Nutrition Science and Everyday Application - beta v 0.1

476 ALICE CALLAHAN, PHD, HEATHER LEONARD, MED, RDN, AND TAMBERLY POWELL, MS, RDN
radicals themselves or by adding energy that provokes electrons to move between atoms.
Excessive exposure to environmental sources of free radicals can contribute to disease by
overwhelming the free radical detoxifying systems and those processes involved in repairing
oxidative damage.
Oxidative stress is associated with the development of chronic diseases, and eating a
diet rich in antioxidant-containing foods like fruits, vegetables, and whole grains seems
to protect against many of these same diseases. It was thus natural for researchers to
hypothesize that taking antioxidants in supplement form might also offer protection from
these diseases. However, several decades of research investigating this hypothesis have
revealed disappointing results. Not only have these studies shown that antioxidant
supplements generally aren’t beneficial, some have shown that they can cause health risks.
For example, high doses of beta-carotene increased the risk of lung cancer in smokers,
and high doses of vitamin E increased the risk of prostate cancer in men. Antioxidant
supplements may also interact with other medications, further emphasizing the importance
of talking with your doctor before taking supplements. 2
Researchers aren’t sure why some antioxidant supplements have turned out to be
dangerous. It may come back to the fact that free radicals play important roles in the
body, and adding high doses of antioxidant supplements overwhelms the normal balance
of free radicals and does more harm than good. It may also be that the benefits of eating
antioxidant-rich foods come not just from the antioxidants but from the entire package of
nutrients, like fiber and phytochemicals in the whole foods, a combination that simply can’t
be replicated in a pill. Regardless, you can obtain adequate levels of dietary antioxidants
simply by eating a healthy diet. 1,2
Let’s take a closer look at several of the most important dietary antioxidants: vitamin E,
vitamin C, and selenium.
VITAMIN E
When we talk about vitamin E, we’re actually referring to 8 chemically similar substances,
of which alpha-tocopherol appears to be the most potent antioxidant. Because vitamin E is
fat-soluble, its antioxidant capacity is especially important to lipids, including those in cell
membranes and lipoproteins. For example, free radicals can oxidize LDL cholesterol (stealing
an electron from it), and it is this damaged LDL that lodges in blood vessels and forms the
fatty plaques characteristic of atherosclerosis, increasing the risk of heart attack, stroke, and
other complications of cardiovascular disease.
After alpha-tocopherol interacts with a free radical it is no longer capable of acting as an
antioxidant unless it is enzymatically regenerated. Vitamin C helps to regenerate some of
the alpha-tocopherol, but the remainder is eliminated from the body. Therefore, to maintain
vitamin E levels, you ingest it as part of your diet.
In addition to its antioxidant functions, vitamin E, mainly as alpha-tocopherol, plays a role
in the immune system, regulation of gene expression, and cell signaling. It also enhances the
dilation of blood vessels and inhibits blood clot formation.