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LINUS PAULING WAS WRONG about megavitamins because he had made two fundamental errors. First, he had assumed that you cannot have too much of a good thing. Vitamins are critical to life. If people don’t get enough vitamins, they suffer various deficiency states, like scurvy (not enough vitamin C) or rickets (not enough vitamin D). The reason that vitamins are so important is that they help convert food into energy. But there’s a catch. To convert food into energy, the body uses a process called oxidation. One outcome of oxidation is the generation of something called free radicals, which can be quite destructive. In search of electrons, free radicals damage cell membranes, DNA, and arteries, including the arteries that supply blood to the heart. As a consequence, free radicals cause cancer, aging, and heart disease. Indeed, free radicals are probably the single greatest reason that we aren’t immortal. To counter the effects of free radicals, the body makes antioxidants. Vitamins—like vitamins A, C, E, and beta-carotene—as well as minerals like selenium and substances like omega-3 fatty acids all have antioxidant activity. For this reason, people who eat diets rich in fruits and vegetables, which are rich in antioxidants, tend to have less cancer, less heart disease, and live longer. Pauling’s logic to this point is clear; if antioxidants in food prevent cancer and heart disease, then eating large quantities of manufactured antioxidants should do the same thing. But Linus Pauling had ignored one important fact: Oxidation is also required to kill new cancer cells and clear clogged arteries. By asking people to ingest large quantities of vitamins and supplements, Pauling had shifted the oxidation-antioxidation balance too far in favor of antioxidation, therefore inadvertently increasing the risk of cancer and heart disease. As it turns out, Mae West aside, you actually can have too much of a good thing. (“Too much of a good thing can be wonderful,” said West, who was talking about sex, not vitamins.) Second, Pauling had assumed that vitamins and supplements ingested in food were the same as those purified or synthesized in a laboratory. This, too, was incorrect. Vitamins are phytochemicals, which means that they are contained in plants (phyto- means “plant” in Greek). The 13 vitamins (A, B1, B2, B3, B5, B6, B7, B9, B12, C, D, E, and K) contained in food are surrounded by thousands of other phytochemicals that have long and complicated names like flavonoids, flavonols, flavanones, isoflavones, anthocyanins, anthocyanidins, proanthocyanidins, tannins, isothiocyanates, carotenoids, allyl sulfides, polyphenols, and phenolic acids. The difference between vitamins and these other phytochemicals is that deficiency states like scurvy have been defined for vitamins but not for the others. But make no mistake: These other phytochemicals are important, too. And Pauling’s recommendation to ingest massive quantities of vitamins apart from their natural surroundings was an unnatural act. For example, as described in Catherine Price’s book, Vitamania, half of an apple has the antioxidant activity of 1,500 milligrams of vitamin C, even though it contains only 5.7 milligrams of the vitamin. That’s because the phytochemicals that surround vitamin C in apples enhance its effect
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Paul A. Offit (Pandora's Lab: Seven Stories of Science Gone Wrong)