Selenium

Daily Value: 70 micrograms

Good Food Sources: Lobster, Brazil nuts, clams, crab, cooked oysters, whole grains

Selenium may play a pivotal role in whether some viruses live harmlessly in the body or turn into rampaging pathogens that kill.

Laboratory studies at the University of North Carolina at Chapel Hill first suggested that selenium is the switch that triggers a Jekyll-and-Hyde personality in viruses. Subsequent studies at the University of Georgia in Athens indicated that selenium depletion in a cell may be what throws a switch on HIV, the virus that causes AIDS, and launches that particular viral terrorist on a cellular rampage that wipes out its human host. The irony is that the virus intends no harm. It is simply looking for more selenium.

If subsequent studies prove that selenium depletion is the trigger that shifts the AIDS virus into overdrive, the answer to keeping even this lethal virus in check may be as simple as making sure the body has adequate levels of selenium, says Will Taylor, Ph.D., an AIDS researcher at the University of Georgia, who led the Georgia study. For the full story on selenium and AIDS, see page 311.

Although its effect on viruses is probably selenium's most dramatic achievement, the mineral has other important roles in the body as well. It activates substances that protect the eyes from cataracts and the heart from muscle damage. It binds with toxic substances such as arsenic, cadmium and mercury to make them less harmful. It boosts several infection-fighting elements of your immune system.

And last but not least, selenium protects cells against damage from free radicals, naturally occurring maverick molecules that damage your body's healthy molecules by stealing electrons to balance themselves. Vitamin E has this same protective effect. In fact, selenium and vitamin E work so well together against free radicals that they frequently substitute for one another. That's why a deficiency of one of these nutrients can frequently lead to a deficiency of the other.

While there are no clear symptoms of selenium deficiency, some research has suggested that an insufficient level of the mineral may play a role in the development of heart disease.

Using Selenium Safely

As far back as the thirteenth century, Marco Polo noted that certain forages on which his animals grazed in western China caused the animals' hooves to drop off.

In subsequent centuries, scientists found that the cause was a toxic level of selenium in the plants that animals ate and that high levels of selenium in the diet could affect humans as well as horses. The only difference seems to be that humans lose hair and nails as opposed to hooves. Other side effects of excessive selenium intake include a persistent garlic odor on your breath and skin, a metallic taste in your mouth, dizziness and nausea for no apparent reason.

Today we know that the Daily Value is 70 micrograms. Some experts suggest that you look for a selenium supplement labeled "l-selenomethionine" and avoid those marked "sodium selenite" because l-selenomethionine is less likely to cause side effects and won't react with vitamin C to block selenium absorption.

To fight the AIDS virus, therapeutic doses of 200 to 400 micrograms have been suggested. But scientists caution that selenium supplements in excess of 100 micrograms per day should be taken only under medical supervision.

There is some debate over whether we need to take selenium supplements. Acid rain and the use of fossil fuels may be depleting the amount of selenium in the food chain. A further reduction in selenium intake can be linked to the many processed foods we eat. For these reasons, some experts have argued that the optimum amount of selenium may be much higher than the Daily Value suggests. The Brazil nut seems to be the richest source of selenium available. It takes only one or two nuts to meet the Daily Value.

If you are counting on the foods you eat as your primary source of selenium, here's something for you to think about. Plants get their selenium contents directly from the soil in which they grow. Generally, the soil in those states east of the Mississippi and west of the Rockies has a low selenium content. Crops that are grown in these areas will also have low selenium contents. Livestock is also affected, because the animals graze on plants grown in the same soil as our crops. Compounding this problem are the ions produced when we burn fossil fuels such as coal and oil. These ions acidify the soil, which hinders selenium uptake and reduces the amount of selenium found in the crops even more.