enables the formation of osteoclasts, the destroyers of bone tissue.
There are two lessons here. First, we assumed that vitamin E exerts its influence by virtue of being an antioxidant. It is now evident that it has other effects, like stimulation of osteoclasts, that have nothing to do with antioxidant activity. Second, based on skimpy evidence we rushed to conclusions that were later shown to be inaccurate at best. In biology and medicine, conclusions based on “it makes sense” are simply not good enough. Biology is infinitely more complex than our powers of reasoning. We need to be a bit more humble.
What’s to be done?
My first preference would be to recommend having a diet rich in vegatables and other good sources of vitamin E. If you feel that you absolutely need supplementation, using multivitamins; the recommended RDA is 15 mg (or 22.4 International Units) a day. And by all means avoid the mega-doses of vitamin E pills.