New Zealand's soil has a lack of selenium, but we make up for it in the sea

by Jennifer Bowden / 15 August, 2018
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Many Kiwis are deficient in selenium, which plays an important role in inflammation, immunity and the production of thyroid hormones.

Rich is a relative term – one man’s feast is another man’s famine. Or, as in this case, one man’s selenium-rich chicken would clearly be a poor excuse for a selenium source in another country – such as the US.

Selenium, which plays an important role in inflammation, immunity and the production of thyroid hormones, is an essential nutrient for humans. The populations of many countries have no difficulty getting enough selenium because it is widespread in the food supply through its presence in plant- and animal-derived foods.

The mineral is found in two forms: inorganic and organic, both of them good dietary selenium sources. Soil contains inorganic forms that plants take up and convert to organic forms. The brazil-nut tree, for example, is highly effective at accumulating selenium in its nuts.

Humans and animals that feed on those plants in turn accumulate the organic selenium in their tissues. Skeletal muscle is the major storage site. So, if selenium is abundant in soil, the plants and animals farmed on that land will be rich in the mineral, which makes it easy for consumers of those foods to get all they need.

If soil-selenium levels are low, however, as in New Zealand, it is harder to scrape together enough of the mineral from the various plant- and animal-derived food sources to meet our needs. Too little selenium has been linked to an increased risk of mortality, poor immune function and cognitive decline.

As I have noted before, many Kiwis are deficient in selenium. The average adult male and female consume just 67.0mcg and 47.1mcg a day respectively, less than the recommended 70mcg and 60mcg. American adults consume about double those amounts, men 134mcg and women 93mcg.

How do they do it? Quite easily. If a consumer ate 100g of sirloin steak, 100g of lean beef mince, 100g of roasted chicken breast and an egg produced in the US, they would be getting 116mcg of selenium. If, however, they ate New Zealand versions of those foods, they’d get just 42mcg of the mineral.

In this country, we scratch around for every last bit of selenium we can get. And yes, it’s correct – from a global perspective, our chicken is not a “rich” source of selenium. But relatively speaking, compared with other popular protein sources such as beef mince, it offers 10 times as much of the element.

The big difference in the selenium content of chicken versus red meat here probably comes down to the animals’ diet. Whereas our cattle are largely grazed and given some supplemental feed, poultry are fed a specially formulated diet, says Kerry Mulqueen of the Poultry Industry Association.

Their feed has been developed to deliver appropriate amounts of essential minerals such as selenium and copper, he says. “Their diets are totally controlled, and selenium is added to ensure they have enough.”

So, yes, chicken and eggs are a useful source of selenium, although they pale in comparison with fish and other seafood.

This article was first published in the July 28, 2018 issue of the New Zealand Listener.

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