NUTRITION NEWS

Featured Nutrient: Selenium

good sources of selenium

Promising news for fighting cancer.

By Peter Jaret, for EatingWell

Selenium should be one nutrient we don’t have to worry about: most Americans get double the recommended daily dose through diet. Still, this hasn’t stopped scientists from asking, “Are we getting enough?” Ongoing trials are examining whether high doses of selenium may help to prevent cancer; compelling animal research hints that the mineral may diminish the toxic effects of mercury in seafood.

Nutrient Newcomer

It’s not surprising that we’re still discovering selenium’s functions; the trace mineral wasn’t declared an essential nutrient until 1957, after research linked low selenium status with heart disease in children in some parts of China and other areas of the world where soils contained only sparse amounts of the mineral. Since selenium is absorbed into plants from the soil, its content in food crops—and in the animals that feed on the flora—varies widely depending on where the crops are grown. Luckily, most U.S. soil is rich in selenium. In the 1970s, scientists discovered selenium’s role in the body’s antioxidant system: it neutralizes unstable oxygen molecules before they damage healthy tissues.

The Cancer Connection

Also in the 1970s, animal studies began to suggest that high doses of selenium might protect against cancer. In 1983, a team of American scientists set out to investigate whether selenium supplements might offer similar benefits for humans: the findings of the 13-year clinical trial revealed that consuming 200 micrograms of selenium a day reduced total cancer incidence significantly; the protective effects appeared to be particularly potent against cancers of the lung, prostate and colon. Studies on selenium and cancer continue: one large trial currently is testing its effects on the development of prostate cancer.

Mercury Rising

The health benefits of fish are well-established, but federal agencies advise pregnant women to avoid varieties (swordfish, king mackerel, shark) with high levels of mercury, which can harm an unborn child’s brain development. Promising, then, is the recent report out of McGill University in Montreal that showed that supplementing rats with a combination of vitamin E and selenium protected the animals’ nervous and reproductive systems from mercury’s toxic effects. If confirmed, the preliminary findings could have substantial public health impact: last year, scientists at Mount Sinai School of Medicine in New York City revealed that, annually, as many as 637,233 infants born in the United States register mercury levels high enough to affect I.Q.

How much is enough?

For adults, the recommended daily allowance for selenium is 55 micrograms. While most Americans exceed this intake, it’s important to understand that RDAs are set based on the published scientific literature and, as new findings suggest additional benefits that may be gained with higher intakes, they could change. We’re not there yet: currently, experts don’t have enough data to say whether extra selenium actually does protect against cancer or mercury toxicity.

Until research reveals more, supplements aren’t recommended: too much selenium can cause stomach upset, fatigue and mild nerve damage. (The upper tolerable limit of supplemental selenium for adults is 400 micrograms a day.) Those looking to reap the promising but yet-unproven boons of the mineral can boost intake by including selenium-rich foods, such as shrimp, tuna, chicken, pork, whole-grain breads and cereals, in their diets. Brazil nuts are bursting with selenium—one ounce supplies ten times the RDA.

Selenium Selections
The following foods are considered good sources:	(MCG)
Brazil nuts (1 oz.)	543
Tuna, light, canned (3 oz.)	68
Pork (3 oz.)	40
Shrimp (3 oz.)	34
Oatmeal (1 cup)	19
Wheat bread (1 slice)	10
Source: ESHA database (2006)