Thursday, March 22, 2007

Two-timing Antioxidants

There are times when antioxidants are good. There are times when antioxidants aren't so good, for example, when they quench too many of the free radicals that our bodies use as signaling molecules.

The Case of Selenium and Insulin Resistance

In 2004, McClung et al., conducted a study on mice. Those with above average amounts of a selenium-containing enzyme (glutathione peroxidase: GP), which acts as an antioxidant, had higher rates of insulin resistance, a precursor to diabetes. They were also heavier and had more body fat than control mice. These changes occurred when certain free radicals which are used as signals in insulin function were rendered useless by too much of the antioxidant enzyme GP.

"Most people believe that both selenium and the selenium-containing enzyme GP are good for health by protecting cells and tissues from oxidation. However, this study suggests that they are a double-edged sword. Antioxidants can be harmful by neutralizing too many free radicals and interfering with insulin signaling, which results in promoting obesity, insulin resistance and possibly diabetes."
- Xingen Lei, study author

If you're interested, here's their study (free full access to boot):
Development Of Insulin Resistance And Obesity In Mice Overexpressing Cellular Glutathione Peroxidase

Sidenote: The current RDA for selenium is 55 micrograms/day (55 mcg/d) for men and women. The Tolerable Upper Intake Level (UL) is 400 mcg/d (400 mcg = 0.4 mg). Intakes above the UL may cause adverse effects. (See last paragraph.)

This is one more reason I'm reluctant to champion high-dose antioxidant supplements. However, antioxidants from food are a different story:
  1. You get a knock-down array of compounds. Where a pill may contain one carotenoid, e.g. beta-carotene, food contains hundreds of carotenoids - some found to work better when others were present (synergistic effect).
  2. If you're eating a variety of foods (and a sane number of calories), it's pretty difficult to consume too much of any one nutrient.
  3. A plateful of food tastes better that a plateful of pills. Forks better too.

Let me close with the story of a woman who experienced supplement-regret:
"Perhaps the most famous example of selenium toxicity was reported in 1984. About 11 days after starting to take supplemental selenium, a 57-year-old female who was otherwise in good health noted marked hair loss which progressed over a two-month period to almost total alopecia. She also noted white horizontal streaking on one fingernail, as well as tenderness and swelling on the fingertips and purulent discharge from the fingernail beds. All of her fingernails eventually became involved and she lost the entire fingernail of the first digit affected. She also experienced episodes of nausea, vomiting, a sour-milk breath odor, and increase in fatigue. She learned a little over three months later that the selenium tablets she had taken were recalled by the distributor because they, in error, contained over 27 milligrams of selenium per tablet, 182 times higher than labeled."
- PDRhealth - Selenium
Photo: Homegrown

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